Correct Answer: A

Rationale: The correct answer is A: Hyperresponsiveness reaction type IV. This type of reaction, also known as delayed-type hypersensitivity, is characterized by the activation of T lymphocytes and macrophages, leading to inflammation at the site of antigen exposure. In the case of the Mantoux test, the appearance of a papule 48 hours later indicates a delayed hypersensitivity reaction mediated by T cells. Choice B: Reaction of Arthus phenomenon type is incorrect as this type of reaction involves immune complexes forming in the blood vessels leading to tissue damage, which is not the mechanism seen in the Mantoux test reaction. Choice C: Reaction of serum sickness type is incorrect as this type of reaction involves the formation of immune complexes in the blood leading to systemic symptoms like fever, rash, and joint pain, which is not typically seen in the Mantoux test reaction. Choice D: Atopic reaction is incorrect as atopic reactions involve IgE antibodies and mast cell degranulation, which are not the mechanisms

Correct Answer: A

Rationale: The correct answer is A: Toxoplasmosis. Toxoplasmosis is a parasitic infection caused by Toxoplasma gondii, which can be transmitted from mother to fetus during pregnancy, leading to congenital toxoplasmosis. This infection can result in stillbirth, multiple developmental defects, and intrauterine death. Leishmaniasis (B), Malaria (C), and Amebiasis (D) are caused by different parasites and do not typically lead to intrauterine death or developmental defects in the fetus.

Correct Answer: B

Rationale: The correct answer is B: Vibrio cholerae. Cholera is caused by this specific bacterium due to its production of cholera toxin, leading to severe watery diarrhea. Shigella dysenteriae causes dysentery, Salmonella enterica causes salmonellosis, and Clostridium perfringens causes food poisoning, none of which present with the characteristic symptoms of cholera.

Correct Answer: B

Rationale: The correct answer is B: Mycobacterium leprae. This microorganism can only be cultured in the footpads of mice or a species of armadillo due to its specific growth requirements. Mycobacterium tuberculosis (choice A) can be cultured in various culture media in the laboratory. Neisseria gonorrhoeae (choice C) can be cultured on selective media like Thayer-Martin agar. Mycoplasma (choice D) can be cultured in cell cultures or specialized media. Therefore, the unique growth pattern of Mycobacterium leprae makes it the correct answer.

Correct Answer: D

Rationale: The correct answer is D: S phase. During the S phase of the cell cycle, DNA replication takes place to ensure each daughter cell receives a complete set of genetic material. This phase is characterized by the synthesis of new DNA strands. In contrast, choices A, B, and C (G phase, Prophase, Metaphase) are not associated with DNA replication. The G phase is a period of cell growth, Prophase is the initial stage of mitosis, and Metaphase is when chromosomes align. Therefore, the S phase is the specific stage where DNA replication occurs, making it the correct answer.