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15 Cards in this Set
- Front
- Back
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What are flagella?
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They are protein filaments that extend like long tails from the cell membranes of certain G+ and G- bacteria. They give the bacteria motility.
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How is the flagellum attached to the bacteria?
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It is affixed by a basal body. This body spans through the entire cell wall, binding to the inner and outer cell membrane in G- bacteria, and to the inner membrane in G+ bugs.
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What type of flagella are found on bacteria?
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They may have a single polar flagellum, as is found on Vibrio cholerae, or many(peritrichous)all around the cell, as is the case with E.coli and Proteus mirabilis. Shigella do not possess flagella.
A single flagellum at either pole of the organism is referred to as amphitrichous. |
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What are pili?
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Pili(fimbriae) are straight filaments arising from the bacterial cell wall. They are shorter than flagella, yet do not move. They can serve as adherence factors, and are called adhesins.
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Give some examples of bacterial pili.
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Neisseria gonorrhea has pili that allow it to bind to cervical cells and buccal cells to cause gonorrhea. E. coli and campylobacter jejuni cannot cause diarrhea without their adhesins to bind to the intestinal epithelium, and Bordetella pertussis uses its adhesins to bind to ciliated respiratory cells and cause whooping cough.
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What is a bacterial capsule?
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They are protective walls that surround the cell membranes of G+ and G- bacteria. They are composed of simple sugar residues. Bacteria secrete these sugar moieties which then coat their outer cell. Bacillis anthracis however has a capsule made up of amino acid residues.
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What benefit do capsules confer?
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They enable bacteria to be more virulent b/c macrophages and neutrophiles are unable to phagocytize the encapsulated organisms.
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Briefly describe some medium physical characteristics of S. pneumoniae.
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Strep. pneumoniae have a capsule. When grown on media, these encapsulated bacteria appear as smooth(S) colonies that cause rapid death when injected into mice. Some strep however, do not have capsules and appear as rough(R) colonies on agar. Rough colonies have lost their virulence.
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List 2 imporatnt tests that enable doctors to visualize capsules under the microscope.
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1. India ink stain- because this stain is not taken up by the capsule, the capsule appears as a transparant halo around the cell. The fungus Cryptococcus is identified this way.
2. Quellung reaction- bacteria are mixed with antibodies that bind to the capsule. When they bind, the capsule swells with water, and becomes microscopically visible. |
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What is capsule opsonization?
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Antibodies directed agaist bacterial capsules protect us as they help our macrophages and neutrophils bind to and eat the encapsulated bacteria. This binding of antibodies binding to the capsule is called opsonization.
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What occurs once the antibodies have bound to the bacterial capsule?
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The macrophage or neutrophil can then bind to the Fc portion of the antibody and gobble up the bacteria.
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Are there capsular vaccines?
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Yes. A vaccine agaist strep pneumoniae has antigens from the 23 most common types of capsules. Immunization with this vaccine elicits an immune response against the capsular antigens and the production of antibodies that protects the individual against future infections by this organism.
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Endospores are formed by which 2 genera of bacteria?
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Both are G+. Bacillus, which is aerobic, and clostridium, which is anaerobic.
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What are endospores?
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They are metabolically dormant forms of bacteria that are resistant to heat, cold, drying and chemical agents; Their protective coat consists of;
A cell membrane Thick peptidoglycan mesh Another cell membrane A wall of keritan like protein An outer layer called the exosporium |
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Why do spores form?
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They form when there is a shortage of needed nutrients and can lie dormant for years. Surgical instruments are heated in an autoclave, which uses steam under pressure, to 121C for 15min in order to ensure the destruction of clostridium and bacillus spores.When it is exposed to a favorable nutrient, it becomes active again.
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