Microbiology A Systems Approach Test Bank

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A 40 year old man noticed a reddening and an edema of skin in the area of his neck that later developed into a small abscess. The incised focus is dense, yellowish-green. The pus contains white granules. Histological examination revealed drusen of a fungus, plasmatic and xanthome cells, macrophages. What type of mycosis is the most probable?

  • A. Actinomycosis
  • B. Aspergillosis
  • C. Candidosis
  • D. Sporotrichosis
Correct Answer: D

Rationale: The correct answer is D: Sporotrichosis. Sporotrichosis is caused by the fungus Sporothrix schenckii, which commonly presents as a subcutaneous infection. In the given case, the presence of a small abscess with yellowish-green pus containing white granules is indicative of sporotrichosis. The histological examination showing drusen of a fungus, plasmatic and xanthome cells, and macrophages further supports the diagnosis of sporotrichosis.

Choice A: Actinomycosis is a bacterial infection caused by Actinomyces species, not a fungal infection.
Choice B: Aspergillosis is caused by Aspergillus species and typically presents as a pulmonary infection, not a subcutaneous abscess as described in the case.
Choice C: Candidosis is caused by Candida species and usually presents as mucocutaneous infections, not a subcutaneous abscess with the

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Microscopic analysis of a smear stained by Ziehl-Neelsen method revealed bright red bacilli. What microorganism is being tested for?

  • A. Mycobacterium tuberculosis
  • B. Staphylococcus aureus
  • C. Clostridium tetani
  • D. Escherichia coli
Correct Answer: A

Rationale: The Ziehl-Neelsen stain is specific for acid-fast bacteria like Mycobacterium tuberculosis. The bright red bacilli seen in the smear indicate the presence of acid-fast organisms, which is characteristic of Mycobacterium tuberculosis. Staphylococcus aureus, Clostridium tetani, and Escherichia coli are not acid-fast bacteria and would not be stained red using the Ziehl-Neelsen method. Therefore, the correct answer is A: Mycobacterium tuberculosis.

Which of the following food media can be used for cultivation of Streptococcus pneumoniae:

  • A. Blood agar
  • B. MacConkey agar
  • C. Peptone water
  • D. None of the above
Correct Answer: A

Rationale: The correct answer is A: Blood agar. Streptococcus pneumoniae is a fastidious bacterium that requires enriched media for growth. Blood agar provides the necessary nutrients and growth factors for the cultivation of S. pneumoniae, such as blood proteins and hemin. MacConkey agar (B) is selective for gram-negative bacteria and would not support the growth of S. pneumoniae. Peptone water (C) is a liquid medium that lacks the necessary nutrients for the growth of S. pneumoniae. Choice D is incorrect as blood agar is a suitable medium for cultivating S. pneumoniae.

During the staining of sputum smear of a patient with suspected croupous pneumonia the following reactives and stainers were used: gentian violet solution, Lugol's solution, 960 spiritus and water fuchsin. What method of staining is used in this case?

  • A. Leffler's
  • B. Gram's
  • C. Ziehl-Neelsen's
  • D. Neisser's
Correct Answer: B

Rationale: The correct answer is B: Gram's staining method. The rationale for this is as follows: Gentian violet and Lugol's solution are used as primary and mordant stains in the Gram's staining method. Spiritus 960 is used as a decolorizer, and water fuchsin is used as a counterstain. This staining method is commonly used in microbiology to differentiate bacteria into Gram-positive and Gram-negative based on their cell wall characteristics.

A: Leffler's staining method is used for the identification of diphtheria bacilli.
C: Ziehl-Neelsen's staining method is used for acid-fast bacteria like Mycobacterium tuberculosis.
D: Neisser's staining method is used for the identification of Neisseria species.

In summary, the use of specific reactives and stainers in the question indicates the application of the Gram's staining method for bacterial differentiation.

Two weeks after hemotransfusion a patient developed fever. What protozoal disease can be suspected?

  • A. Malaria
  • B. Toxoplasmosis
  • C. Leishmaniasis
  • D. Amebiasis
Correct Answer: A

Rationale: The correct answer is A: Malaria. Two weeks after hemotransfusion, the onset of fever indicates a possible bloodborne infection. Malaria is a protozoal disease transmitted through infected blood, causing symptoms like fever. Toxoplasmosis, Leishmaniasis, and Amebiasis are not typically associated with fever following hemotransfusion. Malaria fits the timeline and mode of transmission in this scenario.

The specific prevention (by vaccination) of the disease gas gangrene (caused by Clostridium perfringens) is based on:

  • A. Killed whole cell vaccine
  • B. Anatoxin
  • C. There is no specific prevention by vaccination
  • D. Alive attenuated vaccine
Correct Answer: B

Rationale: The correct answer is B: Anatoxin. An anatoxin is a toxin that has been rendered harmless while retaining its ability to stimulate an immune response. Gas gangrene is caused by the toxins produced by Clostridium perfringens, not the bacteria itself. Therefore, vaccination with an anatoxin can trigger the immune system to produce antibodies against the toxin, providing immunity against the disease.

A: Killed whole cell vaccine - Gas gangrene is caused by toxins, not the whole bacterium. This type of vaccine may not be effective in preventing the disease.
C: There is no specific prevention by vaccination - This is incorrect, as vaccination with an anatoxin can prevent gas gangrene.
D: Alive attenuated vaccine - Attenuated vaccines contain live, weakened forms of the pathogen. However, for gas gangrene prevention, targeting the specific toxin with an anatoxin vaccine is more appropriate.

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