burton's microbiology for the health sciences 9th ed

BurtonsMICROBIOLOGY FOR THEHEALTH SCIENCES

Paul G. Engelkirk, PhD, MT(ASCP), SM(AAM)Biomedical Educational Services (Biomed Ed)Belton, TexasAdjunct Faculty, Biology DepartmentTemple College, Temple, TX

Janet Duben-Engelkirk, EdD, MT(ASCP)Biomedical Educational Services (Biomed Ed)Belton, TexasAdjunct Faculty, Biotechnology DepartmentTemple College, Temple, TX

N I N T H E D I T I O N

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Acquisitions Editor: David B. TroyProduct Manager: John LarkinManaging Editor: Laura S. Horowitz, Hearthside Publishing ServicesMarketing Manager: Allison PowellDesigner: Steve DrudingCompositor: Maryland Composition/Absolute Service Inc.

Ninth Edition

Copyright 2011 Lippincott Williams & Wilkins, a Wolters Kluwer business 2007 Lippincott Williams & Wilkins, 2004 Lippincott Williams & Wilkins, 2000Lippincott Williams & Wilkins, 1996 Lippincott-Raven, 1992, 1988, 1983, 1979 JB Lippincott Co.

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Library of Congress Cataloging-in-Publication Data

Engelkirk, Paul G.Burtons microbiology for the health sciences / Paul G. Engelkirk, Janet Duben-Engelkirk. 9th ed.

p. ; cm.Includes bibliographical references and index.ISBN 978-1-60913-321-4

1. Microbiology. 2. Medical microbiology. 3. Allied health personnel. I. Burton, Gwendolyn R. W.(Gwendolyn R. Wilson) II. Duben-Engelkirk, Janet L. III. Title. IV. Title: Microbiology for the health sciences.

[DNLM: 1. Microbiological Processes. 2. Communicable Diseasesmicrobiology. QW 4 E575b 2011]QR41.2.B88 2010616.9'041dc22

2009036495

DISCLAIMER

Care has been taken to confirm the accuracy of the information present and to describe generally acceptedpractices. However, the authors, editors, and publisher are not responsible for errors or omissions or for anyconsequences from application of the information in this book and make no warranty, expressed or implied,with respect to the currency, completeness, or accuracy of the contents of the publication. Application of thisinformation in a particular situation remains the professional responsibility of the practitioner; the clinical treat-ments described and recommended may not be considered absolute and universal recommendations.

The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage setforth in this text are in accordance with the current recommendations and practice at the time of publication.However, in view of ongoing research, changes in government regulations, and the constant flow of informationrelating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug forany change in indications and dosage and for added warnings and precautions. This is particularly importantwhen the recommended agent is a new or infrequently employed drug.

Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA)clearance for limited use in restricted research settings. It is the responsibility of the healthcare provider toascertain the FDA status of each drug or device planned for use in their clinical practice.

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Dedicated to the original author of this book,Dr. Gwendolyn R.W. Burton,

whose spirit lives on within its pages.

Gwen,we will remember you,

think of you,pray for you.

And when another day is through,well still be friends with you.

(paraphrased lyrics of a song by the late and much loved John Denver)

AND

To our parents,without whose love and support,

we could have neverfulfilled our dreams.

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Paul G. Engelkirk, PhD, MT(ASCP), SM(AAM), is a retiredprofessor of biological sciences in the Science Departmentat Central Texas College in Killeen, Texas, where hetaught introductory microbiology for 12 years. Beforejoining Central Texas College, he was an associate profes-sor at the University of Texas Health Science Center inHouston, Texas, where he taught diagnostic microbiol-ogy to medical technology students for 8 years. Prior tohis teaching career, Dr. Engelkirk served 22 years as anofficer in the U.S. Army Medical Department, supervis-ing various immunology, clinical pathology, and microbi-ology laboratories in Germany, Vietnam, and the UnitedStates. He retired from the Army with the rank ofLieutenant Colonel.

Dr. Engelkirk received his bachelors degree in biol-ogy from New York University and his masters and doc-torate degree (both in microbiology and public health)from Michigan State University. He received additionalmedical technology and tropical medicine training atWalter Reed Army Hospital in Washington, D.C., andspecialized training in anaerobic bacteriology, myco-bacteriology, and virology at the Centers for DiseaseControl and Prevention in Atlanta, Georgia.

Dr. Engelkirk is the author or coauthor of four mi-crobiology textbooks, 10 additional book chapters, fivemedical laboratory-oriented self-study courses, and manyscientific articles. He also served for 14 years as coeditorof four separate newsletters for clinical microbiology lab-oratory personnel. Dr. Engelkirk has been engaged invarious aspects of clinical microbiology for more than45 years and is a past president of the Rocky MountainBranch of the American Society for Microbiology. Heand his wife, Janet, currently provide biomedical educa-tional services through their consulting business (BiomedEd), located in Belton, Texas. Dr. Engelkirks hobbies in-clude RVing, hiking, kayaking, nature photography, writ-ing, and working in his yard.

Janet Duben-Engelkirk, EdD, MT(ASCP), has over 30 yearsof experience in clinical laboratory science and higher ed-ucation. She received her bachelors degrees in biology andmedical technology and her masters degree in technicaleducation from the University of Akron, and her doctoratein allied health education and administration from a com-bined program through the University of Houston andBaylor College of Medicine in Houston, Texas.

Dr. Duben-Engelkirk began her career in clinicallaboratory science education teaching students on thebench in a community hospital in Akron, Ohio. Shethen became Education Coordinator for the ClinicalLaboratory Science Program at the University of TexasHealth Science Center at Houston, where she taught

clinical chemistry and related subjects for 12 years. In1992, Dr. Duben-Engelkirk assumed the position ofDirector of Allied Health and Clinical LaboratoryScience Education at Scott and White Hospital inTemple, Texas, wherein her responsibilities includedteaching microbiology and clinical chemistry. She alsoserved as Interim Program Director for the MedicalLaboratory Technician program at Temple College. In2006, Dr. Duben-Engelkirk assumed the position ofchair of the biotechnology department at the TexasBioscience Institute and Temple College, where she wasresponsible for curriculum development and administra-tion of the biotechnology degree programs. She is nowsemiretired and teaching online biotechnology coursesfor the Temple College Biotechnology Department. Sheand her husband, Paul, are also co-owners of a biomed-ical education consulting business.

Dr. Duben-Engelkirk was coeditor of a widely usedclinical chemistry textbook and coauthored a clinicalanaerobic bacteriology textbook with Paul. She has au-thored or coauthored numerous book chapters, journalarticles, self-study courses, newsletters, and other educa-tional materials over the course of her career.

Dr. Duben-Engelkirk has received many awards dur-ing her career, including Outstanding Young Leader inAllied Health, the American Society for ClinicalLaboratory Sciences Omicron Sigma Award for out-standing service, and Teaching Excellence Awards. Herprofessional interests include instructional technology,computer-based instruction, and distance education.Outside of the office and classroom, Dr. Duben-Engelkirk enjoys taking cruises, reading, music, yoga,movies, hiking, and camping.

ABOUT THE AUTHORS

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PREFACE

Microbiologythe study of microbesis a fascinatingsubject that impacts our daily lives in numerous ways.Microbes live on us and in us. They are vital in manyindustries. Microbes are essential for the cycling andrecycling of elements such as carbon, oxygen, and nitro-gen, and provide most of the oxygen in our atmosphere.They are used to clean up toxic wastes. Microbes areused in genetic engineering and gene therapy. And, ofcourse, many microbes cause disease. In recent years,the public has been bombarded with news reports aboutmicrobe-associated medical problems such as swine flu,bird flu, severe acute respiratory syndrome (SARS),flesh-eating bacteria, mad cow disease, superbugs, blackmould in buildings, West Nile virus, bioterrorism, an-thrax, smallpox, food recalls as a result of Escherichia coliand Salmonella contamination, and epidemics ofmeningitis, hepatitis, influenza, tuberculosis, and diar-rheal diseases.

WRITTEN FOR HEALTHCAREPROFESSIONALS

Burtons Microbiology for the Health Sciences has been writ-ten primarily for nurses and other healthcare profession-als. This book provides students of these professions withvital microbiology information that will enable them tocarry out their duties in an informed, safe, and efficientmanner. It is appropriate for use in any one-semester in-troductory microbiology course, whether for students ofthe healthcare professions or for science or biology ma-jors. Unlike many of the other introductory microbiol-ogy texts on the market, all of the material in this bookcan be covered in a single semester.

Chapters of special importance to students of thehealthcare professions include those dealing with antibi-otics and other antimicrobial agents, epidemiology andpublic health, healthcare-associated infections, infectioncontrol, how microbes cause disease, how our bodiesprotect us from pathogens and infectious diseases, andthe major viral, bacterial, fungal, and parasitic diseasesof humans.

NEW TO THE NINTH EDITION

The most obvious changes in the ninth edition are an in-creased number of color illustrations and the redistribu-tion of information about infectious diseases. The eightheditions lengthy and somewhat cumbersome chapter oninfectious diseases (Chapter 17) has been divided intofive chapters (Chapters 17 through 21 in the ninth edi-tion). The artwork has been expanded and updated to

make it more useful and more appealing. Color illustra-tions appear throughout the book, rather than beinggrouped together in one location. The book is dividedinto eight major sections, containing a total of 21 chap-ters. Each chapter contains a Chapter Outline, LearningObjectives, Self-Assessment Exercises, and informationabout the contents of the Student CD-ROM. Interestinghistorical information, in the form of Historical Notes,is spread throughout the book and is presented in appro-priate chapters.

