openstax microbiology test bank

Correct Answer: B

Rationale: The correct answer is B: Plasmids. Plasmids are extrachromosomal DNA molecules found in bacteria that can replicate independently of the bacterial chromosome. They carry additional genetic information, such as antibiotic resistance genes or virulence factors. Mesosomes (choice A) are not involved in carrying genetic information; they are infoldings of the cell membrane. Ribosomes (choice C) are cellular organelles responsible for protein synthesis, not carriers of genetic information. Choice D is incorrect as plasmids are indeed extrachromosomal carriers of genetic information in bacteria.

Correct Answer: A

Rationale: Rationale: 1. Gram-positive cocci in pairs indicate Streptococcus pneumoniae. 2. Presence of a capsule points to S. pneumoniae as it has a polysaccharide capsule. 3. S. pneumoniae commonly causes sore throat. 4. Neisseria meningitidis, Haemophilus influenzae, and Klebsiella pneumoniae are not typically associated with sore throat.

Correct Answer: B

Rationale: The correct answer is B: Ethambutol. Ethambutol is known to cause optic neuritis, affecting the visual nerve. It is a well-documented side effect of this drug. Isoniazid (Choice A) is associated with peripheral neuropathy, not optic neuritis. Kanamycin (Choice C) is known for its side effects on the inner ear, causing hearing loss. Rifampicin (Choice D) is not typically associated with optic neuritis but can cause other adverse effects like hepatitis. By process of elimination and knowledge of drug side effects, Ethambutol is the most likely culprit.

Correct Answer: A

Rationale: The correct answer is A: Treponema. Treponema pallidum is a spirochete bacterium that appears as long, thin, and spiral-shaped microorganisms with 8-12 regular coils under the microscope. This characteristic morphology is specific to Treponema species, making it the correct choice. Borrelia, Leptospira, and Vibrios have different shapes and arrangements under the microscope, making them incorrect choices in this scenario.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Gram-positive cocci in clusters suggest Staphylococcus or Streptococcus. 2. Catalase-positive and coagulase-positive narrow it down to Staphylococcus. 3. Staphylococcus aureus is catalase-positive and coagulase-positive. Therefore, the likely causative agent is Staphylococcus aureus. Summary: A: Correct - Staphylococcus aureus fits all the characteristics. B: Incorrect - Staphylococcus epidermidis is catalase-negative and coagulase-negative. C: Incorrect - Streptococcus pyogenes is catalase-negative and coagulase-negative. D: Incorrect - Enterococcus faecalis is catalase-negative and coagulase-negative.