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10 Cards in this Set
- Front
- Back
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A bacterial culture with a starting density of 10/3 cells/ml is incubated in liquid nutrient broth. If the bacteria have both a lag time and a generator time of ten minutes, what will the cell density be at thirty minutes?
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4.0 X 10/3. After a 10 min lag, the bacteria will double in number at 20' and double again by 30'.
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List a component found in the cell wall of gram positive bacteria, but not Gram negative bacteria?
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Teichoic acid. The peptidoglycan in most G+ species is covalently linked to techoic acid(polymer of substituted glycerol units linked by phosphodiester bonds).
Techoic acids are also potent cell surface antigens. |
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Are C. botulinum spores found on raw potatoes?
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Yes. They are generally not killed if the potatoes are baked in foil, which holds in moisture and thus keeps the potatoes surface temperature at 100C(below spore killing temperature). During storage at room temperature in the anarobic environment provided by the foil, spores germinate and toxin forms. heating at 100C would kill most C. botulinum because the bacterium is large in its vulnerable vegaetative state. Heat would inactivate toxins as well.
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A lysogenic bacterium...
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carries a prophage. It carries phage genes in a latent state.(prophage). The presence of a phage can convert certain bacteria to human pathogens, but this is rare.
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Give a true statement regarding plasmids.
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R plasmids carry genes for antibiotic resistance.
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What are plasmids?
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Small, circular supercoiled DNA molecules found in some bacteria. They usually do not carry essential genes, but some plasmids, such as R(resistance) plasmids carry genes codinf for antibiotic resistance.
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What occurs when a temperate bacteriophage enters a state called lysogeny?
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The virus may be integrated into the host genome.
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What is the difference between a lytic and a temperate phage?
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The distinction is made according to life cycle. Lytic phages on entering a bacterium produce phage nucleic acids and proteins, assemble many new phage particles, lyse the cell and release the progeny phage.
Temperate phage penetrate the bacterium and enter a dormant state called lysogeny, where most viral genes are repressed. Bacteria are generally not harmed. Phage lambda become integrated into the host genome as prophages. |
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A 32 yr old woman became ill 4 days after the onset of her menstrual period. She presented in the emergency room with fever(104F, elevated WBC(16,000/mm3(normal 4-10,000) and a rash on her trunk and legs. She suffered from fatigue and vomiting and diarrhea. She recently ate at a fast food restaurant, but normally prepared all her meals at home.She most likely has....
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Toxic shock syndrome.
Toxic shock syndrome is caused by overproduction of TSST-1 toxin by colonizing S. aureus triggered by something in hyperabsorbent tampons. many signs are the result of superantigen activity of TSST, which activates a whole subclass of T cells, causing overproduction of cytokines. |
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A 57 yr old man arrives at the emergency room complaining of weakness, fatigue and intermittent fever that has recurred for several weeks. The patient had a cardiac valvular prosthesis implaned 5 years earlier. Physical exam reveals petecchiae on the chest and stomach. Blood cultures grew catalase positive, coagulase negative cocci. They failed to ferment mannitol and growth was inhibited by novobiocin. What is the likely agent?
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Staph. epidermidis. This patient is likely suffering from bacterial endocarditis caused by Staph. epidermidis of the prosthetic heart valve.
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