Download - Cell structure of bacteria and normal flora
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Bacterial Cell StructureA. L. Samer Faisal
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Microbiology
• Agents of human infection:– Bacteria Prokaryotes– Helminthes Eukaryotes– Protozoa Eukaryotes– Fungi Eukaryotes– Viruses Non-
cellular
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• Difference between Eukaryotes and Prokaryotes
• Structure
• Replication
• Nucleic acid
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Earliest Prokaryotes
• Most numerous organisms on Earth
• Include all bacteria• Earliest fossils date 2.5
billion years old
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BACTERIA
• Bacteria are large group of single celled prokaryotic microorganisms
• 10 times as many bacteria cells in the human flora as there are human cell in the body
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Shape of Bacteria
Three basic shapes• Cocci: streptococci, Staphylococci,
Diplococci• Bacilli: E.coli, Klebsiella, Bacillus.• Spirochetes: Treponema, Borrelia
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Bacterial Size • Bacteria range in size from about 0.2 to 5 µm.
• The smallest bacteria (Mycoplasma) are about the same size as the largest viruses (poxviruses) and are the smallest organisms capable of existing outside the host.
• The longest bacteria rods approach the size of some yeasts and human R.B.Cs
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According to staining
• Gram positive Thick peptidoglycan layer and teichoic acid
• Gram negative Thin peptidoglycan layer and
lipopolysaccharide- endotoxin
• Acid fast bacilli Mycolic acid (lipids)
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• Some bacteria are variable in shape
• PLEOMORPHIC----many shaped
• Shape of the bacteria is determined by its rigid cell wall
• The microscopic appearance of bacterium is most important criteria for its identification
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pH requirements• Most grow best at pH of 6.5 to 7.0• Many act as decomposers
recycling nutrients• Some cause disease (Pathogenic)
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The Prokaryote• Structural Components MACROMOLECULE SUBUNIT POSITION IN CELL
PROTEIN Amino Acid Flagella, pili, cell wall, cytoplasmic membrane, ribosomes, cytoplasm
POLYSACCHARIDE Sugar/Carbohydrate Capsule, Inclusions, Cell wall
PHOPHOLIPID Fatty Acid Membranes
NUCLEIC ACID(DNA/RNA)
Nucleotide DNA, Nucleoid, Plasmids, Ribosomes,
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Structural Components
Prokaryotes have 5 essential components• Nucleoid (DNA)• Ribosomes• Cell membrane• Cell wall• Surface layer (Capsule)• Appendages
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Structural Components
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BACTERIAL STRUCTURECOVERING LAYERS
• Cell wall• Peptidoglycan
Sugar back bone with peptide side chains,which are cross linked
Rigidity osmotic protection , site of action of antibiotic, lysozyme degrade.
Outer membrane Gram Negative bacteria
Lipid A
Polysaccharide
Toxic component of endotoxin.Surface antigen.
Surface fiber on Gram Positive bacteria
Teichoic acid Surface antigen
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Protection
• Cell Wall made of Peptidoglycan
• May have a sticky coating called the Capsule for attachment to host or other bacteria
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FUNCTION OF CELL WALL• Maintaining the cell's characteristic shape
• Countering the effects of osmotic pressure
• Providing attachment sites for bacteriophages-teichoic acids
• Providing a rigid platform for surface appendages- flagella, fimbriae
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Peptidoglycan
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COMPARISONProperty Gram Positive Gram Negative
Thickness of wall 20-80 nm 10 nm
Number of layers in wall 1 2
Peptidoglycan content >50% 10-20%
Teichoic acid in wall + -
Lipid and lipoprotein content 0-3% 58%
Protein content 0% 9%Lipopolysaccharide 0 13%Sensitive to penicliiin + - (not as much)
Digested by lysozyme + - (not as much)
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Properties of cell wall
• Gram negative bacteria contains endotoxin---lipopolysaccharide
• Polysaccharides and proteins are antigens• Porin proteins helps entry of hydrophilic
molecules• Teichoic acid are fibers on outer surface of
gram positive ---ability to induces septic shock
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Cell Membrane
• Composed of phospholipid bilayer• FUNCTIONS• Active transport• Energy generation---oxidative phosphorylation• Synthesis of precursors of cell wall• Secretion of enzymes and toxins
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• Infoldings of cell membrane carry on photosynthesis & cellular respiration
• Infoldings called Mesosomes
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MesosomesMESOSOME
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Sticky Bacterial Capsule
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Plasmids
• Molecules of DNA that are found in bacteria separate from the bacterial chromosome.
