Clinical Mycology

Distribution of microorganisms

Air

Soil

Water

Animals

Human body

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Microbes are involved in

nutrient production & energy flow

decomposition

production of foods, drugs & vaccines

bioremediation

causing disease

Microorganisms and Human Beings

Beneficial activities: Most microbes are of benefit to human beings, some are necessary( nitrogen, carbon cycles, etc)

Harmful activities: A portion of microbes cause diseases and are poisonous to human, and these are really that concern us in the study of medical microbiology, etc.

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Impact of pathogens

Nearly 2,000 different microbes cause diseases

10 B infections/year worldwide

13 M deaths from infections/year worldwide

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Characteristics of microbes

Archea

Bacteria

Eukaria

Domain Kingdom

Planta

Animalia

Mycota

(Mycetae)

Classification of Fungi

Comparison of fungi and bacteriafeature fungi bacteria

diameter 4um 1um

nucleus Eukaryotic prokaryotic

cytoplasm Mitochondria and endoplasmic reticulum present

Mitochondria and endoplasmic reticulum present

Cell membrane Sterols present Sterols absent

Cell wall chitin peptidoglycan

spores Sexual and asexual spores for reproduction

Endospores for survival, not for reproduction

Thermal dimorphism

yes No

metabolism Require organic carbon; no obligate anaerobes

May do not require organic carbon; many obligate anaerobes

Characteristics of fungi

A. eukaryotic, non- vascular organisms

B. reproduce by means of spores (conidia), usually wind-disseminated

C. both sexual (meiotic) and asexual (mitotic) spores may be produced, depending on the species and conditions

D. typically not motile, although a few (e.g. Chytrids) have a motile phase.

E. like plants, may have a stable haploid & diploid states

F. vegetative body may be unicellular (yeasts) or multicellular moulds composed of microscopic threads called hyphae.

G. cell walls composed of mostly of chitin and glucan.

More Characteristics of Fungi

H. fungi are heterotrophic ( “other feeding,” must feed on preformed organic material), not autotrophic ( “self feeding,” make their own food by photosynthesis).

- Unlike animals (also heterotrophic), which ingest then digest, fungi digest then ingest. -Fungi produce exoenzymes to accomplish this

I. Most fungi store their food as glycogen (like animals). Plants store food as starch.

K. Fungal cell membranes have a unique sterol, ergosterol, which replaces cholesterol found in mammalian cell membranes

L. Tubule protein—production of a different type in microtubules formed during nuclear division.

Dimorphism

Many pathogenic fungi are dimorphic, forming moulds at ambient temperatures but yeasts at body temperature.

Structure of fungi

Morphology

Unicellular fungiMulticellular fungi Hypha: mycelium (vegetative, aerial or reproductive). Spores: asexual spore a) Conidium:

macroconidium, microconidium. b) Thallospore:

blastospore, chlamydospore, arthrospore c) Sporangiospore

Fungal Morphology

Yeast

Hyphae (threads) making up a mycelium

Mould

Encapsulated yeastCryptococcus neoformans

Multicellular fungi

Hypha

•spore

Hypha

Unicel lular fungiUnicel lular

fungi

Medically important fungi

Includes 4 phyla

Ascomycota Sexual reproduction in a sack called an ascus with the production of ascopspores.

Basidiomycota Sexual reproduction in a sack called a basidium with the production of basidiospores.

Zygomycota Sexual reproduction by gametes and asexual reproduction with the formation of zygospores.

Mitosporic Fungi （ Fungi Imperfecti) ， No recognizable form of sexual reproduction. Includes most pathogenic fungi.

Deutemycotina

Ascomycotina Basidiomycotina

Zygomycotina

Dimorphism

Germ theory of disease

Many diseases are caused by the growth of microbes in the body

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Robert Koch

Established a sequence of experimental steps to show that a specific m.o. causes a particular disease.

Developed pure culture methods.

Identified cause of anthrax, TB, & cholera.

(1843-1910)

Koch’s postulates

The microbe must be found in the body in all cases of the disease It must be isolated from a case and grown in a series of pure culture in vitro It reproduce the disease on the inoculation of a late pure culture into a susceptible animal The microbe must be isolated again into pure culture from such experimentally caused infection.

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Taxonomy - system for organizing, classifying & naming living things

Domain - Archaea, Bacteria & EukaryaKingdom - 5Phylum or DivisionClass OrderFamilyGenusspecies

Culture

Sabouraud culture mediumoptimal pH 4-6optimal temperature 22-28 C some deep pathogenic fungi need 37 C, Aerobictypes of colonies– yeast, filamentousMultiplication:budding, hypha formation, branching or disruption of hypha, spore formation

Resistance

Resistant to dry, sunlight, UV light and many chemicals

Sensitive to wet heat

four types of mycotic diseases:

Hypersensitivity - an allergic reaction to molds and spores.Mycotoxicoses - poisoning of man and animals by feeds and food products contaminated by fungi which produce toxins from the grain substrate.Mycotoxin and tumorMycetismus - the ingestion of toxin (mushroom poisoning).

Infection

Immunity

Nonspecific immunitySpecific immunity

DIAGNOSIS1. Skin scrapings suspected to contain dermatophytes or pus from a lesion can be mounted in KOH on a slide and examined directly under the microscope.2. Skin testing (dermal hypersensitivity) used to be popular as a diagnostic tool. 3. Serology may be helpful when it is applied to a specific fungal disease.4. Direct fluorescent microscopy.5. Biopsy and histopathology.  6. Culture. Pathogenic fungi are usually grown on Sabouraud dextrose agar . It has a slightly acidic pH (~5.6); cyclohexamide, penicillin, streptomycin or other inhibitory antibiotics are often added to prevent bacterial contamination and overgrowth.