medical microbiology test bank

Correct Answer: C

Rationale: The correct answer is C: Polar placement of volutin granules. This feature is indicative of Corynebacterium diphtheria. Volutin granules are metachromatic granules found in the polar region of the bacterial cell, which is characteristic of this species. This feature helps differentiate it from other bacteria. Explanation: A: Fence-like position of the agent's cells is not a specific morphologic feature of Corynebacterium diphtheria. B: Spores that exceed cells in diameter is not a characteristic feature of Corynebacterium diphtheria. D: Presence of the capsule is not a distinguishing morphologic feature of Corynebacterium diphtheria. In summary, the polar placement of volutin granules is the most indicative feature for determining the type of agent as Corynebacterium diphtheria, making it the correct choice.

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. Clostridium tetani is responsible for causing tetanus due to its production of tetanospasmin toxin. This neurotoxin leads to muscle stiffness and spasms characteristic of tetanus. Clostridium perfringens is associated with gas gangrene, not tetanus. Streptococcus pyogenes causes strep throat and skin infections, not tetanus. Escherichia coli is a common gut bacteria and is not responsible for tetanus. Therefore, choice A is the correct answer for causing tetanus.

Correct Answer: D

Rationale: The correct answer is D because all of these symptoms are early signs of rabies. A short period of depression, nausea, and restlessness are common initial symptoms of rabies infection. These symptoms may be followed by more severe manifestations, such as aggression, confusion, and difficulty swallowing. Therefore, option D is the correct choice as it encompasses all the early symptoms of rabies. Options A, B, and C are incorrect as they focus on individual symptoms, whereas rabies typically presents with a combination of these early signs.

Correct Answer: A

Rationale: The correct answer is A. Method of Ziel-Neelsen. This method uses a special stain (carbol fuchsin) to detect acid-fast organisms like Mycobacterium tuberculosis, the causative agent of tuberculosis. The staining procedure involves heating the slide to help penetrate the mycolic acid layer of the bacteria, making them resistant to decolorization by acid-alcohol. The red stained acid-fast bacilli stand out against the blue counterstain. This method is specific for identifying tubercle bacilli in sputum samples. Choice B: Method of Romanowsky-Giemsa is used for staining blood smears and is not suitable for detecting acid-fast bacilli in sputum. Choice C: Method of Gram is used for staining bacteria based on their cell wall composition and is not effective for identifying acid-fast bacilli like Mycobacterium tuberculosis. Choice D: Method of Neisser is not a specific staining method for acid-fast bacilli and is not suitable

Correct Answer: A

Rationale: The correct answer is A: Capsule. The capsule is a mucous structure tightly bound to the bacterial cell wall. It helps bacteria evade the host immune system and provides protection. The other choices are incorrect because: B) Spores are resistant structures formed by some bacteria for survival, C) Flagella are long, whip-like structures for movement, and D) Filaments are long, thin structures found in some bacteria.