microbiology an evolving science test bank

Correct Answer: A

Rationale: The correct answer is A: Pertussis toxoid. This is because pertussis toxoid is a component of the pertussis vaccine, which provides specific prophylaxis against pertussis by stimulating the immune system to produce antibodies against the bacteria causing the disease. Choice B, killed vaccine, is incorrect as it does not specify pertussis toxoid. Choice C, wide-spectrum antibiotics, is incorrect as antibiotics are used for treatment, not prophylaxis. Choice D, None of the above, is incorrect as pertussis toxoid is specifically used for prophylaxis of pertussis.

Correct Answer: D

Rationale: The correct answer is D: TCBS. Thiosulfate-citrate-bile salts-sucrose (TCBS) agar is the most selective for Vibrio cholerae due to its high salt content, bile salts, and sucrose. Vibrio cholerae can grow well in alkaline conditions, which are provided by TCBS agar. MacConkey's agar (A) is selective for gram-negative bacteria, but not specifically for Vibrio cholerae. Chocolate agar (B) is a non-selective medium suitable for fastidious organisms. SS agar (C) is selective for Salmonella and Shigella species, not Vibrio cholerae.

Correct Answer: A

Rationale: The correct answer is A: Gram-negative stain. Pseudomonas aeruginosa is a gram-negative bacterium, as indicated by the bluish-green pus color. This bacterium has an outer membrane that retains the crystal violet stain, making it appear pink/red after the counterstain with safranin in Gram staining. The other choices are incorrect because Pseudomonas aeruginosa does not typically form spores (B), has a rod-shaped morphology rather than a coccal form (C), and does not exhibit cell pairing (D).

Correct Answer: B

Rationale: The correct answer is B: Penicillin. Penicillin is the drug of first choice for treating syphilis due to its effectiveness in eradicating the bacterium Treponema pallidum, which causes syphilis. It is the most reliable treatment with well-established efficacy. Gentamicin (A), ciprofloxacin (C), and chloramphenicol (D) are not recommended for treating syphilis as they are not effective against the specific bacteria causing the infection. Penicillin remains the gold standard for syphilis treatment.

Correct Answer: A

Rationale: Rationale: 1. Chagas disease is caused by Trypanosoma cruzi. 2. Trypanosoma cruzi is transmitted by triatomine bugs. 3. On a blood smear stained with Romanovsky's method, Trypanosoma cruzi appears as trypomastigotes. 4. Toxoplasma gondii causes toxoplasmosis, not Chagas disease. 5. Leishmania donovani and Leishmania tropica cause different forms of leishmaniasis, not Chagas disease.