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The generation time of Escherichia Coli is:
- A. 20 minutes
- B. 60 minutes
- C. 20 hours
- D. 24 hours
Correct Answer: A
Rationale: The correct answer is A: 20 minutes. Escherichia coli has a short generation time, typically around 20 minutes. This means that under ideal conditions, one bacterium can divide and produce two daughter cells every 20 minutes. This rapid growth rate is a characteristic of E. coli and is important in various fields such as microbiology and biotechnology. Choice B (60 minutes) and Choice C (20 hours) are incorrect as they do not align with the typical generation time of E. coli. Choice D (24 hours) is also incorrect as it is too long for the generation time of E. coli.
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Bacteria that use organic compounds as the source of both carbon and energy are referred to as:
- A. photoautotrophs
- B. chemoautotrophs
- C. photoheterotrophs
- D. chemoheterotrophs
Correct Answer: D
Rationale: The correct answer is D: chemoheterotrophs. Chemoheterotrophs use organic compounds as both their carbon source and energy source. They obtain energy by breaking down organic molecules through cellular respiration. Photoautotrophs (A) use light energy to produce organic compounds, chemoautotrophs (B) use inorganic compounds for energy, and photoheterotrophs (C) use light energy but require organic compounds as a carbon source. Therefore, chemoheterotrophs best describe bacteria that obtain both carbon and energy from organic compounds.
A bacteriological laboratory has received smears from the sputum of a patient with a chronic pulmonary disease. Microscopical examination of the smears stained by the Ziehl-Neelsen technique revealed red bacilli. What property of the tuberculosis bacillus has shown itself?
- A. Acid resistance
- B. Alkali resistance
- C. Alcohol resistance
- D. Capsule formation
Correct Answer: A
Rationale: The correct answer is A: Acid resistance. The Ziehl-Neelsen staining technique is specifically used to detect acid-fast bacteria like Mycobacterium tuberculosis, which is resistant to acid decolorization. This property allows the tuberculosis bacillus to retain the stain even after exposure to acid-alcohol, appearing red under the microscope.
Explanation of incorrect choices:
B: Alkali resistance - This property is not relevant in the context of Ziehl-Neelsen staining for acid-fast bacteria.
C: Alcohol resistance - While alcohol resistance is related to acid-fastness, it is not the specific property highlighted by Ziehl-Neelsen staining.
D: Capsule formation - Capsule formation is a different characteristic and not directly related to the staining behavior of acid-fast bacteria in the Ziehl-Neelsen technique.
Autoclaving will usually destroy/inactivate all fungi, bacteria, viruses, and most bacterial spores but will not necessarily eliminate
- A. neurotoxins.
- B. prions.
- C. protozoan cysts.
- D. mycoplasmas.
Correct Answer: B
Rationale: The correct answer is B: prions. Autoclaving, a method of sterilization using high pressure and steam, is effective at destroying most microorganisms including fungi, bacteria, viruses, and most bacterial spores due to denaturation of their proteins and nucleic acids. However, prions are highly resistant infectious proteins that are not easily eliminated by autoclaving. Prions can withstand high temperatures and pressure, making them a challenge to eradicate. Neurotoxins (A), protozoan cysts (C), and mycoplasmas (D) are susceptible to autoclaving and would be destroyed during the process.
Which of the following bacteria is capable of producing an endotoxin that can lead to septic shock?
- A. Escherichia coli
- B. Salmonella enterica
- C. Pseudomonas aeruginosa
- D. All of the above
Correct Answer: D
Rationale: The correct answer is D: All of the above.
1. Escherichia coli can produce endotoxin due to its lipopolysaccharide component.
2. Salmonella enterica also produces endotoxin as part of its cell wall structure.
3. Pseudomonas aeruginosa is known to produce endotoxin as well.
Therefore, all of these bacteria are capable of producing endotoxin, which can trigger an excessive immune response leading to septic shock. Other choices are incorrect because they do not cover all the bacteria mentioned in the question that are capable of producing endotoxin.
Gram-negative rods producing red colonies on Endo agar were isolated from a fecal sample. The bacteria were lactose-fermenting. What microorganism is likely responsible?
- A. Escherichia coli
- B. Salmonella
- C. Shigella
- D. Proteus
Correct Answer: A
Rationale: The correct answer is A: Escherichia coli. E. coli is a Gram-negative rod that ferments lactose, leading to red colonies on Endo agar. This bacterium is commonly found in the human gut and is known for its ability to ferment lactose. Salmonella and Shigella are also Gram-negative rods but do not ferment lactose, so they would not produce red colonies on Endo agar. Proteus is a Gram-negative rod that is not known for its lactose-fermenting ability and would not produce red colonies on Endo agar. Therefore, based on the characteristics provided, E. coli is the most likely microorganism responsible for the red colonies on Endo agar.