STUDENT-FRIENDLY FEATURES

The authors have made every attempt to create a stu-dent-friendly book. The book can be used by all types ofstudents, including those with little or no science back-ground and mature students returning to school after anabsence of several years. It is written in a clear and con-cise manner. It contains more than 30 Study Aid boxes,which summarize important information and explain dif-ficult concepts and similar-sounding terms. New termsare highlighted and defined in the text, and are includedin a Glossary at the back of the book.

Answers to Self-Assessment Exercises contained inthe book can be found in Appendix A. Appendix B con-tains a summary of key points about the most importantbacterial pathogens discussed in the book. In the past,students have found this appendix to be especially help-ful. Appendix C contains useful formulas for conversionof one type of unit to another (e.g., Fahrenheit to Celsiusand vice versa). Because Greek letters are commonly usedin microbiology, the Greek alphabet can be found inAppendix D.

STUDENT CD-ROM

The Student CD-ROM included with the book providesa vast amount of supplemental information.

Each section of the CD-ROM includes the primaryobjectives of the chapter, a list of new terms introducedin the chapter, a review of key points, and sections enti-tled Insight, Increase Your Knowledge, and CriticalThinking. Case Studies are provided for the chapters oninfectious diseases. The Student CD-ROM also containsanswers to the Self-Assessment Exercises found in thebook, and additional Self-Assessment Exercises with an-swers. Instructor information on thePoint includessuggested laboratory exercises, suggested audiovisualaids, an image bank, a test generator, and answers to thevarious Case Studies and Self-Assessment Exercises inthe book and on the Student CD-ROM.

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vi Preface

TO OUR READERS

As you will discover, the concise nature of this book makeseach sentence significant. Thus, you will be intellectuallychallenged to learn each new concept as it is presented. Itis our hope that you will enjoy your study of microbiologyand be motivated to further explore this exciting field, es-pecially as it relates to your occupation. Many studentswho have used this textbook in their introductory micro-biology course have gone on to become infection controlnurses, epidemiologists, clinical laboratory scientists (med-ical technologists), and microbiologists.

OUR THANKS

We are deeply indebted to all of the people who helpedwith the editing and publication of this book. Special

thanks to our extremely efficient Managing Editor,Ms. Laura Horowitz, who was an absolute delight towork with; to Gregory Bond, MSN, for his thoroughreview of the previous edition; to the authors of otherLippincott Williams & Wilkins textbooks, whose illus-trations appear throughout the book; to Dr. PatrickHidy, RN, and Christine Vernon, for providing many ofthe drawings; and to David B. Troy, Acquisitions Editor;Allison Powell, Marketing Manager; and MeredithBrittain and John Larkin, Product Managers fromLippincott Williams & Wilkins.

Paul G. Engelkirk, PhD, MT(ASCP), SM(AAM)Janet Duben-Engelkirk, EdD, MT(ASCP)

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In todays health careers, a thorough understanding ofmicrobiology is more important than ever. BurtonsMicrobiology for the Health Sciences, Ninth Edition, not onlyprovides the conceptual knowledge you will need but alsoteaches you how to apply it. This Users Guide intro-duces you to the features and tools of this innovative text-book. Each feature is specifically designed to enhanceyour learning experience, preparing you for a successfulcareer as a health professional.

CHAPTER OPENER FEATURES

The features that open each chapter are an introductionto guide you through the remainder of the lesson.

Chapter OutlineServes as a roadmap to the material ahead.

Learning ObjectivesHighlight important conceptshelping you to organizeand prioritize learning.

IntroductionFamiliarizes you with the material covered in the chapter.

CHAPTER FEATURES

The following features appear throughout the body ofthe chapter. They are designed to hone critical thinkingskills and judgment, build clinical proficiency, and pro-mote comprehension and retention of the material.

Historical Note BoxesProvide insight into the history and development

of microbiology and healthcare.

Spotlighting BoxesA new feature spotlighting healthcare careers.

Study Aid BoxesSummarize key information, explain difficult con-

cepts, and differentiate similar-sounding terms.

Clinical Procedure BoxesSet forth step-by-step instructions for common

procedures.

USERS GUIDE

Something To Think AboutThese boxes contain information that will stimu-

late students to ponder interesting possibilities.

Test Preparation FeaturesThese features help you review chapter content and testyourself before exams.

Highlighted Key PointsHelp you pinpoint the main ideas of the text.

Self-Assessment ExercisesHelp you gauge your understanding of what you havelearned.

On the CD-ROM Box Directs you to additional content and exercises for

review on the companion CD-ROM.

BONUS CD-ROM

Packaged with this textbook, the CD-ROM is a powerfullearning tool. It includes the following features that helpreinforce and review the material covered in the book:

Chapter Learning Tools Primary Objectives of Each Chapter Lists of New Terms Introduced in Each Chapter Review of Key Points Answers to Text-Based Exercises Additional Self-Assessment Exercises with Answers

Also included are special Insight, Increase YourKnowledge, Critical Thinking, and Case Study sec-tions that provide additional information and exercises aswell as fun facts on selected topics from the text.

Additional Appendices1. Microbial Intoxications2. Phyla and Medically Significant Genera within the

Domain Bacteria3. Basic Chemistry Concepts4. Responsibilities of the Clinical Microbiology

Laboratory5. Clinical Microbiology Laboratory Procedures6. Preparing Solutions and Dilutions

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Preface v

S E C T I O N I

Introduction to Microbiology

C h a p t e r 1MicrobiologyThe Science . . . . . . . . . . . . . . . 1Introduction 1What is Microbiology? 1Why Study Microbiology? 2First Microorganisms on Earth 6Earliest Known Infectious Diseases 6Pioneers in the Science of Microbiology 6Careers in Microbiology 11

C h a p t e r 2Viewing the Microbial World . . . . . . . . . . . . . 13Introduction 13Using the Metric System to Express the Sizes of

Microbes 13Microscopes 14

S E C T I O N I I

Introduction to Microbes and Cellular Biology

C h a p t e r 3Cell Structure and Taxonomy . . . . . . . . . . . . . 24Introduction 24Eucaryotic Cell Structure 25Procaryotic Cell Structure 28Summary of Structural Differences Between Procaryotic and

Eucaryotic Cells 34Reproduction of Organisms and Their Cells 35Taxonomy 35Determining Relatedness Among Organisms 38

C h a p t e r 4Microbial Diversity . . . . . . . . . . . . . . . . . . . . 40Part 1 Acellular and Procaryotic Microbes 40Introduction 40Acellular Microbes 41The Domain Bacteria 52The Domain Archaea 66

C h a p t e r 5Microbial Diversity . . . . . . . . . . . . . . . . . . . . 69Part 2 Eucaryotic Microbes 69Introduction 69Algae 69Protozoa 72Fungi 74Lichens 82Slime Moulds 82

S E C T I O N I I I

Chemical and Genetic Aspects ofMicroorganismsC h a p t e r 6Biochemistry: The Chemistry of Life . . . . . . . . 84Introduction 84Organic Chemistry 85Biochemistry 86

C h a p t e r 7Microbial Physiology and Genetics . . . . . . . . 102Microbial Physiology 102Metabolic Enzymes 104Metabolism 106Bacterial Genetics 111Genetic Engineering 118Gene Therapy 118

S E C T I O N I V

Controlling the Growth of MicrobesC h a p t e r 8Controlling Microbial Growth In Vitro . . . . . . 121Introduction 122Factors that Affect Microbial Growth 122Encouraging the Growth of Microbes In Vitro 124Inhibiting the Growth of Microbes In Vitro 131

C h a p t e r 9Controlling Microbial Growth In Vivo UsingAntimicrobial Agents . . . . . . . . . . . . . . . . . 140Introduction 140Characteristics of an Ideal Antimicrobial Agent 142How Antimicrobial Agents Work 142Antibacterial Agents 142Antifungal Agents 148Antiprotozoal Agents 148Antiviral Agents 148Drug Resistance 149Some Stategies in the War Against Drug Resistance 154Empiric Therapy 154Undesirable Effects of Antimicrobial Agents 156Concluding Remarks 156

S E C T I O N V

Environmental and Applied MicrobiologyC h a p t e r 1 0Microbial Ecology and Microbial Biotechnology . . . . . . . . . . . . . . . . . . . . . . 158Introduction 158Symbiotic Relationships Involving Microorganisms 159

viii

CONTENTS

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Contents ix

Indigenous Microflora of Humans 160Beneficial and Harmful Roles of Indigenous Microflora 164Microbial Communities (Biofilms) 165Agricultural Microbiology 166Microbial Biotechnology 168

C h a p t e r 1 1Epidemiology and Public Health . . . . . . . . . . 171Epidemiology 171Interactions Among Pathogens, Hosts, and

Environments 177Chain of Infection 178Strategies for Breaking the Chain of Infection 179Reservoirs of Infection 179Modes of Transmission 183Public Health Agencies 186Bioterrorism and Biological Warfare Agents 188Water Supplies and Sewage Disposal 192

S E C T I O N V I

Microbiology within Healthcare Facilities

C h a p t e r 1 2Healthcare Epidemiology . . . . . . . . . . . . . . . 196Introduction 196Healthcare-Associated Infections 197Infection Control 201Concluding Remarks 219

C h a p t e r 1 3Diagnosing Infectious Diseases . . . . . . . . . . 220Introduction 220Clinical Specimens 220The Pathology Department (The Lab) 229The Clinical Microbiology Laboratory 231

S E C T I O N V I I

Pathogenesis and Host Defense Mechanisms

C h a p t e r 1 4Pathogenesis of Infectious Diseases . . . . . . . 238Introduction 238Infection versus Infectious Disease 239Why Infection Does Not Always Occur 239Four Periods or Phases in the Course of an

Infectious Disease 239Localized versus Systemic Infections 240Acute, Subacute, and Chronic Diseases 240Symptoms of a Disease versus Signs of a Disease 240Latent Infections 241Primary versus Secondary Infections 241Steps in the Pathogenesis of Infectious Diseases 242Virulence 242Virulence Factors 243