• A circular molecule only much SMALLER than the genomic DNA
• REPLICATE AUTONOMOUSLY from the genomic chromosome. Often there are MANY PLASMID COPIES present in one cell. Further, a cell may contain SEVERAL DIFFERENT PLASMIDS or it may contain NO PLASMIDS at all. Plasmids generally carry genes that are NOT ESSENTIAL for a cell's survival
• May carry genes for ANTIBIOTIC RESISTANCE
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Transposons
• Transposons are pieces of DNA move from one site to another ---- within or between the DNAs of bacteria plasmid or bacteriophage.
• Nick name as Jumping genes• Genes for one or more (usually more) proteins
imparting resistance to antibiotics. When such a transposon is incorporated in plasmid, it can leave the host cell and move to another. This is the way that the alarming phenomenon of multidrug antibiotic resistance spreads so rapidly.
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Appendages
Flagella: FlagellinFunction: Motility/chemotaxis
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Flagella• Bacteria that are
motile have appendages called flagella
• Attached by Basal Body
• A bacteria can have one or many flagella
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Flagella• Made of Flagellin• Used for Classification• Monotrichous: 1 flagella• Lophotrichous: tuft at
one end• Amphitrichous: tuft at
both ends• Peritrichous: all around
bacteria
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Pili• Short protein appendages PILIN• Smaller than flagella• Adhere bacteria to surfaces• Used in conjugation for Exchange of
genetic information• Aid Flotation by increasing buoyancy
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Pili in Conjugation
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Bacterial Shapes
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Shapes Are Used to Classify• Bacillus: Rod shaped• Coccus: Spherical (round)• Vibrio: Comma shaped with flagella• Spirillum: Spiral shape• Spirochete: wormlike spiral shape
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Grouping of Bacteria
• Diplo- Groups of two• Strepto- chains• Staphylo- Grapelike clusters
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Bacillus and E. coli
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Spirochetes
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ACCORDING TO STAINING
GRAM STAINING
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Crystal violet
Gram's iodine
Decolorise with acetone
Counterstain withe.g. methyl red
Gram-positives appear purple
Gram-negatives appear pink
The Gram Stain
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Gram-positive rods
Gram-negative rods
Gram-positive cocci
Gram-negative cocci
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FORMATION OF BACTERIAL SPORE
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• Found in Gram positive bacteria
• Tough, heat resistant
• Peptidoglycan > Picolinic acid
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Normal Flora• Definition
Normal flora is the mixture of microorganisms (bacteria and fungi) that are regularly found at any anatomical site of human body.
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Symbiotic Relationship
• 1. Mutualistic– Both organisms benefit – “mutually benefical”
• 2. Commensalistic– One organism benefits, the other is neither helped
nor harmed
• 3. Opportunistic– Under normal conditions, microbe does not cause
disease, but if conditions become conducive , it can cause disease
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Mutualistic
• Escherichia coli – Synthesizes Vitamin K & B complex Vitamins
– In return, we provide a warm, moist nutrient rich environment for E. coli
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Commensalistic
• We have no Commensalistic relationships with Bacteria
• If Bacteria are in or on our body, they are either helping us (Microbial Antagonism) or harming us.
