Correct Answer: B

Rationale: The correct answer is B: Shagreen leather. Yersinia pestis, the bacterium causing plague, forms colonies resembling shagreen leather on a hard nutrient medium due to its distinctive morphology. This morphology includes a rough, irregular, and raised appearance, similar to the texture of shagreen leather. A: Dewdrops - Incorrect. Dewdrops do not accurately describe the colony morphology of Yersinia pestis. C: Lace handkerchief - Incorrect. Lace handkerchief does not accurately describe the colony morphology of Yersinia pestis. D: Mercury drops - Incorrect. Mercury drops do not accurately describe the colony morphology of Yersinia pestis.

Correct Answer: A

Rationale: Step-by-step rationale for why the correct answer is A (Cholera): 1. Gram-negative curved mobile monotrichous bacilli: Vibrio cholerae, the causative agent of cholera, fits this description. 2. Do not produce spores or capsules: Vibrio cholerae does not produce spores or capsules. 3. Require alkaline reaction (pH 8.5-9.5): Vibrio cholerae thrives in alkaline environments. 4. Enteric infection: Cholera is a classic example of an enteric infection transmitted through contaminated food or water. Summary of why other choices are incorrect: B: Shigellosis is caused by Shigella species, which are gram-negative, but they are not curved bacilli and do not require an alkaline pH. C: Typhoid fever is caused by Salmonella Typhi, which are gram-negative but are not curved bacilli and do not require an alkaline pH.

Correct Answer: A

Rationale: 1. Gram-positive cocci in clusters suggest Staphylococcus species. 2. Catalase-positive and coagulase-positive characteristics match with Staphylococcus aureus. 3. Staphylococcus aureus is a common cause of wound infections due to its virulence factors. 4. Other choices are incorrect: B) S. epidermidis is coagulase-negative and a common contaminant, C) S. pyogenes is catalase-negative, D) Enterococcus faecalis is not typically associated with wound infections.

Correct Answer: A

Rationale: Step 1: Ziehl-Neelsen staining is a type of acid-fast staining used to detect acid-resistant bacteria like Mycobacterium species. Step 2: Acid-resistant bacteria have a high lipid content in their cell walls, making them resist decolorization with acid-alcohol. Step 3: Mycobacterium species, such as M. tuberculosis and M. leprae, are examples of acid-resistant bacteria. Step 4: Spores are not typically stained using Ziehl-Neelsen staining, making choice B incorrect. Step 5: Metachromatic bodies are stained using specific techniques like Albert's stain, not Ziehl-Neelsen staining, making choice C incorrect. Summary: Ziehl-Neelsen staining is specifically used for acid-resistant bacteria detection, making choice A the correct answer. Choices B and C are incorrect as they do not align with the purpose of Ziehl-Neelsen staining. Choice D is incorrect as Ziehl

Correct Answer: A

Rationale: The correct answer is A: Tuberculine. The Mantoux test involves injecting tuberculin, a protein derivative of Mycobacterium tuberculosis, under the skin. This test helps determine if a person has been exposed to the bacteria that cause TB. Administering tuberculin is crucial for the Mantoux test as it triggers a delayed-type hypersensitivity reaction in individuals previously exposed to TB. Choice B (BCG vaccine) is incorrect because BCG does not interfere with the Mantoux test results. Choice C (DPT vaccine) is incorrect as it is used for immunization against diphtheria, pertussis, and tetanus, not for diagnosing TB. Choice D (Tularin test) is incorrect as it is not a recognized immunobiological agent for TB diagnosis.