C h a p t e r 1 5Nonspecific Host Defense Mechanisms . . . . . . 251Introduction 251Nonspecific Host Defense Mechanisms 252

First Line of Defense 253Second Line of Defense 254

C h a p t e r 1 6Specific Host Defense Mechanisms: An Introduction to Immunology . . . . . . . . . . 266Introduction 266The Key to Understanding Immunology 267Primary Functions of the Immune System 267Major Arms of the Immune System 267Immunity 268Cells of the Immune System 272Where Do Immune Responses Occur? 273Humoral Immunity 273Cell-Mediated Immunity 279Hypersensitivity and Hypersensitivity Reactions 280Autoimmune Diseases 285Immunosuppression 285The Immunology Laboratory 286

S E C T I O N V I I I

Major Infectious Diseases of Humans

C h a p t e r 1 7Overview of Infectious Diseases . . . . . . . . . . 291Introduction 291Infectious Diseases of the Skin 292Infectious Diseases of the Ears 293Infectious Diseases of the Eyes 293Infectious Diseases of the Respiratory System 293Infectious Diseases of the Oral Region 296Infectious Diseases of the Gastrointestinal Tract 297Infectious Diseases of the Genitourinary System 297Infectious Diseases of the Circulatory System 301Infectious Diseases of the Central Nervous System 302Opportunistic Infections 305Emerging and Reemerging Infectious Diseases 305

C h a p t e r 1 8Viral Infections . . . . . . . . . . . . . . . . . . . . . 307Introduction 307How Do Viruses Cause Disease? 307Viral Infections of the Skin 308Viral Infections of the Ears 312Viral Infections of the Eyes 312Viral Infections of the Respiratory System 312Viral Infections of the Oral Region 313Viral Infections of the Gastrointestinal Tract 313Viral Infections of the Genitourinary System 316Viral Infections of the Circulatory System 316Viral Infections of the Central Nervous System 320Recap of Major Viral Infections of Humans 320Appropriate Therapy for Viral Infections 320

C h a p t e r 1 9Bacterial Infections . . . . . . . . . . . . . . . . . . 323Introduction 323How Do Bacteria Cause Disease? 325Bacterial Infections of the Skin 325Bacterial Infections of the Ears 327

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x Contents

Bacterial Infections of the Eyes 329Bacterial Infections of the Respiratory System 329Bacterial Infections of the Oral Region 332Bacterial Infections of the Gastrointestinal Tract 334Bacterial Infections of the Genitourinary System 337Bacterial Infections of the Circulatory System 340Bacterial Infections of the Central Nervous System 344Diseases Caused by Anaerobic Bacteria 344Diseases Associated with Biofilms 344Recap of Major Bacterial Infections of Humans 345Appropriate Therapy for Bacterial Infections 347

C h a p t e r 2 0Fungal Infections . . . . . . . . . . . . . . . . . . . . 348Introduction 348How Do Fungi Cause Disease? 348Classification of Fungal Diseases 349Fungal Infections of the Skin 351Fungal Infections of the Respiratory System 351Fungal Infections of the Oral Region 351Fungal Infections of the Genitourinary System 353Fungal Infections of the Circulatory System 354Fungal Infections of the Central Nervous System 354Recap of Major Fungal Infections of Humans 355Appropriate Therapy for Fungal Infections 355

C h a p t e r 2 1Parasitic Infections . . . . . . . . . . . . . . . . . . 357Introduction 357Definitions 358

How Parasites Cause Disease 359Parasitic Protozoa 359Protozoal Infections of Humans 359Helminths 367Helminth Infections of Humans 369Appropriate Therapy for Parasitic Infections 369Medically Important Arthropods 370

A P P E N D I C E S

A p p e n d i x AAnswers to Self-Assessment Exercises . . . . . . 373

A p p e n d i x BCompendium of Important Bacterial Pathogens of Humans . . . . . . . . . . . . . . . . . 375

A p p e n d i x CUseful Conversions . . . . . . . . . . . . . . . . . . . 378

A p p e n d i x DGreek Alphabet . . . . . . . . . . . . . . . . . . . . . 379

Glossary 381Index 405

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LEARNING OBJECTIVES

AFTER STUDYING THIS CHAPTER, YOU SHOULD BE ABLE TO:

Define microbiology, pathogen, nonpathogen, and op-portunistic pathogen

Differentiate between acellular microbes and microor-ganisms and list several examples of each

List several reasons why microbes are important (e.g., asa source of antibiotics)

Explain the relationship between microbes and infec-tious diseases

Differentiate between infectious diseases and microbialintoxications

Outline some of the contributions of Leeuwenhoek,Pasteur, and Koch to microbiology

Differentiate between biogenesis and abiogenesis Explain the germ theory of disease Outline Kochs Postulates and cite some circumstances in

which they may not apply Discuss two medically related fields of microbiology

INTRODUCTION

Welcome to the fascinating world of microbiology,where you will learn about creatures so small that theycannot be seen with the naked eye. In this chapter, youwill discover the effects that these tiny creatures have onour daily lives and the environment around us, and whyknowledge of them is of great importance to healthcareprofessionals. You will learn that some of them are ourfriends, whereas others are our enemies. You are about toembark on an exciting journey. Enjoy the adventure!

WHAT IS MICROBIOLOGY?

The study of microbiology isessentially an advanced biol-ogy course. Ideally, studentstaking microbiology will havesome background in biology.Although biology is the study ofliving organisms (from bios, re-ferring to living organisms, and logy, meaning the studyof), microbiology includes the study of certain nonlivingentities as well as certain living organisms. Collectively,these nonliving entities and living organisms are called mi-crobes. Micro means very smallanything so small that itmust be viewed with a microscope (an optical instrumentused to observe very small objects). Therefore, microbiol-ogy can be defined as the study of microbes. Individual mi-crobes can be observed only with the use of various types ofmicroscopes. Microbes are said to be ubiquitous, meaningthey are virtually everywhere.

The various categories ofmicrobes include viruses, bacte-ria, archaea, protozoa, and cer-tain types of algae and fungi(Fig. 1-1). These categories ofmicrobes are discussed in detailin Chapters 4 and 5. Becausemost scientists do not considerviruses to be living organisms,they are often referred to asacellular microbes or infec-tious particles rather thanmicroorganisms.

1

S E C T I O N I

Introduction to Microbiology

MICROBIOLOGYTHE SCIENCE 1CHAPTER OUTLINE

INTRODUCTIONWHAT IS MICROBIOLOGY?WHY STUDY MICROBIOLOGY?FIRST MICROORGANISMS ON EARTH

EARLIEST KNOWN INFECTIOUSDISEASES

PIONEERS IN THE SCIENCEOF MICROBIOLOGY

Anton van LeeuwenhoekLouis Pasteur

Robert KochKochs PostulatesExceptions to Kochs Postulates

CAREERS IN MICROBIOLOGYMedical and Clinical Microbiology

Microbiology is thestudy of microbes.Individual microbescan be observed onlywith the use of varioustypes of microscopes.

The two majorcategories of microbesare called acellularmicrobes (also calledinfectious particles) andcellular microbes (alsocalled microorganisms).Acellular microbesinclude viruses andprions. Cellular microbesinclude all bacteria, allarchaea, some algae, allprotozoa, and somefungi.

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Your first introduction tomicrobes may have been whenyour mother warned you aboutgerms (Fig. 1-2). Althoughnot a scientific term, germs arethe microbes that cause disease.Your mother worried that you might become infectedwith these types of microbes. Disease-causing microor-ganisms are technically known as pathogens (also re-ferred to as infectious agents) (Table 1-1). Actually, onlyabout 3% of known microbes are capable of causingdisease (i.e., only about 3% are pathogenic). Thus, thevast majority of known microbes are nonpathogensmicrobes that do not cause disease. Some nonpathogensare beneficial to us, whereas others have no effect on us atall. In newspapers and on television, we read and hearmore about pathogens than we do about nonpathogens,but in this book you will learn about both categoriesthemicrobes that help us (microbial allies) and those thatharm us (microbial enemies).

WHY STUDY MICROBIOLOGY?

Although they are very small, microbes play significantroles in our lives. Listed below are a few of the many rea-sons to take a microbiology course and to learn aboutmicrobes:

We have, living on and inour bodies (e.g., on our skinand in our mouths and intes-tinal tract), approximately10 times as many microbes

as the total number of cells (i.e., epithelial cells, nervecells, muscle cells, etc.) that make up our bodies (10trillion cells 10 100 trillion microbes). It hasbeen estimated that perhaps as many as 500 to 1,000different species of microbes live on and in us.Collectively, these microbes are known as our indige-nous microflora (or indigenous microbiota) and, forthe most part, they are of benefit to us. For example,the indigenous microflora inhibit the growth ofpathogens in those areas of the body where they liveby occupying space, depleting the food supply, andsecreting materials (waste products, toxins, antibi-otics, etc.) that may prevent or reduce the growth ofpathogens. Indigenous microflora are discussed morefully in Chapter 10.

Some of the microbes thatcolonize (inhabit) our bodiesare known as opportunisticpathogens (or opportunists).Although these microbesusually do not cause us anyproblems, they have the po-tential to cause infections ifthey gain access to a part ofour anatomy where they do not belong. For example,

2 SECTION I Introduction to Microbiology

Microbes

Acellular Infectious AgentsPrionsViruses

CellularMicroorganisms

ProcaryotesArchaeaBacteria

EucaryotesAlgaeFungi

Protozoa

FIGURE 1-1. Acellular and cellular microbes.Acellular microbes (also known as infectious particles) include prions and viruses. Cellular microbes include theless complex procaryotes (organisms composed of cellsthat lack a true nucleus, such as archaea and bacteria)and the more complex eucaryotes (organisms composed ofcells that contain a true nucleus, such as algae, protozoa,and fungi). Procaryotes and eucaryotes are discussedmore fully in Chapter 3.

