mcgraw hill microbiology test bank

Correct Answer: B

Rationale: The correct answer is B: IgM. IgM antibodies are the first type of antibodies produced in response to an infection, indicating an active or recent infection. In the case of a rubella virus infection in a fetus, IgM antibodies can be detected in the umbilical cord blood, confirming the presence of the virus. IgA antibodies are mainly found in mucosal areas, IgG antibodies indicate past infection or immunity, and IgD antibodies play a role in B cell activation but are not typically detected in this context.

Correct Answer: B

Rationale: The correct answer is B: Sexual transmission. The symptoms described are indicative of a vaginal yeast infection caused by Candida albicans. The presence of large gram-positive oval oblong cells forming pseudomycelium is characteristic of Candida infection. Sexual transmission is the most probable channel of infection as Candida can be transmitted through sexual contact. Endogenous infection (A) refers to infections originating from the body's own flora, which is not the case here. Contact infection (C) typically involves direct physical contact or fomite transmission, which is less likely in this scenario. Vector-borne transmission (D) involves transmission through vectors like mosquitoes or ticks, which is not relevant in this case.

Correct Answer: A

Rationale: The presence of acid-fast bacilli stained red against a blue background indicates mycobacteria, specifically Mycobacterium tuberculosis in this case. Ziehl-Neelsen staining is commonly used to detect tuberculosis. Diphtheria is caused by Corynebacterium diphtheriae, which does not stain with Ziehl-Neelsen. Pneumonia is a general term for lung infections caused by various pathogens. Leprosy is caused by Mycobacterium leprae, which requires special staining methods different from Ziehl-Neelsen.

Correct Answer: B

Rationale: The correct answer is B: Gram negative coccobacillus. Bordetella pertussis, the causative agent of pertussis, is a gram-negative coccobacillus. This is because it is a small, rod-shaped bacterium that appears both as a bacillus (rod-shaped) and a coccus (spherical) shape. It does not retain the crystal violet stain in the Gram staining process, indicating its negative gram nature. Choice A is incorrect because pertussis is not a gram-positive bacillus. Choice C is incorrect because pertussis is not a long gram-negative rod-shaped bacterium. Choice D is incorrect as the other options do not accurately describe the morphology of Bordetella pertussis.

Correct Answer: B

Rationale: The correct answer is B: Vibrio cholerae. Cholera is caused by Vibrio cholerae, a gram-negative bacterium that produces a toxin leading to severe watery diarrhea. Shigella dysenteriae causes dysentery, not cholera. Salmonella enterica causes salmonellosis, not cholera. Clostridium perfringens is associated with food poisoning, not cholera. In summary, Vibrio cholerae is the correct answer because it is the specific bacterium known to cause cholera, while the other choices are associated with different diseases.