microbiology an introduction test bank

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A patient with severe abdominal pain had a stool culture revealing non-lactose-fermenting, Gram-negative rods that produce gas in nutrient broth. What is the most likely causative agent?

  • A. Salmonella enterica
  • B. Shigella dysenteriae
  • C. Escherichia coli
  • D. Proteus vulgaris
Correct Answer: D

Rationale: The correct answer is D: Proteus vulgaris. This is because Proteus species are non-lactose-fermenting, Gram-negative rods that produce gas in nutrient broth. They are known to cause severe abdominal pain due to their ability to invade the intestinal mucosa.

A: Salmonella enterica is a lactose-fermenting organism and typically does not produce gas in nutrient broth.
B: Shigella dysenteriae is a lactose-negative organism but does not produce gas in nutrient broth.
C: Escherichia coli is a lactose-fermenting organism and does not typically produce gas in nutrient broth.

In summary, the presence of non-lactose-fermenting, gas-producing Gram-negative rods points towards Proteus vulgaris as the most likely causative agent of the severe abdominal pain.

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A 19 year old woman suffers from primary syphilis. Doctor administered her complex therapy that includes benzylpenicillin sodium salt. What is the mechanism of action of this drug?

  • A. It blocks synthesis of peptidoglycan of microbial membrane
  • B. It blocks synthesis of cytoplasm proteins
  • C. It blocks thiol enzymes
  • D. It blocks RNA synthesis
Correct Answer: A

Rationale: The correct answer is A. Benzylpenicillin sodium salt, also known as penicillin G, works by blocking the synthesis of peptidoglycan in the microbial cell wall. Peptidoglycan is crucial for the structural integrity of bacterial cell walls. By inhibiting its synthesis, penicillin disrupts the cell wall formation, leading to cell lysis and bacterial death. Choices B, C, and D are incorrect because penicillin does not target cytoplasm proteins, thiol enzymes, or RNA synthesis. Penicillin's primary mode of action is specifically related to interfering with bacterial cell wall synthesis.

The sample used to proving epidemic meningitis is:

  • A. CSF transported at 37°C (CSF sample, blood, nasopharyngeal secretion)
  • B. Feces
  • C. CSF transported at +4°C
  • D. None of the above
Correct Answer: A

Rationale: The correct answer is A because CSF (Cerebrospinal fluid) is the sample used for proving epidemic meningitis. It should be transported at 37°C to maintain its integrity. Blood and nasopharyngeal secretions are not typically used for diagnosing meningitis. Choice B, feces, is unrelated to the diagnosis of meningitis. Choice C, CSF transported at +4°C, is incorrect as it should be transported at 37°C to prevent degradation of the sample. Therefore, A is the correct choice for proving epidemic meningitis due to the specificity of the sample and the proper transport conditions.

Gram staining is used to differentiate bacteria based on:

  • A. size and shape
  • B. presence of flagella
  • C. cell wall composition
  • D. genetic material
Correct Answer: C

Rationale: The correct answer is C: cell wall composition. Gram staining differentiates bacteria based on the structure of their cell walls. It classifies bacteria into Gram-positive (thick peptidoglycan layer) and Gram-negative (thin peptidoglycan layer). This differentiation is crucial for identifying bacterial species and guiding treatment choices. Size and shape (choice A) are not specific to Gram staining. Presence of flagella (choice B) is related to bacterial motility, not Gram staining. Genetic material (choice D) is not directly assessed by Gram staining. Overall, the unique composition of the cell wall is the key factor in distinguishing bacteria through Gram staining.

Which is not true?

  • A. Interferon beta is produced by the fibroblasts
  • B. Interferon alpha is produced by the leukocytes
  • C. Interferon gamma is produced by the lymphocytes
  • D. Interferon delta is produced by the macrophages
Correct Answer: D

Rationale: Interferon delta is not a known type of interferon, making choice D incorrect. Interferon beta is indeed produced by fibroblasts (choice A), interferon alpha by leukocytes (choice B), and interferon gamma by lymphocytes (choice C). Each type of interferon is produced by specific cells in the immune system, contributing to the body's defense against viruses and other pathogens.

A patient has symptoms of inflammation of urogenital tracts. Examination of a vaginal smear revealed big monocellular, pear-shaped organisms with the pointed spike at the posterior end of body, big nucleus and undulating membrane. What protozoa were found in the smear?

  • A. Trichomonas vaginalis
  • B. Trichomonas hominis
  • C. Trichomonas buccalis
  • D. Trypanosoma gambiense
Correct Answer: A

Rationale: Rationale: The correct answer is A: Trichomonas vaginalis.
1. Symptoms of urogenital inflammation match Trichomonas vaginalis infection.
2. Description matches Trichomonas vaginalis characteristics: pear-shaped, pointed spike, big nucleus, undulating membrane.
3. Trichomonas hominis and buccalis do not typically infect urogenital tracts.
4. Trypanosoma gambiense causes African trypanosomiasis, not urogenital infections.

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