FIGURE 1-2. Germs. In all likelihood, your motherwas your first microbiology instructor. Not only did shealert you to the fact that there were invisible critters inthe world that could harm you, she also taught you thefundamentals of hygienelike handwashing.

Dont touch thatfilthy thing.Its coveredwith germs.

Microbes that causedisease are known aspathogens. Those thatdo not cause disease arecalled nonpathogens.

The microbes that liveon and in the humanbody are referred to asour indigenousmicroflora.

Opportunistic pathogensdo not cause diseaseunder ordinaryconditions, but havethe potential to causedisease should theopportunity presentitself.

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a bacterium called Escherichia coli (E. coli) lives in ourintestinal tracts. This organism does not cause us anyharm as long as it remains in our intestinal tract butcan cause disease if it gains access to our urinary blad-der, bloodstream, or a wound. Other opportunisticpathogens strike when a person becomes run-down,stressed-out, or debilitated (weakened) as a resultof some disease or condition. Thus, opportunisticpathogens can be thought of as microbes awaiting theopportunity to cause disease.

Microbes are essential for life on this planet as weknow it. For example, some microbes produce oxygenby the process known as photosynthesis (discussed inChapter 7). Actually, microbes contribute more oxygento our atmosphere than do plants. Thus, organisms

that require oxygenhumans, for exampleowe adebt of gratitude to the algae and cyanobacteria (agroup of photosynthetic bacteria) that produce oxygen.

Many microbes are involved in the decomposition ofdead organisms and the waste products of living or-ganisms. Collectively, they are referred to as decom-posers or saprophytes. By definition, a saprophyte isan organism that lives on dead or decaying organicmatter. Imagine living in a world with no decom-posers. Not a pleasant thought! Saprophytes aid infertilization by returning inorganic nutrients to thesoil. They break down dead and dying organic mate-rials (plants and animals) into nitrates, phosphates,and other chemicals necessary for the growth ofplants (Fig. 1-3).

CHAPTER 1 MicrobiologyThe Science 3

CATEGORY EXAMPLES OF DISEASES THEY CAUSE

Algae A very rare cause of infections; intoxications (which result from ingestion of toxins)

Bacteria Anthrax, botulism, cholera, diarrhea, diphtheria, ear and eye infections, food poisoning, gas gangrene, gonor-rhea, hemolytic uremic syndrome (HUS), intoxications, Legionnaires disease, leprosy, Lyme disease, meningi-tis, plague, pneumonia, Rocky Mountain spotted fever, scarlet fever, staph infections, strep throat, syphilis,tetanus, tuberculosis, tularemia, typhoid fever, typhus, urethritis, urinary tract infections, whooping cough

Fungi Allergies, cryptococcosis, histoplasmosis, intoxications, meningitis, pneumonia, thrush, tinea (ringworm)infections, yeast vaginitis

Protozoa African sleeping sickness, amebic dysentery, babesiosis, Chagas disease, cryptosporidiosis, diarrhea, giar-diasis, malaria, meningoencephalitis, pneumonia, toxoplasmosis, trichomoniasis

Viruses Acquired immunodeficiency syndrome (AIDS), bird flu, certain types of cancer, chickenpox, cold sores(fever blisters), common cold, dengue, diarrhea, encephalitis, genital herpes infections, German measles,hantavirus pulmonary syndrome (HPS), hemorrhagic fevers, hepatitis, infectious mononucleosis, influenza,measles, meningitis, monkeypox, mumps, pneumonia, polio, rabies, severe acute respiratory syndrome(SARS), shingles, smallpox, warts, yellow fever

PathogensTABLE 1-1

Saprophytes and

organic material

Soil Nitrates Phosphates Sulfates

Ammonia Carbon dioxide Water and other chemicals

FIGURE 1-3. Saprophytes. Saprophytes break down dead and decaying organic material intoinorganic nutrients in the soil.

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Some microbes are capable of decomposing industrialwastes (oil spills, for example). Thus, we can use mi-crobesgenetically engineered microbes, in somecasesto clean up after ourselves. The use of microbesin this manner is called bioremediation, a topic dis-cussed in more detail in Chapter 10. Genetic engi-neering is discussed briefly in a following section andmore fully in Chapter 7.

Many microbes are involved in elemental cycles, suchas the carbon, nitrogen, oxygen, sulfur, and phospho-rous cycles. In the nitrogen cycle, certain bacteria con-vert nitrogen gas in the air to ammonia in the soil.Other soil bacteria then convert the ammonia to ni-trites and nitrates. Still other bacteria convert the nitro-gen in nitrates to nitrogen gas, thus completing thecycle (Fig. 1-4). Knowledge of these microbes is impor-tant to farmers who practice crop rotation to replenishnutrients in their fields and to gardeners who keepcompost pits as a source of natural fertilizer. In bothcases, dead organic material is broken down into inor-ganic nutrients (e.g., nitrates and phosphates) by mi-crobes. The study of the relationships betweenmicrobes and the environment is called microbialecology. Microbial ecology and the nitrogen cycle arediscussed more fully in Chapter 10.

Algae and bacteria serve as food for tiny animals. Then,larger animals eat the smaller creatures, and so on.Thus, microbes serve as important links in food chains(Fig. 1-5). Microscopic organisms in the ocean, collec-tively referred to as plankton, serve as the starting

point of many food chains. Tiny marine plants andalgae are called phytoplankton, whereas tiny marineanimals are called zooplankton.

Some microbes live in the intestinal tracts of animals,where they aid in the digestion of food and, in somecases, produce substances that are of value to the hostanimal. For example, the E. coli bacteria that live in thehuman intestinal tract produce vitamins K and B1,which are absorbed and used by the human body.Although termites eat wood, they cannot digest wood.Fortunately for them, termites have cellulose-eatingprotozoa in their intestinal tracts that break down thewood that the termites consume into smaller moleculesthat the termites can use as nutrients.


Nitrogen gas in the air

Legumes

Nitrogen returns to air

Nitrogen- fixing bacteria

Nitrates to replenish the soil nutrients

FIGURE 1-4. Nitrogen fixation. Nitrogen-fixing bacteria that live on or near the roots oflegumes convert free nitrogen from the air into ammonia in the soil. Nitrifying bacteria thenconvert the ammonia into nitrites and nitrates, which are nutrients used by plants.

FIGURE 1-5. Food chain. Tiny living organisms such asbacteria, algae, microscopic aquatic plants (e.g., phyto-plankton), and microscopic aquatic animals (e.g., zoo-plankton) are eaten by larger animals, which in turn areeaten by still larger animals, etc., until an animal in thechain is consumed by a human. Humans are at the top ofthe food chain.

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Many microbes are essential in various food and bever-age industries, whereas others are used to producecertain enzymes and chemicals (Table 1-2). The useof living organisms or their derivatives to make ormodify useful products or processes is called biotech-nology, an exciting and timely topic that is discussedmore fully in Chapter 10.

Some bacteria and fungi produce antibiotics that areused to treat patients with infectious diseases. By defi-nition, an antibiotic is a substance produced by a mi-crobe that is effective in killing or inhibiting thegrowth of other microbes. The use of microbes in theantibiotic industry is an example of biotechnology.Production of antibiotics by microbes is discussed inChapter 9.

Microbes are essential in the field of genetic engineer-ing. In genetic engineering, a gene or genes from oneorganism (e.g., from a bacterium, a human, an animal,or a plant) is/are inserted into a bacterial or yeast cell.Because a gene contains the instructions for the pro-duction of a gene product (usually a protein), the cellthat receives a new gene can now produce whateverproduct is coded for by that gene; so too can all of thecells that arise from the original cell. Microbiologistshave engineered bacteria and yeasts to produce a vari-ety of useful substances, such as insulin, various typesof growth hormones, interferons, and materials for useas vaccines. Genetic engineering is discussed morefully in Chapter 7.

For many years, microbes have been used as cell mod-els. The more that scientists learned about the struc-ture and functions of microbial cells, the more theylearned about cells in general. The intestinal bacteriumE. coli is one of the most studied of all microbes. Bystudying E. coli, scientists have learned a great deal

about the composition and inner workings of cells, in-cluding human cells.

Finally, we come to diseases.Microbes cause two cate-gories of diseases: infectiousdiseases and microbial intox-ications (Fig. 1-6). An infec-tious disease results when a pathogen colonizes thebody and subsequently causes disease. A microbialintoxication results when a person ingests a toxin (poi-sonous substance) that has been produced by a mi-crobe. Of the two categories, infectious diseases causefar more illnesses and deaths. Infectious diseases are the


CATEGORY EXAMPLES

Foods Acidophilus milk, bread, butter, buttermilk, chocolate, coffee,cottage cheese, cream cheese, fish sauces, green olives, kimchi(from cabbage), meat products (e.g., country-cured hams,sausage, salami), pickles, poi (fermented taro root), sauerkraut,sour cream, sourdough bread, soy sauce, various cheeses (e.g.,cheddar, Swiss, Limburger, Camembert, Roquefort and other bluecheeses), vinegar, yogurt

Alcoholic beverages Ale, beer, brandy, sake (rice wine), rum, sherry, vodka, whiskey, wine

Chemicals Acetic acid, acetone, butanol, citric acid, ethanol, formic acid,glycerol, isopropanol, lactic acid

Antibiotics Amphotericin B, bacitracin, cephalosporins, chloramphenicol, cy-cloheximide, cycloserine, erythromycin, griseofulvin, kanamycin,lincomycin, neomycin, novobiocin, nystatin, penicillin, polymyxinB, streptomycin, tetracycline

Products Requiring Microbial Participationin the Manufacturing Process

TABLE 1-2

Pathogens cause twomajor types of diseases:infectious diseases andmicrobial intoxications.

