microbiology test bank

Correct Answer: D

Rationale: The correct answer is D: Binary fission. Binary fission is a method of bacterial cell division, not a method of acquiring genetic material. Transformation, conjugation, and transduction are mechanisms through which bacteria can acquire genetic material from other sources. Transformation involves the uptake of naked DNA from the environment, conjugation is the transfer of genetic material through direct cell-to-cell contact, and transduction is the transfer of genetic material via bacteriophages. Therefore, binary fission is the only option that does not involve the acquisition of new genetic material.

Correct Answer: C

Rationale: The correct answer is C because hemagglutinin of influenza viruses serves as an attachment molecule to the receptor of the target cell, facilitating viral entry. This is crucial for the virus to infect host cells. Choice A is incorrect because hemagglutinin is not part of the viral capsid but rather a surface protein. Choice B is incorrect as hemagglutinin is not directly involved in viral replication, but in host cell attachment. Choice D is incorrect as hemagglutinin is highly antigenic, triggering the host's immune response.

Correct Answer: A

Rationale: The correct answer is A: Nitrogen-fixing bacteria. These bacteria can convert atmospheric nitrogen into a form that plants can use, promoting plant growth. Denitrifying bacteria (B) convert nitrates back into atmospheric nitrogen. Photosynthetic bacteria (C) use photosynthesis to produce energy and don't fix nitrogen. Fermentative bacteria (D) break down organic compounds without fixing nitrogen. In summary, only nitrogen-fixing bacteria (A) play a crucial role in the nitrogen cycle by converting atmospheric nitrogen into a usable form for plants.

Correct Answer: A

Rationale: Rationale: A: Early application of gentamicin is not recommended as a specific treatment for C. difficile-associated post antibiotic diarrhea because it does not have efficacy against C. difficile. B: Metronidazole is recommended as first-line treatment for mild to moderate C. difficile infection. C: Stopping antibiotic treatment and observing the clinical response for 48 hours is not a recommended strategy as prompt treatment is crucial in C. difficile infection. D: Vancomycin per os is an appropriate treatment for severe C. difficile infection. In summary, A is incorrect because gentamicin is not effective against C. difficile, while B, C, and D are potential treatment strategies based on severity of the infection.

Correct Answer: B

Rationale: Fimbriae in bacteria are hair-like appendages that help in adhesion to surfaces. This is essential for colonization and infection. Fimbriae do not provide motility (flagella do), facilitate protein synthesis (ribosomes do), or help in endospore formation (specialized structures do). Adhesion is the primary function of fimbriae, allowing bacteria to stick to host cells or abiotic surfaces.