microbiology a systems approach test bank

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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.

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A 49-year-old countryman got an itching papule on the dorsum of his right hand. In the centre there is a vesicle with serosanginous exudate. Within the next 2 days the patient developed a painless edema of hand and forearm. On the 4th day the temperature rose to 38,5oC, in the right axillary region a large painful lymph node was found. One daybefore the onset of the disease the patient had examined a dead calf. What is the most likely diagnosis?

  • A. Cutaneous anthrax
  • B. Bubonic plague
  • C. Carbuncle
  • D. Lymphocutaneous tularemia
Correct Answer: D

Rationale: The most likely diagnosis is D: Lymphocutaneous tularemia. The key clues include exposure to a dead animal, vesicle with serosanginous exudate, painless edema progressing to lymph node involvement, and fever. Tularemia is caused by Francisella tularensis, commonly acquired through contact with infected animals. The characteristic ulcer at the site of entry, lymphadenopathy, and systemic symptoms point towards tularemia. Cutaneous anthrax (A) presents with a painless ulcer and black eschar. Bubonic plague (B) typically presents with buboes (swollen lymph nodes) and fever. Carbuncle (C) is a deep skin infection typically caused by Staphylococcus aureus.

A bacteriological laboratory has been investigating a sample of homemade dried fish that was the cause of severe food poisoning. Microscopy of the culture inoculated in Kitt-Tarozzi medium revealed microorganisms resembling a tennis racket. What diagnosis can be made?

  • A. Botulism
  • B. Salmonellosis
  • C. Cholera
  • D. Dysentery
Correct Answer: A

Rationale: The correct answer is A: Botulism. The tennis racket appearance seen under the microscope is characteristic of Clostridium botulinum, the bacterium responsible for botulism. This bacterium produces spores that resemble a tennis racket shape. Botulism is a type of food poisoning caused by the ingestion of the toxin produced by Clostridium botulinum.

Summary:
B: Salmonellosis is caused by Salmonella bacteria, which do not exhibit a tennis racket appearance.
C: Cholera is caused by Vibrio cholerae, which also does not resemble a tennis racket under the microscope.
D: Dysentery is typically caused by bacteria such as Shigella or Entamoeba histolytica, neither of which exhibit the characteristic tennis racket appearance.

What is the primary purpose of a bacterial capsule?

  • A. Protein synthesis
  • B. Protection against desiccation
  • C. Enhancing virulence by preventing phagocytosis
  • D. Facilitating motility
Correct Answer: C

Rationale: The correct answer is C: Enhancing virulence by preventing phagocytosis. Bacterial capsules help bacteria evade the immune system by preventing phagocytosis, a process where immune cells engulf and destroy pathogens. This enhances the bacteria's virulence and ability to cause infections. Choices A, B, and D are incorrect because bacterial capsules do not directly contribute to protein synthesis, protect against desiccation, or facilitate motility.

Study of bacteriological sputum specimens stained by the Ziel-Neelsen method revealed some bright-red acid-resistant bacilli that were found in groups or singularly. When inoculated onto the nutrient media, the signs of their growth show up on the 10-15 day. These bacteria relate to the following family:

  • A. Micobacterium tuberculosis
  • B. Yersinia pseudotuberculosis
  • C. Histoplasma dubrosii
  • D. Klebsiella rhinoscleromatis
Correct Answer: A

Rationale: The correct answer is A: Mycobacterium tuberculosis.
1. Bright-red acid-resistant bacilli indicate the presence of mycolic acids in the cell wall, characteristic of Mycobacterium species.
2. Found in groups or singularly suggests the clumping nature of acid-fast bacilli.
3. Growth appearing after 10-15 days on nutrient media is consistent with the slow growth rate of Mycobacterium tuberculosis.
4. Yersinia pseudotuberculosis (B) and Klebsiella rhinoscleromatis (D) are not acid-fast bacilli and do not match the growth characteristics described.
5. Histoplasma dubrosii (C) is a fungus, not a bacterium, and does not exhibit acid-fast staining or the described growth pattern.

Antibiotics for multiple-resistant microorganisms are:

  • A. Ampicillin
  • B. Penicillin
  • C. Augmentin
  • D. Imipenem
Correct Answer: D

Rationale: The correct answer is D: Imipenem. Imipenem is a carbapenem antibiotic effective against multiple-resistant microorganisms due to its broad spectrum and resistance to beta-lactamases. It is often used as a last resort for severe infections.

Ampicillin (A) and Penicillin (B) are both beta-lactam antibiotics that are less effective against multiple-resistant microorganisms due to widespread resistance mechanisms. Augmentin (C) is a combination of amoxicillin and clavulanic acid, which may have limited efficacy against certain resistant strains but is not as effective as imipenem for treating infections caused by multiple-resistant microorganisms.

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