A pathogen colonizesa persons body.

The pathogencauses a disease.

This type of disease is knownas an infectious disease.

A pathogen producesa toxin in vitro.

Infectious Disease Microbial Intoxication

A person ingests the toxin.The toxin causes a disease.

This type of disease is knownas a microbial intoxication.

FIGURE 1-6. The two categories of diseases causedby pathogens. Infectious diseases result when apathogen colonizes (inhabits) the body and subsequentlycauses disease. Microbial intoxications result when a per-son ingests a toxin (poisonous substance) that has beenproduced by a pathogen in vitro (outside the body).

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leading cause of death in the world and the third lead-ing cause of death in the United States (after heart dis-ease and cancer). Worldwide, infectious diseases causeabout 50,000 deaths per day, with the majority ofdeaths occuring in developing countries. Anyone pur-suing a career in a healthcare profession must be awareof infectious diseases, the pathogens that cause them,the sources of the pathogens, how these diseases aretransmitted, and how to protect yourself and yourpatients from these diseases. Physicians assistants,nurses, surgical technologists, dental assistants, labora-tory technologists, respiratory therapists, orderlies,nurses aides, and all others who are associated with pa-tients and patient care must take precautions to preventthe spread of pathogens. Harmful microbes may betransferred from health workers to patients; from pa-tient to patient; from contaminated mechanical devices,instruments, and syringes to patients; from contami-nated bedding, clothes, dishes, and food to patients;and from patients to healthcare workers, hospital visi-tors, and other susceptible persons. To limit the spreadof pathogens, sterile, aseptic, and antiseptic techniques(discussed in Chapter 12) are used everywhere in hos-pitals, nursing homes, operating rooms, and laborato-ries. In addition, the bioterrorist activities of recentyears serve to remind us that everyone should have anunderstanding of the agents (pathogens) that are in-volved and how to protect ourselves from becoming in-fected. Bioterrorist and biological warfare agents arediscussed in Chapter 11. Additional information aboutmicrobial intoxications can be found in CD-ROMAppendix 1 (Microbial Intoxications).

FIRST MICROORGANISMS ON EARTH

Perhaps you have wondered how long microbes have ex-isted on Earth. Scientists tell us that the Earth was formedabout 4.5 billion years ago and, for the first 800 million to1 billion years of Earths existence, there was no life on thisplanet. Fossils of primitive microbes (as many as 11 differ-ent types) found in ancient rock formations in northwest-ern Australia date back to about 3.5 billion years ago. Bycomparison, animals and humans are relative newcomers.Animals made their appearance on Earth between 900 and650 million years ago (there is some disagreement in thescientific community about the exact date), and, in theirpresent form, humans (Homo sapiens) have existed for onlythe past 100,000 years or so. Candidates for the first mi-crobes on Earth are archaea and cyanobacteria; these typesof microbes are discussed in Chapter 4.

EARLIEST KNOWN INFECTIOUSDISEASES

In all likelihood, infectious diseases of humans and ani-mals have existed for as long as humans and animals have

inhabited the planet. We know that human pathogenshave existed for thousands of years because damagecaused by them has been observed in the bones and inter-nal organs of mummies and early human fossils. Bystudying mummies, scientists have learned that bacterialdiseases, such as tuberculosis and syphilis, and parasiticworm infections, such as schistosomiasis, dracunculiasis(guinea worm infection), and tapeworm infections, havebeen around for a very long time.

The earliest known account of a pestilence oc-curred in Egypt about 3180 BC. This may represent thefirst recorded epidemic, although words like pestilence andplague were used without definition in early writings.Around 1900 BC, near the end of the Trojan War, theGreek army was decimated by an epidemic of what isthought to have been bubonic plague. The Ebers pa-pyrus, describing epidemic fevers, was discovered in atomb in Thebes, Egypt; it was written around 1500 BC. Adisease thought to be smallpox occurred in China around1122 BC. Epidemics of plague occurred in Rome in 790,710, and 640 BC and in Greece around 430 BC.

In addition to the diseases already mentioned, thereare early accounts of rabies, anthrax, dysentery, smallpox,ergotism, botulism, measles, typhoid fever, typhus fever,diphtheria, and syphilis. The syphilis story is quite inter-esting. It made its first appearance in Europe in 1493.Many people believe that syphilis was carried to Europeby Native Americans who were brought to Portugal byChristopher Columbus. The French called syphilis theNeapolitan disease; the Italians called it the French orSpanish disease; and the English called it the French pox.Other names for syphilis were Spanish, German, Polish,and Turkish pocks. The name syphilis was not given tothe disease until 1530.

PIONEERS IN THE SCIENCE OF MICROBIOLOGY

Bacteria and protozoa were the first microbes to be ob-served by humans. It then took about 200 years before aconnection was established between microbes and infec-tious diseases. Among the most significant events in theearly history of microbiology were the development ofmicroscopes, bacterial staining procedures, techniquesthat enabled microorganisms to be cultured (grown) inthe laboratory, and steps that could be taken to provethat specific microbes were responsible for causing spe-cific infectious diseases. During the past 400 years, manyindividuals contributed to our present understanding ofmicrobes. Three early microbiologists are discussed inthis chapter; others are discussed at appropriate pointsthroughout the book.

Anton van Leeuwenhoek (16321723)Because Anton van Leeuwenhoek was the first person tosee live bacteria and protozoa, he is sometimes referredto as the Father of Microbiology, the Father of


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Bacteriology, and the Father of Protozoology.a

Interestingly, Leeuwenhoek was not a trained scientist.At various times in his life, he was a fabric merchant, asurveyor, a wine assayer, and a minor city official inDelft, Holland. As a hobby, he ground tiny glass lenses,which he mounted in small metal frames, thus creatingwhat today are known as single-lens microscopes orsimple microscopes. During his lifetime, he made morethan 500 of these microscopes. Leeuwenhoeks fine art ofgrinding lenses that would magnify an object to 200 to300 times its size was lost at his death because he had nottaught this skill to anyone during his lifetime. In one ofthe hundreds of letters that he sent to the Royal Societyof London, he wrote:

My method for seeing the very smallest animalculesI do not impart to others; nor how to see very manyanimalcules at one time. This I keep for myselfalone.

Apparently, Leeuwenhoek had an unquenchable cu-riosity, as he used his microscopes to examine almostanything he could get his hands on (Fig. 1-7). He exam-

ined scrapings from his teeth, water from ditches andponds, water in which he had soaked peppercorns, blood,sperm, and even his own diarrheal stools. In many ofthese specimens, he observed various tiny living crea-tures, which he called animalcules. Leeuwenhoekrecorded his observations in the form of letters, which hesent to the Royal Society of London. The following pas-sage is an excerpt from one of those letters (Milestones inMicrobiology, edited by Thomas Brock. American Societyfor Microbiology, Washington, DC, 1961):

Tho my teeth are kept usually very clean, neverthe-less when I view them in a Magnifying Glass, I findgrowing between them a little white matter as thickas wetted flower . . . I therefore took some of thisflower and mixt it . . . with pure rain water whereinwere no Animals . . . and then to my great surprizeperceived that the aforesaid matter contained verymany small living Animals, which moved them-selves very extravagantly . . . The number of theseAnimals in the scurf of a mans Teeth, are so manythat I believe they exceed the number of Men in akingdom. For upon the examination of a small par-cel of it, no thicker than a Horse-hair, I found toomany living Animals therein, that I guess theremight have been 1000 in a quantity of matter nobigger than the 1/100 part of a sand.

Leeuwenhoeks letters finally convinced scientists ofthe late 17th century of the existence of microbes.Leeuwenhoek never speculated on their origin, nor didhe associate them with the cause of disease. Such rela-tionships were not established until the work of LouisPasteur and Robert Koch in the late 19th century.

The following quote is from Paul de Kruifs book,Microbe Hunters, Harcourt Brace, 1926:

[Leeuwenhoek] had stolen and peeped into a fantas-tic sub-visible world of little things, creatures thathad lived, had bred, had battled, had died, com-pletely hidden from and unknown to all men fromthe beginning of time. Beasts these were of a kindthat ravaged and annihilated whole races of men tenmillion times larger than they were themselves.Beings these were, more terrible than fire-spittingdragons or hydra-headed monsters. They weresilent assassins that murdered babes in warm cradlesand kings in sheltered places. It was this invisible,insignificant, but implacableand sometimesfriendlyworld that Leeuwenhoek had looked intofor the first time of all men of all countries.

Once scientists became convinced of the existence oftiny creatures that could not be observed with the nakedeye, they began to speculate on their origin. On the basisof observation, many of the scientists of that time believedthat life could develop spontaneously from inanimate


a Although Leeuwenhoek was probably the first person to see live pro-tozoa, he may not have been the first person to observe protozoa. Manyscholars believe that Robert Hooke (1635-1703), an English physician,was the first person to observe and describe microbes, including a fos-silized protozoan and two species of live microfungi.

FIGURE 1-7. Portrait of Anton van Leeuwenhoek byJan Verkolje. (Courtesy of en.wikipedia.org)

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substances, such as decaying corpses, soil, and swampgases. The idea that life can arise spontaneously fromnonliving material is called the theory of spontaneousgeneration or abiogenesis. For more than 2 centuries,from 1650 to 1850, this theory was debated and tested.Following the work of others, Louis Pasteur (discussedlater) and John Tyndall (discussed in Chapter 3) finallydisproved the theory of spontaneous generation andproved that life can only arise from preexisting life. Thisis called the theory of biogenesis, first proposed by aGerman scientist named Rudolf Virchow in 1858. Notethat the theory of biogenesis does not speculate on theorigin of life, a subject that has been discussed and debatedfor hundreds of years.

