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The Bacteria
Dr. Linroy Christian
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Bacteria
Bacteria are typical prokaryotes
Bacteria come in many shapes:
Spherical or ovoid shaped bacteria are referred to as cocci
(singular,coccus
)
Cylindrical shaped bacteria are referred to as rods
Some rods are curved forming a spiral-shaped pattern
called spirilla
Some may be coiled(spirochetes) many variations in bacterial shapes occur
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Cocci Chains (eg. Streptococcus
species)
Clusters (eg. Staphylococcus
species)
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Rods
Typical rod (eg. Bacillus) Some rods may have spores
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Spiral-shaped Bacteria
Spirillum (eg., Spirillum volutans) Spirochete (eg. Treponemapallidum and leptospira)
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Bacterial Structure
Cell Wall Made of peptidoglycan
Rigid material
Thicker in gram positive bacteria than gram
negative bacteria
Peptidoglycan absent in some bacteria
Cell Membrane
An inner membrane
Made of protein and lipids
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Bacterial Structure
Lipopolysaccharide (LPS) An outer membrane
Present in gram negative bacteria, absent in gram
positive bacteria
Capsules
Starchy or gelatinous
Protects cell from phagocytosis
Slime
Loose polysaccharide
Aids in adherence of bacteria to surfaces
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Bacterial Structure Flagella
Thin appendage made of protein
Often longer than the cell
Acts like a propeller
Fimbriae Shorter than flagella
May be used in adherence to surfaces
Not present in all bacteria
Pilli
Similar to fimbriae, but slightly longer
May be involved in mating
Aids in attachment to human tissue
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Bacterial Structure
DNA
Single chromosome
Free in cytoplasm
No nuclear membrane
Plasmids
Circular DNA molecule
Confers special traits
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Gram Positive vs. Gram Negative
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Bacterial Cell
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Bacterial Structure
Endospores
Highly resistant to temperature and disinfectants
Develop when bacteria are exposed to adverse
conditions
Spherical or ovoid
Position within the cell differs within species
Remain viable for years and germinate whenconditions are favourable
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Endospore-forming Bacteria
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Atypical Bacteria
Mycoplasma and Ureaplasma
Lack peptidoglycan
Very small and variable shape
Many are parasitic
Chlamydia Resemble gram negative bacteria
Lack some metabolic enzymes
Can only multiply within a host cell
Rickettsia
Small, gram negative
Multiply within host cell
Cause diseases in humans
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Bacterial Replication