microbiology basic and clinical principles test bank

Correct Answer: B

Rationale: The correct answer is B: 3.5 to 4.0 billion years. This range aligns with the oldest known fossils of prokaryotes found in ancient rocks. Fossils dating back to this time period provide evidence of early life forms on Earth. Choices A, C, and D are incorrect because they fall outside the established timeline based on scientific evidence and fossil records. A (4.0 to 5.0 billion years) is too early for the oldest prokaryote fossils, as it predates the formation of Earth's atmosphere suitable for life. C (2.5 to 3.0 billion years) and D (2.2 to 2.7 billion years) are too recent for the oldest prokaryote fossils, as life is believed to have originated much earlier.

Correct Answer: B

Rationale: The correct answer is B: Yersinia pestis. Yersinia pestis is the bacterium responsible for causing the plague, specifically the bubonic plague. It is transmitted through fleas and rodents. Escherichia coli (A) is a common gut bacterium, Clostridium difficile (C) causes antibiotic-associated diarrhea, and Staphylococcus aureus (D) is associated with skin infections, but they are not responsible for causing the plague.

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. Step 1: Gram-negative diplococci - characteristic of Neisseria species. Step 2: Oxidase-positive - Neisseria species are oxidase-positive. Step 3: Fermentative - Neisseria meningitidis is a fermentative bacterium. Therefore, Neisseria meningitidis is the most likely causative agent. Summary: - B: Neisseria gonorrhoeae is also a Neisseria species but is not fermentative. - C: Moraxella catarrhalis is oxidase-positive but not fermentative. - D: Haemophilus influenzae is not a Neisseria species and is not typically fermentative.

Correct Answer: A

Rationale: The correct answer is A: Clostridium tetani. This bacterium is known for causing tetanus due to its ability to produce tetanospasmin, a neurotoxin that leads to the characteristic muscle stiffness and spasms seen in tetanus. Clostridium perfringens (Choice B) is associated with gas gangrene, Streptococcus pyogenes (Choice C) causes streptococcal infections, and Escherichia coli (Choice D) is known for causing various gastrointestinal infections. Therefore, Choices B, C, and D are incorrect as they are not the causative agents of tetanus.

Correct Answer: C

Rationale: Correct Answer: C: Halophiles Rationale: 1. Halophiles are bacteria adapted to high salt environments. 2. They have specific mechanisms to tolerate high salt concentrations. 3. Acidophiles thrive in acidic conditions. 4. Thermophiles prefer high temperature environments. 5. Mesophiles grow best at moderate temperatures.