microbiology test bank

Correct Answer: A

Rationale: Step-by-step rationale: 1. Purple-stained diplococci suggest Gram-positive cocci. 2. Capsule presence is a characteristic of Streptococcus pneumoniae. 3. S. pneumoniae is known to form diplococci arrangements. 4. Therefore, the microorganism most likely present is Streptococcus pneumoniae. Summary: - B: Klebsiella pneumoniae is a Gram-negative rod, not a cocci. - C: Neisseria meningitidis is a Gram-negative diplococcus, not a capsule producer. - D: Escherichia coli is a Gram-negative rod, not a cocci or capsule producer.

Correct Answer: A

Rationale: The correct answer is A: Treponema pallidum. This is because Treponema pallidum is a thin spiral bacteria with 12-14 coils and pointed ends, which matches the description given in the question. Treponema pallidum is the causative agent of syphilis. Choices B, C, and D are incorrect: B: Leptospira - Leptospira is a spiral-shaped bacteria, but it does not have the specific characteristics mentioned in the question. C: Borrelia - Borrelia is another spiral-shaped bacteria, but it does not match the specific features described in the question. D: Spirochaeta - Spirochaeta is a genus of spiral-shaped bacteria, but it does not fit the description of having 12-14 coils and pointed ends as mentioned in the question.

Correct Answer: B

Rationale: The correct answer is B because antigenic drift is not caused by the exchange of genetic information between animal and human influenza viruses. Antigenic drift is actually due to point mutations in the genes that encode for the surface proteins of the virus, leading to small changes in the antigens. These mutations can affect the hemagglutinin of both type A and B influenza viruses, making choices A and C correct. Choice D is incorrect because antigenic drift can occur in both type A and B influenza viruses, with type B being less prone to drift compared to type A.

Correct Answer: B

Rationale: The correct answer is B: Motility. The bacterial flagellum is a whip-like appendage that helps bacteria move by rotating like a propeller. This motility allows bacteria to navigate their environment, find nutrients, and avoid harmful conditions. Choices A, C, and D are incorrect because the bacterial flagellum is not involved in protein synthesis, DNA replication, or spore formation. Protein synthesis occurs in ribosomes, DNA replication takes place in the nucleus or nucleoid, and spore formation is a specialized process involving the production of spores for survival in harsh conditions.

Correct Answer: A

Rationale: Step 1: Chlorhexidine belongs to the group of biguanides, making choice A accurate. Step 2: It is commonly used for disinfection of hands, skin, and mucous membranes. Step 3: It has a broad spectrum of antimicrobial activity, making it widely applicable. Summary: Choice B is incorrect as chlorhexidine is not classified as an alcohol. Choice C is incorrect as chlorhexidine has various applications. Choice D is incorrect as chlorhexidine is generally safe for use with low toxicity.