A child entering the school for the first time was given Mantoux test in order to determine if there was a need for revaccination. The reaction was negative. What is the meaning of this test result?

Correct Answer: B

Rationale: The correct answer is B: Availability of cell-mediated immunity to tuberculosis. A negative Mantoux test indicates the presence of an immune response to the TB bacteria, as the test measures the body's delayed hypersensitivity reaction to TB antigens. This means the child has been exposed to TB in the past or has been vaccinated, resulting in the development of cell-mediated immunity against TB. Incorrect choices: A: No cell-mediated immunity to tuberculosis - This is incorrect as a negative Mantoux test actually indicates the presence of cell-mediated immunity. C: No antibodies to the tuberculosis bacteria - Mantoux test measures cell-mediated immunity, not antibody response. D: No anti-toxic immunity to tuberculosis - Mantoux test does not assess anti-toxic immunity, it specifically measures cell-mediated immunity.

Correct Answer: A

Rationale: Rationale: 1. Metronidazole is known to inhibit aldehyde dehydrogenase, an enzyme involved in alcohol metabolism. 2. Inhibition of this enzyme leads to accumulation of acetaldehyde, causing unpleasant symptoms when alcohol is consumed. 3. This reaction is known as the disulfiram-like reaction. 4. Reserpine, Clonidine, and Diazepam do not have this specific mechanism of action. Summary: - Option A (Metronidazole) is correct due to its inhibition of alcohol metabolism. - Options B, C, and D are incorrect as they do not exhibit this interaction with alcohol metabolism.

Correct Answer: A

Rationale: Step 1: Initial diagnosis of influenza suggests a viral illness. Step 2: Presence of maculopapular petechial rash and high fever indicates a systemic infection. Step 3: Symptoms like euphoria, hyperemia, tachycardia, splenomegaly, and excitement are characteristic of epidemic typhus. Step 4: Face hyperemia, sclera reddening, and tongue tremor are specific to epidemic typhus. Step 5: Epidemic typhus is transmitted by body lice, which fits the scenario of a patient without permanent residence. Summary: - Delirium alcoholicum is unlikely due to the specific symptoms and lack of history of alcohol abuse. - Leptospirosis typically presents with jaundice and renal symptoms, not seen in this case. - Measles rash is different from the maculopapular petechial rash described.

Correct Answer: D

Rationale: The correct answer is D (All of the above) because all three bacteria mentioned (Clostridium botulinum, Salmonella enterica, Escherichia coli) are associated with foodborne illnesses. Clostridium botulinum causes botulism, Salmonella enterica causes salmonellosis, and Escherichia coli can cause food poisoning. Each of these bacteria can contaminate food and lead to illnesses when consumed. Therefore, selecting all of the above is the correct choice. The other choices (A, B, C) are incorrect because each of those bacteria individually is associated with foodborne illnesses.

Correct Answer: C

Rationale: The correct answer is C: acetyl-CoA. Acetyl-CoA is the compound that combines with oxaloacetic acid at the beginning of the Krebs cycle to form citric acid. This step is essential for the cycle to proceed, making acetyl-CoA the correct choice. A: Citric acid is formed after acetyl-CoA combines with oxaloacetic acid, so it is a product of the reaction, not the compound that enters the cycle. B: Pyruvic acid is converted to acetyl-CoA in a separate process before entering the Krebs cycle. D: Phosphoglyceraldehyde is not involved in the Krebs cycle; it is a compound in glycolysis.

Correct Answer: C

Rationale: The correct answer is C: circular double-stranded DNA. Bacterial genomes are typically composed of circular double-stranded DNA due to its stability and efficient replication. Circular DNA allows for continuous replication without the need for telomeres present in linear DNA (choice B). Bacteria do not typically have double-stranded RNA genomes (choice A) as RNA is more commonly found in viruses. Single-stranded DNA (choice D) is not typically the main genetic material in bacteria, as it is less stable and less efficient for information storage compared to double-stranded DNA.

Correct Answer: A

Rationale: The correct answer is A: Vibrio cholerae. This is because Vibrio cholerae is a Gram-negative, comma-shaped bacterium known to cause cholera. The characteristic shape and the association with cholera make it the most likely causative agent in this case. Explanation for incorrect choices: B: Shigella dysenteriae - Shigella dysenteriae is a Gram-negative bacterium that causes bacillary dysentery, not cholera. C: Salmonella typhi - Salmonella typhi is a Gram-negative bacterium that causes typhoid fever, not cholera. D: Campylobacter jejuni - Campylobacter jejuni is a Gram-negative bacterium that commonly causes foodborne gastroenteritis, not cholera.

Correct Answer: A

Rationale: The correct answer is A: Neisser's staining. Neisser's staining is used to detect metachromatic granules in bacteria, which appear as dark blue-staining granules at the ends of rod-shaped bacteria in diphtheria. This technique specifically targets these granules, making it ideal for identifying Corynebacterium diphtheriae, the causative agent of diphtheria. Ziehl-Neelsen staining is used for acid-fast bacteria like Mycobacterium tuberculosis, Gram staining is for classifying bacteria based on cell wall composition, and Giemsa staining is used for detecting parasites and certain blood cells, making them incorrect for identifying granules in diphtheria.

Correct Answer: B

Rationale: The correct answer is B because the complement fixation test is a serological test that detects the presence of specific antibodies or antigens in a patient's serum. It works by measuring the ability of antibodies to fix complement proteins. Choice A is incorrect because the complement fixation test typically involves several steps, not necessarily three. Choice C is incorrect as standardized complement proteins are commonly used in this test. Choice D is incorrect because sheep red blood cells are not essential for performing the complement fixation test.