Louis Pasteur (18221895)Louis Pasteur (Fig. 1-8), a French chemist, madenumerous contributions to the newly emerging fieldof microbiology and, in fact, his contributions are con-sidered by many people to be the foundation of the sci-ence of microbiology and a cornerstone of modernmedicine. Listed below are some of his most significantcontributions:

While attempting to discover why wine becomescontaminated with undesirable substances, Pasteur

discovered what occurs during alcoholic fermentation(discussed in Chapter 7). He also demonstrated thatdifferent types of microbes produce different fermen-tation products. For example, yeasts convert theglucose in grapes to ethyl alcohol (ethanol) by fermen-tation, but certain contaminating bacteria, such asAcetobacter, convert glucose to acetic acid (vinegar) byfermentation, thus, ruining the taste of the wine.

Through his experiments, Pasteur dealt the fatal blowto the theory of spontaneous generation.

Pasteur discovered forms of life that could exist in theabsence of oxygen. He introduced the terms aerobes(organisms that require oxygen) and anaerobes (or-ganisms that do not require oxygen).

Pasteur developed a process (today known as pasteur-ization) to kill microbes that were causing wine tospoilan economic concern to Frances wine industry.Pasteurization can be used to kill pathogens in manytypes of liquids. Pasteurs process involved heatingwine to 55Cb and holding it at that temperature forseveral minutes. Today, pasteurization is accomplishedby heating liquids to 63 to 65C for 30 minutes or to73 to 75C for 15 seconds. It should be noted that pas-teurization does not kill all of the microbes in liquidsjust the pathogens.

Pasteur discovered the infectious agents that causedthe silkworm diseases that were crippling the silk in-dustry in France. He also discovered how to preventsuch diseases.

Pasteur made significant contributions to the germtheory of diseasethe theory that specific microbescause specific infectious diseases. For example, anthraxis caused by a specific bacterium (Bacillus anthracis),whereas tuberculosis is caused by a different bacterium(Mycobacterium tuberculosis).

Pasteur championed changes in hospital practices tominimize the spread of disease by pathogens.

Pasteur developed vaccines to prevent chicken cholera,anthrax, and swine erysipelas (a skin disease). It wasthe development of these vaccines that made him fa-mous in France. Before the vaccines, these diseaseswere decimating chickens, sheep, cattle, and pigs inthat countrya serious economic problem.

Pasteur developed a vaccine to prevent rabies in dogsand successfully used the vaccine to treat human rabies.

To honor Pasteur and continue his work, especiallyin the development of a rabies vaccine, the PasteurInstitute was created in Paris in 1888. It became a clinicfor rabies treatment, a research center for infectious dis-eases, and a teaching center. Many scientists who studiedunder Pasteur went on to make important discoveries of


FIGURE 1-8. Pasteur in his laboratory. A 1925 woodengraving by Timothy Cole. (From Zigrosser C. Medicine andthe Artist [Ars Medica]. New York: Dover Publications, Inc.,1970. By permission of the Philadelphia Museum of Art.)

b C is an abbreviation for Celsius. Although Celsius is also referred toas centigrade, Celsius is preferred. Formulas for converting Celsius toFahrenheit and vice versa can be found in Appendix C (UsefulConversions).

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their own and create a vast international network ofPasteur Institutes. The first of the foreign institutes wasfounded in Saigon, Vietnam, which today is known asHo Chi Minh City. One of the directors of that institutewas Alexandre Emile Jean Yersina former student ofRobert Koch and Louis Pasteurwho, in 1894, discov-ered the bacterium that causes plague.

Robert Koch (18431910)Robert Koch (Fig. 1-9), a German physician, made nu-merous contributions to the science of microbiology.Some of them are listed here:

Koch made many significant contributions to the germtheory of disease. For example, he proved that the an-thrax bacillus (B. anthracis), which had been discoveredearlier by other scientists, was truly the cause of an-thrax. He accomplished this using a series of scientificsteps that he and his colleagues had developed; thesesteps later became known as Kochs Postulates (de-scribed later in this chapter).

Koch discovered that B. anthracis produces spores,capable of resisting adverse conditions.

Koch developed methods of fixing, staining, and pho-tographing bacteria.

Koch developed methods of cultivating bacteria onsolid media. One of Kochs colleagues, R.J. Petri, in-vented a flat glass dish (now known as a Petri dish) inwhich to culture bacteria on solid media. It was FrauHessethe wife of another of Kochs colleagueswhosuggested the use of agar (a polysaccharide obtainedfrom seaweed) as a solidifying agent. These methodsenabled Koch to obtain pure cultures of bacteria. Theterm pure culture refers to a condition in which only

one type of organism is growing on a solid culturemedium or in a liquid culture medium in the labora-tory; no other types of organisms are present.

Koch discovered the bacterium (M. tuberculosis) thatcauses tuberculosis and the bacterium (Vibrio cholerae)that causes cholera.

Kochs work on tuberculin (a protein derived from M.tuberculosis) ultimately led to the development of a skintest valuable in diagnosing tuberculosis.

Kochs PostulatesDuring the mid- to late-1800s, Robert Koch and his col-leagues established an experimental procedure to provethat a specific microbe is the cause of a specific infectiousdisease. This scientific procedure, published in 1884, be-came known as Kochs Postulates (Fig. 1-10).

Kochs Postulates (paraphrased):

1. A particular microbe must be found in all cases of thedisease and must not be present in healthy animals orhumans.

2. The microbe must be isolated from the diseasedanimal or human and grown in pure culture in thelaboratory.


HISTORICAL NOTEAn Ethical Dilemma for Louis PasteurIn July 1885, while he was developing a vaccine thatwould prevent rabies in dogs, Louis Pasteur faced anethical decision. A 9-year-old boy, named JosephMeister, had been bitten 14 times on the legs andhands by a rabid dog. At the time, it was assumed thatvirtually anyone who was bitten by a rabid animalwould die. Meisters mother begged Pasteur to usehis vaccine to save her son. Pasteur was a chemist,not a physician, and thus was not authorized to treathumans. Also, his experimental vaccine had neverbeen administered to a human being. Nonetheless,2 days after the boy had been bitten, Pasteur injectedMeister with the vaccine in an attempt to save theboys life. The boy survived, and Pasteur realizedthat he had developed a rabies vaccine that could beadministered to a person after they had been infectedwith rabies virus.

FIGURE 1-9. Robert Koch. (Courtesy ofwww.wpclipart.com).

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3. The same disease must be produced when microbesfrom the pure culture are inoculated into healthy sus-ceptible laboratory animals.

4. The same microbe must be recovered from the exper-imentally infected animals and grown again in pureculture.

After completing these steps, the microbe is said tohave fulfilled Kochs Postulates and has been proven tobe the cause of that particular infectious disease. KochsPostulates not only helped to prove the germ theory ofdisease, but also gave a tremendous boost to the develop-ment of microbiology by stressing laboratory culture andidentification of microbes.

Exceptions to Kochs PostulatesCircumstances do exist in which Kochs Postulates can-not be fulfilled. Examples of such circumstances are asfollows:

To fulfill Kochs Postulates, it is necessary to grow (cul-ture) the pathogen in the laboratory (in vitroc) in or onartificial culture media. However, certain pathogenswill not grow on artificial media. Such pathogensinclude viruses, rickettsias (a category of bacteria),chlamydias (another category of bacteria), and the bac-teria that cause leprosy and syphilis. Viruses, rickettsias,and chlamydias are called obligate intracellular pathogens(or obligate intracellular parasites) because they canonly survive and multiply within living host cells. Such

organisms can be grown in cell cultures (cultures ofliving human or animal cells of various types), embry-onated chicken eggs, or certain animals (referred to aslaboratory animals). In the laboratory, the leprosybacterium (Mycobacterium leprae) is propagated in ar-madillos, and the spirochetes of syphilis (Treponemapallidum) grow well in the testes of rabbits and chim-panzees. Microbes having complex and demandingnutritional requirements are said to be fastidious(meaning fussy). Although certain fastidious organismscan be grown in the laboratory by adding special mix-tures of vitamins, amino acids, and other nutrients tothe culture media, others cannot be grown in the labo-ratory because no one has discovered what ingredient(s)to add to the medium to enable them to grow.

To fulfill Kochs Postulates, it is necessary to infectlaboratory animals with the pathogen being studied.However, many pathogens are species-specific, mean-ing that they infect only one species of animal. For ex-ample, some pathogens that infect humans will onlyinfect humans. Thus, it is not always possible to finda laboratory animal that can be infected with apathogen that causes human disease. Because humanvolunteers are difficult to obtain and ethical reasonslimit their use, the researcher may only be able toobserve the changes caused by the pathogen in humancells that can be grown in the laboratory (called cellcultures).

Some diseases, called synergistic infections, arecaused not by one particular microbe, but by the com-bined effects of two or more different microbes.Examples of such infections include acute necrotizingulcerative gingivitis (ANUG; also known as trenchmouth) and bacterial vaginosis. It is very difficult toreproduce such synergistic infections in the laboratory.


Sick

Sick

1 2The microorganism must always be found in similarly diseased animals but not in healthy ones.

The microorganism must be isolated from a diseased animal and grown in pure culture.

The isolated microorganism must cause the original disease when inoculated into a susceptible animal.

The microorganism can be reisolated from the experimentally infected animal.

3

4

FIGURE 1-10. Kochs Postulates: proof of the germ theory of disease. (From Harvey RA et al.Lippincotts Illustrated Reviews, Microbiology, 2nd ed. Philadelphia: Lippincott Williams & Wilkins, 2007.)

c As used in this book, the term in vitro refers to something that occursoutside the living body, whereas the term in vivo refers to somethingthat occurs within the living body. In vitro often refers to somethingthat occurs in the laboratory.

