Lecture 3 - Bacteria

8/13/2019 Lecture 3 - Bacteria

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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

Lecture 3 - Bacteria

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