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Opportunistic
• Escherichia coli - normally in our digestive tract where it causes no problems, but if it gets into the urinary tract it can become pathogenic.
• Staphylococcus aureus – commonly found in the upper respiratory tract, but if it gets into a wound or a burn it can become pathogenic
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The Three Types of Symbiotic Relationships
Table 14.1
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Normal Microbial Flora
• 1. Resident Flora– Microbes that are always present
• 2. Transient Flora– Microbes that live in or on your body for a period
of time (hours, days, weeks, months) then move on or die off
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Transient Microbiota
• Remain in the body for only hours to months before disappearing
• Found in the same regions as resident microbiota
• Cannot persist in the body…because…– Competition from other microorganisms– Elimination by the body’s defenses cells– Chemical or physical changes in the body
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Sterile tissuesIn a healthy human, the
internal tissues such as:• blood• brain• muscle• cerbrospinal fluid (csf.) are normally free of
microorganisms.
Normal Flora
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Normal Flora• Skin• Eyes (i.e.Cunjunctiva)• Nose (i.e. Respiratory tract)• Mouth (i.e Human Oral
Cavity)• Ears• Urogenetal tract• Elementry tract
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Normal Flora• Resident flora
– Acquired rapidly during & after birth
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Normal Flora• Resident flora
– Reflects age of person
– Changes continuously through out life
– Reflects nutrition of person
– Reflects genetics of person
– Reflects environment of person
– Reflects sex of person
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1. They constitute a protective host defense mechanism by occupying ecological niches.
Importance of The Normal Flora (Advantages)
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Importance of The Normal Flora (Advantages)
2. They produce vitamin B and vitamin K in intestine.
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Importance of The Normal Flora (Advantages)
3.The oral flora contribute to immunity by inducing low levels of circulating and secretory antibodies that may cross react with pathogens.
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Importance of The Normal Flora (Advantages)
4. The oral bacteria flora exert microbial antagonism against nonindigenous species by production of inhibitory fatty acids, peroxides, bacteriocins, etc.
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Importance of The Normal Flora (Advantages)
5. The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species.
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Importance of The Normal Flora (Disadvantages)
1. They can cause disease in the following:a) When individuals become immunocompromised.b) When they change their usual anatomic location.
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Contamination vs. Infection
• Contamination – the mere presence of microbes in or on the body
• Infection – results when the organism has evaded the body’s external defenses, multiplied, and become established in the body
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Portals of Entry
• Sites through which pathogens enter the body
• Four major types– Skin– Mucous membranes– Placenta– Parenteral route
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Skin
• Outer layer of packed, dead, skin cells usually acts as a barrier to pathogens
• Some pathogens can enter through openings or cuts
• Others enter by burrowing into or digesting the outer layers of skin…flesh-eating bacteria
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Mucous Membranes
• Line the body cavities that are open to the environment
• Provides a moist, warm environment that is hospitable to pathogens
• Respiratory tract is the most commonly used site of entry – entry is through the nose, mouth or eyes
• Pathogens able to survive the acidic pH of the stomach may use the gastrointestinal tract as a route of entry
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Some Pathogens that Cross the Placenta
Table 14.3
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Parenteral Route
• Pathogens deposited directly into tissues beneath the skin or mucous membranes
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Infection vs. Disease
• Infection is the invasion of the host by a pathogen
• Disease results only if the invading pathogen alters the normal functions of the body
• Disease is also referred to as morbidity
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Manifestations of Disease
• Symptoms – subjective characteristics of disease felt only by the patient
• Signs – objective manifestations of disease that can be observed or measured by others
• Syndrome – group of symptoms and signs that characterize a disease or abnormal condition
• Asymptomatic, or subclinical, infections lack symptoms but may still have signs of infection
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Etiology
• Study of the cause of disease
• Germ theory of disease – disease caused by infections of pathogenic microorganisms
• Robert Koch developed a set of postulates one must satisfy to prove a particular pathogen causes a particular disease
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