Microbiology An Evolving Science Test Bank

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. Anaerobic bacteria are sensitive to metronidazole due to its mechanism of action targeting their DNA. Metronidazole is often the drug of choice for treating infections caused by anaerobic bacteria. Gentamicin, Oxacillin, and Co-trimoxazole are not effective against anaerobes. Gentamicin is an aminoglycoside mostly used for aerobic bacteria, Oxacillin is a beta-lactam antibiotic effective against gram-positive bacteria, and Co-trimoxazole is a combination of sulfamethoxazole and trimethoprim mainly used for urinary tract infections and some respiratory infections.

Correct Answer: A

Rationale: The correct answer is A because Klebsiella species have a real capsule, which is a distinguishing feature used for their identification. This capsule helps them evade the host immune response. Additionally, Klebsiella species are non-motile, meaning they do not possess flagella for movement. Choices B and C are incorrect because Klebsiella species are facultative anaerobes and do not form spores under any conditions. Choice D is also incorrect as option A is the correct statement for genus Klebsiella.

Correct Answer: C

Rationale: The correct answer is C (7.2-7.4) because most pathogenic bacteria and viruses thrive in a neutral pH environment close to 7.0. This pH range is optimal for their growth and survival. Choice A (5.0-5.5) is too acidic for most pathogens. Choice B (8.0-9.6) is too alkaline, which is not conducive for their survival. Choice D (4.2-4.4) is also too acidic and would likely inhibit the growth of pathogenic bacteria and viruses. Thus, a pH range of 7.2-7.4 provides the most suitable conditions for their proliferation.

Correct Answer: A

Rationale: The correct answer is A: Bordetella pertussis. This bacterium causes whooping cough by attaching to the respiratory tract and releasing toxins that lead to severe coughing fits. Clostridium tetani causes tetanus, not whooping cough. Haemophilus influenzae can cause respiratory infections but not specifically whooping cough. Staphylococcus aureus is known for causing skin infections and not respiratory diseases like whooping cough. Therefore, the presence of Bordetella pertussis and its specific mechanism of causing whooping cough makes it the correct answer.

Correct Answer: A

Rationale: Rationale: Shigella dysenteriae produces Shiga toxin, which inhibits protein synthesis by inactivating the 60S ribosomal subunit. This disrupts the translation process, leading to cell death. Escherichia coli (choice B) does not produce a toxin that inhibits protein synthesis. Clostridium tetani (choice C) produces tetanospasmin, which affects the nervous system. Staphylococcus aureus (choice D) produces toxins that cause food poisoning but do not inhibit protein synthesis.