microbiology an introduction test bank

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. The presence of Gram-positive cocci in pairs with a capsule is characteristic of Streptococcus pneumoniae. Step 1: Gram-positive cocci in pairs indicate a Streptococcus species. Step 2: The presence of a capsule suggests S. pneumoniae specifically. Summary: B: Staphylococcus aureus is a Gram-positive cocci but does not typically present in pairs with a capsule. C: Neisseria gonorrhoeae is a Gram-negative diplococcus, not a Gram-positive cocci. D: Klebsiella pneumoniae is a Gram-negative rod, not a cocci.

Correct Answer: A

Rationale: The correct answer is A because the secondary immune response is quicker due to memory B and T cells being already present from the primary response. These memory cells can quickly recognize and respond to the antigen upon re-exposure, leading to a faster and more efficient immune response. Choices B and C are incorrect as the secondary response produces more antibodies and requires fewer antigen stimulations. Choice D is also incorrect as the secondary response is faster than the primary response.

Correct Answer: A

Rationale: Exotoxins are proteins produced inside the microbe cell and then released outside the cell to exert their toxic effects on neighboring cells or tissues. This is why choice A is correct. Choices B and C are incorrect because exotoxins are not meant to act within the same cell they are produced in. Choice D is incorrect because exotoxins are usually released without causing cell lysis; they are secreted by the microbe actively rather than being leaked out due to cell damage.

Correct Answer: B

Rationale: The correct answer is B because Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis are the most common causative agents of bacterial meningitis. Haemophilus influenzae is often seen in children, Streptococcus pneumoniae is the most common in adults, and Neisseria meningitidis is common in adolescents and young adults. Choice A is incorrect because although Streptococcus group B and Listeria monocytogenes can cause meningitis, E. Coli K1 is not a common causative agent. Choice C is incorrect because Staphylococcus aureus and Pseudomonas aeruginosa are not typically associated with bacterial meningitis. Choice D is incorrect as there are known causative agents for bacterial meningitis.

Correct Answer: A

Rationale: Rationale for correct answer (A: Escherichia coli): 1. Endo agar selects for Gram-negative bacteria. 2. Red colonies on Endo agar indicate lactose fermentation, characteristic of E. coli. 3. E. coli is a common cause of pneumonia, especially in immunocompromised patients. Summary of why other choices are incorrect: - B: Klebsiella pneumoniae: Typically forms mucoid colonies on agar. - C: Pseudomonas aeruginosa: Produces characteristic greenish-blue colonies on agar. - D: Proteus mirabilis: Does not typically ferment lactose, so would not produce red colonies on Endo agar.