Correct Answer: D

Rationale: The correct answer is D: metronidazole. Metronidazole is specifically effective against protozoan infections due to its ability to target and disrupt the DNA of the parasites. It is commonly used to treat infections such as trichomoniasis and giardiasis that affect the reproductive system. Ampicillin (A) and tetracycline (B) are antibiotics that target bacteria, not protozoa. Ciprofloxacin (C) is also an antibiotic that is effective against certain bacterial infections but not protozoan infections. Therefore, metronidazole is the most appropriate choice for fighting protozoan infections of the reproductive system.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent for pneumonia in this case due to the presence of Gram-positive cocci in pairs with a capsule, which is a typical characteristic of S. pneumoniae. This pathogen is a common cause of community-acquired pneumonia and is known for its encapsulated morphology. Staphylococcus aureus (B) is a Gram-positive cocci but does not typically present in pairs with a capsule in pneumonia cases. Klebsiella pneumoniae (C) is a Gram-negative bacterium and does not match the description provided. Pseudomonas aeruginosa (D) is a Gram-negative bacterium that is not typically associated with Gram-positive cocci in pneumonia samples.

Correct Answer: A

Rationale: The correct answer is A: Type IV hypersensitivity reaction. This type of reaction is characterized by a delayed response involving T cells. In this case, the appearance of a papule after 48 hours indicates a delayed hypersensitivity reaction, which is typical of a Type IV reaction. The other choices are incorrect because: B: Arthus phenomenon is a localized immune complex-mediated reaction, not seen in tuberculin tests. C: Seroreaction typically involves antibodies reacting with soluble antigens, not seen in this scenario. D: Type II hypersensitivity reactions involve antibodies targeting specific cells or tissues, which is not the mechanism at play in this case.

Correct Answer: C

Rationale: The correct answer is C: It is non-motile and non-spore forming. Pseudomonas aeruginosa is motile due to its flagella and is non-spore forming. A is correct because it is a Gram-negative bacterium, and B is correct as it is oxidase-positive. D is incorrect because C is not true.

Correct Answer: A

Rationale: Step 1: Mycobacterium leprae is the bacterium responsible for causing leprosy, a chronic infectious disease affecting the skin and nerves. Step 2: Neisseria gonorrhoeae causes gonorrhea, a sexually transmitted infection. Step 3: Streptococcus pneumoniae causes pneumonia and other respiratory infections. Step 4: Clostridium perfringens causes gas gangrene and food poisoning. Summary: A is correct as Mycobacterium leprae specifically causes leprosy, while B, C, and D cause different diseases unrelated to leprosy.