mcgraw hill microbiology test bank

Correct Answer: C

Rationale: The correct answer is C: beaded. In an agar slant, beaded colonies appear as separate or semiconfluent, forming small, round colonies with gaps between them. This term accurately describes the appearance of the colonies in this context. A: Filiform colonies are dense and opaque with smooth edges, not separate or semiconfluent. B: Echinulate colonies have spiny projections, not the characteristic of separate or semiconfluent growth. D: Effuse colonies spread out extensively and lack defined borders, unlike the distinct appearance of separate or semiconfluent colonies.

Correct Answer: B

Rationale: The correct answer is B: Clostridium perfringens. This bacterium is associated with myonecrosis/gas gangrene and can produce enterotoxin causing food intoxication. Clostridium septicum (A) is associated with wound infections but not known for food intoxications. Clostridium histolyticum (C) is not typically associated with myonecrosis or food intoxications. Clostridium novyi (D) is known for causing black disease in sheep and cattle, not food intoxications.

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 correct answer is A: HSV-1. Herpes simplex infections on lips and in the mouth are most commonly caused by HSV-1 due to its preference for infecting oral mucosa. HSV-2 typically causes genital herpes. HSV-6 and HSV-7 are less common and not typically associated with oral infections. Therefore, based on the typical presentation and epidemiology of herpes simplex infections, HSV-1 is the most likely cause in this scenario.

Correct Answer: C

Rationale: The correct answer is C: Obligate anaerobes. These bacteria cannot survive in the presence of oxygen as they lack the necessary enzymes to detoxify reactive oxygen species. Obligate aerobes (A) require oxygen, facultative anaerobes (B) can grow with or without oxygen, and aerotolerant anaerobes (D) can survive in the presence of oxygen but do not utilize it for growth.