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Another difficulty that is sometimes encountered whileattempting to fulfill Kochs Postulates is that certainpathogens become altered when grown in vitro. Somebecome less pathogenic, whereas others become non-pathogenic. Thus, they will no longer infect animalsafter being cultured on artificial media.

It is also important to keepin mind that not all diseasesare caused by microbes. Manydiseases, such as rickets andscurvy, result from dietary de-ficiencies. Some diseases are inherited because of an ab-normality in the chromosomes, as in sickle cell anemia.Others, such as diabetes, result from malfunction of abody organ or system. Still others, such as cancer of thelungs and skin, are influenced by environmental factors.However, all infectious diseases are caused by microbes,as are all microbial intoxications.

CAREERS IN MICROBIOLOGY

A microbiologist is a scientist who studies microbes. Heor she might have a bachelors, masters, or doctoral de-gree in microbiology.

There are many career fields within the science of mi-crobiology. For example, a person may specialize in thestudy of just one particular category of microbes. A bacte-riologist is a scientist who specializes in bacteriologythe study of the structure, functions, and activities ofbacteria. Scientists specializing in the field of phycology(or algology) study the various types of algae and are calledphycologists (or algologists). Protozoologists explorethe area of protozoologythe study of protozoa andtheir activities. Those who specialize in the study of fungi,or mycology, are called mycologists. Virology encom-passes the study of viruses and their effects on living cellsof all types. Virologists and cell biologists may becomegenetic engineers who transfer genetic material (deoxyri-bonucleic acid or DNA) from one cell type to another.Virologists may also study prions and viroids, acellularinfectious agents that are even smaller than viruses (dis-cussed in Chapter 4).

Other career fields in microbiology pertain more toapplied microbiologythat is, how a knowledge of mi-crobiology can be applied to different aspects of society,medicine, and industry. Two medically related careerfields are discussed here; other microbiology career fieldsare discussed on the CD-ROM that accompanies thisbook. The scope of microbiology has broad, far-reachingeffects on humans and their environment.

Medical and Clinical MicrobiologyMedical microbiology is an excellent career field for in-dividuals having interests in medicine and microbiol-ogy. The field of medical microbiology involves thestudy of pathogens, the diseases they cause, and thebodys defenses against disease. This field is concerned

with epidemiology, transmission of pathogens, disease-prevention measures, aseptic techniques, treatment ofinfectious diseases, immunology, and the production ofvaccines to protect people and animals against infec-tious diseases. The complete or almost complete eradi-cation of diseases like smallpox and polio, the safetyof modern surgery, and the successful treatment of vic-tims of infectious diseases are attributable to the manytechnological advances in this field. A branch of medicalmicrobiology, called clinical microbiology or diag-nostic microbiology, is concerned with the laboratorydiagnosis of infectious diseases of humans. This is anexcellent career field for individuals with interests inlaboratory sciences and microbiology. Diagnostic mi-crobiology and the clinical microbiology laboratory arediscussed in Chapter 13.


ON THE CD-ROM Terms Introduced in This Chapter Review of Key Points Insight: Additional Careers in Microbiology Increase Your Knowledge Critical Thinking Additional Self-Assessment Exercises

SELF-ASSESSMENT EXERCISES

After studying this chapter, answer the following multiple-choice questions.

1. Which of the following individuals is considered tobe the Father of Microbiology?a. Anton von Leeuwenhoekb. Louis Pasteurc. Robert Kochd. Rudolf Virchow

2. The microbes that usually live on or in a person arecollectively referred to as:a. germs.b. indigenous microflora.c. nonpathogens.d. opportunistic pathogens.

3. Microbes that live on dead and decaying organicmaterial are known as:a. indigenous microflora.b. parasites.c. pathogens.d. saprophytes.

4. The study of algae is called:a. algaeology.b. botany.c. mycology.d. phycology.

All infectious diseasesand microbialintoxications are causedby microbes.

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5. The field of parasitology involves the study of whichof the following types of organisms?a. arthropods, bacteria, fungi, protozoa, and virusesb. arthropods, helminths, and certain protozoac. bacteria, fungi, and protozoad. bacteria, fungi, and viruses

6. Rudolf Virchow is given credit for proposing whichof the following theories?a. abiogenesisb. biogenesisc. germ theory of diseased. spontaneous generation

7. Which of the following microbes are considered ob-ligate intracellular pathogens?a. chlamydias, rickettsias, M. leprae, and T. pallidumb. M. leprae and T. pallidumc. M. tuberculosis and virusesd. rickettsias, chlamydias, and viruses

8. Which of the following statements is true?a. Koch developed a rabies vaccine.b. Microbes are ubiquitous.c. Most microbes are harmful to humans.d. Pasteur conducted experiments that proved the

theory of abiogenesis.9. Which of the following are even smaller than

viruses?a. chlamydiasb. prions and viroidsc. rickettsiasd. cyanobacteria

10. Which of the following individuals introduced theterms aerobes and anaerobes?a. Anton von Leeuwenhoekb. Louis Pasteurc. Robert Kochd. Rudolf Virchow


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LEARNING OBJECTIVES

AFTER STUDYING THIS CHAPTER, YOU SHOULD BE ABLE TO:

Explain the interrelationships among the following met-ric system units of length: centimeters, millimeters, mi-crometers, and nanometers

State the metric units used to express the sizes of bac-teria, protozoa, and viruses

Compare and contrast the various types of micro-scopes, to include simple microscopes, compound lightmicroscopes, electron microscopes, and atomic forcemicroscopes

INTRODUCTION

Microbes are very tiny. But how tiny are they?Generally, some type of microscope is required to seethem; thus, microbes are said to be microscopic. Varioustypes of microscopes are discussed in this chapter. Themetric system will be discussed first, however, becausemetric system units of length are used to express thesizes of microbes and the resolving power of opticalinstruments.

USING THE METRIC SYSTEM TO EXPRESS THE SIZES OF MICROBES

In microbiology, metric units (primarily micrometersand nanometers) are used to express the sizes of mi-

crobes. The basic unit of length in the metric system, themeter (m), is equivalent to approximately 39.4 inches andis, therefore, about 3.4 inches longer than a yard. A metermay be divided into 10 (101) equally spaced units calleddecimeters; or 100 (102) equally spaced units called cen-timeters; or 1,000 (103) equally spaced units called mil-limeters; or 1 million (106) equally spaced units calledmicrometers; or 1 billion (109) equally spaced unitscalled nanometers. Interrelationships among these unitsare shown in Figure 2-1. Formulas that can be used toconvert inches into centimeters, millimeters, etc., can befound in Appendix C (Useful Conversions) at the backof the book.

It should be noted that the old terms micron ()a andmillimicron (m) have been replaced by the termsmicrometer (m) and nanometer (nm), respectively. Anangstrom () is 0.1 nanometer (0.1 nm). Using this scale,human red blood cells are about 7 m in diameter.

The sizes of bacteria andprotozoa are usually expressedin terms of micrometers. Forexample, a typical sphericalbacterium (coccus; pl., cocci)is approximately 1 m in di-ameter. About seven coccicould fit side by side across a human red blood cell. If thehead of a pin was 1 mm (1,000 m) in diameter, then

13

VIEWING THE MICROBIAL WORLD 2

CHAPTER OUTLINE

INTRODUCTIONUSING THE METRIC SYSTEM

TO EXPRESS THE SIZES OF MICROBES

MICROSCOPESSimple MicroscopesCompound MicroscopesElectron MicroscopesAtomic Force Microscopes

The sizes of bacteria are expressed inmicrometers, whereasthe sizes of viruses areexpressed innanometers.

a The Greek letter is pronounced mew. Greek letters are frequentlyused in science, including the science of microbiology. To aid studentswho are unfamiliar with the Greek alphabet, Appendix D contains thecomplete Greek alphabet.

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1,000 cocci could be placed side by side on the pinhead.A typical rod-shaped bacterium (bacillus; pl., bacilli) isabout 1 m wide 3 m long, although some bacilli areshorter and some form very long filaments. The sizes ofviruses are expressed in terms of nanometers. Most ofthe viruses that cause human disease range in size fromabout 10 to 300 nm, although some (e.g., Ebola virus, acause of hemorrhagic fever) can be as long as 1,000 nm(1 m). Some very large protozoa reach a length of2,000 m (2 mm).

In the microbiology labora-tory, the sizes of cellular mi-crobes are measured using anocular micrometer, a tiny rulerwithin the eyepiece (ocular) ofthe compound light microscope(described later). Before it canbe used to measure objects, however, the ocular microm-eter must first be calibrated, using a measuring devicecalled a stage micrometer. Calibration must be per-formed for each of the objective lenses to determine thedistance between the marks on the ocular micrometer.The ocular micrometer can then be used to measurelengths and widths of microbes and other objects on thespecimen slide. The sizes of some microbes are shown inFigure 2-2 and Table 2-1.

MICROSCOPES

The human eye, a telescope, a pair of binoculars, a mag-nifying glass, and a microscope can all be thought of asvarious types of optical instruments. A microscope is

an optical instrument that is used to observe tiny ob-jects, often objects that cannot be seen at all with theunaided human eye (the naked eye). Each optical in-strument has a limit as to what can be seen using thatinstrument. This limit is referred to as the resolvingpower or resolution of the instrument. Resolvingpower is discussed in more detail later in the chapter.Table 2-2 contains the resolving powers for variousoptical instruments.


An ocular micrometer isused to measure thedimensions of objectsbeing viewed with acompound lightmicroscope.

1 meter

Centimeters

One meter contains

101001,0001,000,0001,000,000,000

= 1 101= 1 102= 1 103= 1 106= 1 109

One centimeter contains

One millimeter contains

One micrometer contains

One nanometer contains

Millimeters Micrometers Nanometers

100 1,000 1,000,000 1,000,000,000

1 10 10,000 10,000,000

1 1,000 1,000,000

1 1,000

1

FIGURE 2-1. Representations ofmetric units of measure and numbers.

