Correct Answer: C

Rationale: The correct answer is C: Inhibits protein synthesis. Exotoxin of C. Diphtheriae acts by inhibiting protein synthesis in host cells. This disrupts cellular functions and leads to tissue damage. Choice A is incorrect because acetylcholine release is not affected. Choice B is incorrect as it does not involve neurotransmitters. Choice D is incorrect as the exotoxin does have a specific mechanism.

Correct Answer: A

Rationale: The correct answer is A: Mantoux test. The Mantoux test is used to detect tuberculosis infection by injecting a small amount of tuberculin under the skin and checking for a reaction. This test helps identify individuals who have been exposed to tuberculosis. The other choices are incorrect because: B: Schick test is used to determine immunity to diphtheria, not tuberculosis. C: Anthraxine test is used for anthrax, not tuberculosis. D: Burnet test is not a recognized medical test for tuberculosis.

Correct Answer: B

Rationale: The correct answer is B: Agglutination reaction. This is the most suitable serological reaction for the quick determination of the antigen of the epizootic agent causing mass rodent deaths. In agglutination reaction, antibodies cause the clumping of antigens, allowing for easy visual detection of the presence of the specific antigen. This is efficient for rapid diagnosis in cases of suspected infectious diseases like plague. A: Precipitation reaction is more suitable for identifying soluble antigens, not for quick determination of a specific antigen in this scenario. C: Reaction of passive hemagglutination is used for measuring the presence of antibodies, not antigens. D: Bordet-Gengou test is a specific test for the identification of Bordetella pertussis bacterium, not suitable for this scenario.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. 1. Gram-positive diplococci with pointed ends: characteristic morphology of Streptococcus pneumoniae. 2. Surrounded by a capsule: S. pneumoniae is encapsulated, important for virulence. 3. Klebsiella pneumoniae (B) is a Gram-negative rod, Neisseria meningitidis (C) is a Gram-negative diplococcus, and Staphylococcus aureus (D) is a Gram-positive cocci in clusters, not diplococci.

Correct Answer: A

Rationale: Step 1: Trichomonal gingivostomatitis is caused by the parasite Trichomonas tenax. Step 2: Metronidazole is the drug of choice for treating infections caused by anaerobic organisms like Trichomonas. Step 3: Metronidazole effectively targets and eliminates Trichomonas parasites in the oral cavity. Step 4: Therefore, the correct drug choice for treating trichomonal gingivostomatitis is Metronidazole. Summary: - Ampicillin (B) is an antibiotic effective against Gram-positive bacteria, not parasites. - Gentamicin sulfate (C) is an antibiotic used for bacterial infections, not parasitic infections. - Nystatin (D) is an antifungal medication used for treating fungal infections, not parasitic infections like trichomonal gingivostomatitis.