medical microbiology test bank

Correct Answer: C

Rationale: The correct answer is C: Endospore. Endospores are highly resistant structures formed by certain bacterial species to withstand harsh conditions like desiccation. They contain a tough outer layer that protects the bacterial DNA and other essential components. Capsules (choice A) provide protection against host immune responses but not specifically against desiccation. Flagella (choice B) are used for bacterial motility. Pili (choice D) are involved in bacterial adhesion but do not protect against desiccation. Therefore, endospores are the most suitable choice for protecting against desiccation.

Correct Answer: D

Rationale: The correct answer is D because all three bacteria listed can produce toxins that cause severe diarrhea. Clostridium difficile produces toxins that can lead to antibiotic-associated diarrhea, Vibrio cholerae produces a toxin that causes cholera, and certain strains of Escherichia coli produce toxins that result in severe diarrhea. Therefore, choosing option D is correct because all the mentioned bacteria can cause severe diarrhea. Options A, B, and C are incorrect individually because each bacterium listed can produce a toxin resulting in severe diarrhea.

Correct Answer: B

Rationale: The correct answer is B: Sporadic disease. When an infection occurs in several persons without any epidemiological link, it is considered sporadic. This term is used to describe isolated cases that do not form a specific pattern or cluster. It indicates random occurrences and lack of connection between the affected individuals. A: Epidemic refers to a sudden increase in the number of cases of a disease within a specific population or region, usually linked by a common source or exposure. C: Endemic signifies the constant presence of a disease within a specific population or region, with cases occurring at a relatively stable rate. D: Pandemic indicates a global outbreak of a disease affecting a large number of people across multiple countries or continents.

Correct Answer: C

Rationale: The correct answer is C: Bacillus subtilis. Bacillus subtilis is known for its spore-forming ability, which is a survival mechanism to withstand harsh conditions. Spore formation allows the bacteria to become dormant and resistant to heat, chemicals, and radiation. Escherichia coli (A) is not known for spore formation. Staphylococcus aureus (B) does not form spores either. Listeria monocytogenes (D) is a pathogenic bacterium but does not typically form spores.

Correct Answer: B

Rationale: The correct answer is B: Spirochete. Lyme disease is caused by the bacterium Borrelia burgdorferi, which is a spirochete. Spirochetes are spiral-shaped bacteria that move by rotating like a corkscrew, which is characteristic of Borrelia burgdorferi. A: Spirillum - Spirillum bacteria are helical-shaped but are not the causative agent for Lyme disease. C: Vibrio - Vibrio bacteria are curved or comma-shaped and are not associated with Lyme disease. D: Diplococcus - Diplococcus bacteria are spherical-shaped and typically occur in pairs, not the causative agent for Lyme disease. Therefore, the correct answer is B because Borrelia burgdorferi is a spirochete bacterium that causes Lyme disease.