FIGURE 2-2. The relative sizes of Staphylococcusand Chlamydia bacteria and several viruses.Poliovirus is one of the smallest viruses that infect hu-mans. (From Winn WC Jr, et al. Konemans Color Atlas andTextbook of Diagnostic Microbiology, 6th ed.Philadelphia: Lippincott Williams & Wilkins, 2006.)

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CHAPTER 2 Viewing the Microbial World 15

MICROBE OR MICROBIAL STRUCTURE DIMENSION(S) APPROXIMATE SIZE (m)

Viruses (most) Diameter 0.010.3

BacteriaCocci (spherical bacteria) Diameter average 1Bacilli (rod-shaped bacteria) Width length average 1 3

Filaments (width) 1

FungiYeasts Diameter 35Septate hyphae (hyphae containing cross-walls) Width 215Aseptate hyphae (hyphae without cross-walls) Width 1030

Pond water protozoaChlamydomonas Length 512Euglena Length 3555Vorticella Length 50145Paramecium Length 180300Volvoxa Diameter 350500Stentora Length (when extended) 1,0002,000

aThese organisms are visible with the unaided human eye.

Relative Sizes of MicrobesTABLE 2-1

RESOLVING USEFULTYPE POWER MAGNIFICATION CHARACTERISTICS

Brightfield 0.2000 m 1,000 Used to observe morphology of microorganisms such as bacteria,protozoa, fungi, and algae in living (unstained) and nonliving(stained) state

Cannot observe microbes less than 0.2 m in diameter or thickness, such as spirochetes and viruses

Darkfield 0.2000 m 1,000 Unstained organisms are observed against a dark backgroundUseful for examining thin spirochetesSlightly more difficult to operate than brightfield

Phase-contrast 0.2000 m 1,000 Can be used to observe unstained living microorganisms

Fluorescence 0.2000 m 1,000 Fluorescent dye attached to organismPrimarily an immunodiagnostic technique (immunofluorescence)Used to detect microbes in cells, tissues, and clinical specimens

Transmission 0.0002 mm 200,000 Specimen is viewed on a screen electron (0.2 nm) Excellent resolutionmicroscope Allows examination of cellular and viral ultrastructure(TEM) Specimen is nonliving

Reveals internal features of thin specimens

Scanning 0.0200 mm 10,000 Specimen is viewed on a screen electron (20 nm) Gives the illusion of depth (three-dimensions)microscope Useful for examining surface features of cells and viruses(SEM) Specimen is nonliving

Resolution is less than that of TEM

Characteristics of Various Types of MicroscopesTABLE 2-2

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Simple MicroscopesA simple microscope is defined as a microscope con-taining only one magnifying lens. Actually, a magnifyingglass could be considered a simple microscope. Imagesseen when using a magnifying glass usually appear about3 to 20 times larger than the objects actual size. Duringthe late 1600s, Anton van Leeuwenhoek, who was dis-cussed in Chapter 1, used simple microscopes to observemany tiny objects, including bacteria and protozoa (Fig.2-3). Because of his unique ability to grind glass lenses,scientists believe that Leeuwenhoeks simple micro-scopes had a maximum magnifying power of about 300(300 times).

Compound MicroscopesA compound microscope is amicroscope that contains morethan one magnifying lens.Although the first person toconstruct and use a compoundmicroscope is not known withcertainty, Hans Jansen and hisson Zacharias are often givencredit for being the first (see the following HistoricalNote). Compound light microscopes usually magnifyobjects about 1,000 times. Photographs taken throughthe lens system of compound microscopes are calledphotomicrographs.

Because visible light (from a built-in light bulb) isused as the source of illumination, the compoundmicroscope is also referred to as a compound light

microscope. It is the wavelength of visible light (approx-imately 0.45 m) that limits the size of objects that canbe seen using the compound light microscope. Whenusing the compound light microscope, objects cannot beseen if they are smaller than half of the wavelength of


FIGURE 2-3. Leeuwenhoeks microscopes. (A) Leeuwenhoeks microscopes were very simpledevices. Each had a tiny glass lens, mounted in a brass plate. The specimen was placed on thesharp point of a brass pin, and two screws were used to adjust the position of the specimen.The entire instrument was about 3 to 4 inches long. It was held very close to the eye.(B) Although his microscopes had a magnifying capability of only around 200 to 300,Leeuwenhoek was able to create remarkable drawings of different types of bacteria that heobserved. (From Volk WA, et al. Essentials of Medical Microbiology, 5th ed. Philadelphia:Lippincott-Raven, 1996.)

HISTORICAL NOTEEarly Compound MicroscopesHans Jansen, an optician in Middleburg, Holland, isoften given credit for developing the first compoundmicroscope, sometime between 1590 and 1595.Although his son, Zacharias, was only a young boy atthe time, Zacharias apparently later took over produc-tion of the Jansen microscopes. The Jansen micro-scopes contained two lenses and achieved magnifica-tions of only 3 to 9. Compound microscopeshaving a three-lens system were later used by MarcelloMalpighi in Italy and Robert Hooke in England, bothof whom published papers between 1660 and 1665 de-scribing their microscopic findings. In his 1665 bookentitled Micrographia, Hooke described a fossilizedshell of a foraminiferana type of protozoanandtwo species of microscopic fungi. Some scientists con-sider these to be the first written descriptions of mi-croorganisms and feel that Hooke (rather thanLeeuwenhoek) should be given credit for discoveringmicrobes. Some early compound microscopes areshown in Figure 2-4.

A simple microscopecontains only onemagnifying lens,whereas a compoundmicroscope containsmore than onemagnifying lens.

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visible light. A compound light microscope is shown inFigure 2-5, and the functions of its various componentsare described in Table 2-3.

The compound light mi-croscopes used in todays labo-ratories contain two magnify-ing lens systems. Within theeyepiece or ocular is a lenscalled the ocular lens; it usu-ally has a magnifying power of10. The second magnifying

lens system is in the objective, which is positioned imme-diately above the object to be viewed. The four objectivesused in most laboratory compound light microscopes are4, 10, 40, and 100 objectives. As shown in Table2-4, total magnification is calculated by multiplying themagnifying power of the ocular (10) by the magnifyingpower of the objective that you are using.

The 4 objective is rarely used in microbiology labo-ratories. Usually, specimens are first observed using the10 objective. Once the specimen is in focus, the high-power or high-dry objective is then swung into position.


FIGURE 2-4. A Leeuwenhoekmicroscope (center),surrounded by examples ofearly compound lightmicroscopes. (Not to scale.)

Total magnification ofthe compound lightmicroscope is calculatedby multiplying themagnifying power ofthe ocular lens by themagnifying power ofthe objective beingused.

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This lens can be used to study algae, protozoa, and otherlarge microorganisms. However, the oil-immersion objec-tive (total magnification 1,000) must be used to studybacteria, because they are so tiny. To use the oil-immersionobjective, a drop of immersion oil must first be placedbetween the specimen and the objective; the immersion oilreduces the scattering of light and ensures that the lightwill enter the oil-immersion lens. The oil-immersion ob-jective cannot be used without immersion oil. The oil is notrequired when using the other objectives.

For optimal observation of the specimen, the lightmust be properly adjusted and focused. The condenser,located beneath the stage, focuses light onto the speci-men, adjusts the amount of light, and shapes the cone oflight entering the objective. Generally, the higher themagnification, the more light that is needed.

As magnification is increased, the amount of lightstriking the object being examined must also be in-creased. There are three correct ways to accomplish this:(a) by opening the iris diaphragm in the condenser, (b) byopening the field diaphragm, and (c) by increasing the in-tensity of light being emitted from the microscopes lightbulb, by turning the rheostat knob clockwise. Turning

the knob that raises and lowers the condenser is an incor-rect way to adjust lighting.

Magnification alone is oflittle value unless the enlargedimage possesses increased detailand clarity. Image clarity de-pends on the microscopes re-solving power (or resolution),which is the ability of the lenssystem to distinguish betweentwo adjacent objects. If two ob-jects are moved closer and closer together, there comes apoint when the objects are so close together that the lenssystem can no longer resolve them as two separate objects(i.e., they are so close together that they appear to be oneobject). That distance between them, at which they ceaseto be seen as separate objects, is referred to as the resolv-ing power of the optical instrument. Knowing theresolving power of an optical instrument also defines thesmallest object that can be seen with that instrument. Forexample, the resolving power of the unaided human eye isapproximately 0.2 mm. Thus, the unaided human eyeis unable to see objects smaller than 0.2 mm in diameter.


Eyepiece (A)

Revolvingnosepiece (B)

Objective lenses (C)

Condenser (F)

Field diaphragm lever (I)On/off switch (J) Base (K)

Fineadjustmentknob (M)

Coarseadjustmentknob (N)

Arm (O)

Binocularbody (P)

Condenser control knob (L)

Stage (D)

Iris diaphragmcontrol arm (E)

Collector lens withfield diaphragm (G)

Rheostat controlknob (H)

FIGURE 2-5. A modern com-pound light microscope.

The resolving power orresolution of an opticalinstrument is its abilityto distinguish betweentwo adjacent objects.The resolving power ofthe unaided human eyeis 0.2 mm.

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COMPONENT LOCATION FUNCTION

(A) Ocular lens (also known At the top of the microscope The ocular lens is an 10 magnifying lensas an eyepiece); a monocularmicroscope has one; a binocularmicroscope (such as shown inFig. 2-5) has two

(B) Revolving nosepiece Above the stage Holds the objective lenses

(C) Objective lenses Held in place above the stage

burton's microbiology for the health sciences 9th ed

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