microbiology basic and clinical principles test bank

Correct Answer: A

Rationale: The correct answer is A: Head lice. Epidemic typhus is transmitted by the body louse, Pediculus humanus humanus, which is different from the head louse, Pediculus humanus capitis. Head lice are not known to transmit epidemic typhus. Body lice are the primary vectors for transmitting epidemic typhus. Fleas are vectors for other diseases such as plague, not epidemic typhus. Ticks are vectors for various diseases but not for epidemic typhus. Therefore, the correct vector for epidemic typhus transmission is body lice, making choice A the correct answer.

Correct Answer: C

Rationale: The correct answer is Shigella (Choice C) because it matches the description of being Gram-negative rods and lactose non-fermenters. Shigella is a non-lactose fermenting, Gram-negative rod that typically produces colorless colonies on Endo agar. Salmonella (Choice A) and Escherichia coli (Choice B) are both lactose fermenters and would produce pink colonies on Endo agar. Proteus (Choice D) is also a lactose fermenter and would appear pink on Endo agar. Therefore, based on the characteristics provided, Shigella is the most likely microorganism in this scenario.

Correct Answer: A

Rationale: The correct answer is A: Mycolic acid in the cell wall. Mycolic acid is a unique component of the cell wall of Mycobacterium species, including the causative agent of tuberculosis. The Ziehl-Neelsen method uses acid-fast staining, where mycolic acid confers resistance to decolorization by acid-alcohol, causing the bacteria to retain the red stain. Choices B, C, and D are incorrect as capsules, flagella, and peptidoglycan layers do not directly contribute to acid-fast staining characteristic of Mycobacterium species.

Correct Answer: A

Rationale: The correct answer is A: Neisseria meningitidis. This is because Neisseria meningitidis is a Gram-negative diplococcus known to cause bacterial meningitis, presenting with fever, headache, and neck stiffness. It is a common cause of meningitis in young adults and teenagers. Streptococcus pneumoniae (B) is a Gram-positive bacteria and a common cause of bacterial pneumonia, not meningitis. Haemophilus influenzae (C) is a Gram-negative coccobacillus that can cause meningitis, but it is less common in adults. Klebsiella pneumoniae (D) is a Gram-negative bacillus known to cause pneumonia and urinary tract infections, not meningitis.

Correct Answer: B

Rationale: The capsule of Bacillus anthracis is made of polypeptide. This is because the capsule is composed of a protein-based material that surrounds the bacterium, providing protection and aiding in its virulence. Polysaccharides, lipids, and the absence of capsules are not characteristic of Bacillus anthracis' capsule structure, making choices A, C, and D incorrect, respectively.