mcgraw hill microbiology test bank

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By what mechanism does MRSA achieve resistance to standard beta-lactam antibiotics?

  • A. Extended spectrum beta-lactamases
  • B. Penicillin efflux pump
  • C. Altered peptide sequence in peptidoglycan
  • D. Altered penicillin binding proteins
Correct Answer: D

Rationale: The correct answer is D: Altered penicillin binding proteins. MRSA (Methicillin-resistant Staphylococcus aureus) achieves resistance to beta-lactam antibiotics, such as penicillin, by producing altered penicillin binding proteins that have reduced affinity for these antibiotics. This alteration prevents the antibiotics from binding to their target sites on the bacterial cell wall, thus rendering them ineffective.

Choice A, extended spectrum beta-lactamases, are enzymes produced by some bacteria to break down beta-lactam antibiotics, but MRSA does not use this mechanism. Choice B, penicillin efflux pump, is a mechanism where bacteria pump out antibiotics from their cells, but this is not how MRSA develops resistance. Choice C, altered peptide sequence in peptidoglycan, does not directly relate to how MRSA resists beta-lactam antibiotics.

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Which of the following best describes the role of bacterial plasmids?

  • A. Regulation of bacterial growth
  • B. Carrying antibiotic resistance genes
  • C. Producing toxins
  • D. Facilitating endospore formation
Correct Answer: B

Rationale: The correct answer is B: Carrying antibiotic resistance genes. Bacterial plasmids are small, circular DNA molecules that can carry genes, including those for antibiotic resistance. This allows bacteria to survive exposure to antibiotics. Plasmids do not directly regulate bacterial growth (A), produce toxins (C), or facilitate endospore formation (D). Plasmids play a crucial role in the spread of antibiotic resistance among bacteria.

The term “infectious process†means “all biological processes carried out after…â€

  • A. The attachment and penetration of microbes into the microorganism
  • B. The attachment and penetration of microbes into the microorganisms regardless of whether or not there is clinical manifestation
  • C. The penetration of microbes into the macroorganism and always manifest clinically
  • D. No correct answer
Correct Answer: B

Rationale: The correct answer is B because the term "infectious process" refers to all biological processes that occur after the attachment and penetration of microbes into the host organism, regardless of whether there are clinical manifestations. This includes the colonization, multiplication, and spread of the microorganisms within the host.

Explanation:
A: Incorrect because it only mentions the attachment and penetration of microbes into the microorganism, missing the subsequent processes.
C: Incorrect because it is too specific, stating that the penetration of microbes always manifests clinically, which is not always the case.
D: Incorrect because there is a correct answer, which is B, as explained above.

Microscopy of sputum revealed acid-fast bacilli stained red against a blue background using Ziehl-Neelsen staining. What disease does this finding suggest?

  • A. Tuberculosis
  • B. Diphtheria
  • C. Pneumonia
  • D. Leprosy
Correct Answer: A

Rationale: The presence of acid-fast bacilli stained red against a blue background indicates mycobacteria, specifically Mycobacterium tuberculosis in this case. Ziehl-Neelsen staining is commonly used to detect tuberculosis. Diphtheria is caused by Corynebacterium diphtheriae, which does not stain with Ziehl-Neelsen. Pneumonia is a general term for lung infections caused by various pathogens. Leprosy is caused by Mycobacterium leprae, which requires special staining methods different from Ziehl-Neelsen.

Which bacteria are known for causing urinary tract infections?

  • A. Escherichia coli
  • B. Salmonella enterica
  • C. Neisseria gonorrhoeae
  • D. All of the above
Correct Answer: D

Rationale: The correct answer is D, "All of the above." Escherichia coli is the most common bacteria causing UTIs due to its ability to colonize the urinary tract. Salmonella enterica and Neisseria gonorrhoeae are not typically associated with UTIs. Therefore, by process of elimination, since A is correct, B and C are incorrect.

An outbreak of food poisoning was recorded in an urban settlement. The illness was diagnosed as botulism on the grounds of clinical presentations. What foodstuffs should be chosen for analysis in the first place in order to confirm the diagnosis?

  • A. Tinned food
  • B. Potatoes
  • C. Pasteurized milk
  • D. Boiled meat
Correct Answer: A

Rationale: The correct answer is A: Tinned food. Botulism is often caused by the botulinum toxin produced by the bacterium Clostridium botulinum, which can be present in improperly canned foods. Analyzing tinned food allows for direct detection of the toxin or bacteria, confirming the diagnosis. Potatoes, pasteurized milk, and boiled meat are less likely sources of botulism compared to tinned food, making them less suitable for initial analysis in this case.

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