microbiology an evolving science test bank

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Specify the most commonly used parameters for autoclaving sterilization:

  • A. 1.0 atm., 120º C, 15-20min
  • B. 1.0 atm., 130º C, 10 hours
  • C. 1.5 atm., 135º C, 5min
  • D. 1.0 atm., 160º C, 1 hour
Correct Answer: A

Rationale: The correct answer is A because it specifies the commonly used parameters for autoclaving sterilization: 1.0 atm pressure, 120º C temperature, and 15-20 minutes duration. This combination ensures effective sterilization by providing the necessary heat and pressure for killing microorganisms.

Rationale:
1. Pressure of 1.0 atm: Standard atmospheric pressure commonly used in autoclaving.
2. Temperature of 120º C: Optimal temperature for sterilization without causing damage to heat-sensitive materials.
3. Duration of 15-20 minutes: Time required for heat and pressure to penetrate and kill microorganisms effectively.

Summary of Incorrect Choices:
B: Incorrect temperature and duration, too high and long, may damage materials.
C: Incorrect pressure and temperature, higher pressure and temperature not commonly used.
D: Incorrect temperature, too high, can damage materials, and duration is longer than necessary.

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Which of the following antibodies is synthesized by the infant soon after birth?

  • A. IgA
  • B. IgM
  • C. IgG
  • D. IgD
Correct Answer: B

Rationale: The correct answer is B: IgM. IgM is the first antibody synthesized by the infant soon after birth. It is produced by B cells in response to initial exposure to antigens. IgA is mainly found in mucosal areas, IgG is transferred from mother to fetus, and IgD functions in the early stages of B cell development. Therefore, IgM is the most suitable choice as the antibody synthesized by the infant soon after birth.

A patient with probable liver abscess was delivered to a surgical department. The patient for a long time had been on an assignment in an African country and had recurrent cases of gastrointestinal disturbance. What protozoan disease can it be?

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

Rationale: The correct answer is D: Amebiasis. The patient's symptoms of gastrointestinal disturbance and liver abscess are indicative of an infection with Entamoeba histolytica, the protozoan parasite responsible for amebiasis. The patient's travel history to an African country also increases the likelihood of contracting this disease, as it is more prevalent in tropical regions. Toxoplasmosis (A) is primarily associated with exposure to cat feces, Leishmaniasis (B) is transmitted through sandfly bites, and Malaria (C) is caused by Plasmodium parasites transmitted through mosquito bites. Therefore, these options are incorrect given the patient's presentation and travel history.

What microorganisms were accounted for in this case?

  • A. All bacteria that have grown on a nutrient medium
  • B. Opportunistic pathogenic bacteria
  • C. Enteropathogenic bacteria and viruses
  • D. Colibacilli
Correct Answer: C

Rationale: The correct answer is C because the case specifically mentions "enteropathogenic bacteria and viruses," indicating a focus on these specific microorganisms. Choice A is too broad and includes all bacteria, which is not specified in the case. Choice B mentions opportunistic pathogenic bacteria, which are not necessarily relevant to the case. Choice D specifies colibacilli, which may or may not be relevant to the case, but it is not as specific as choice C which clearly matches the information provided in the case.

Microscopic examination of a smear from a patient with gas gangrene revealed Gram-positive rods producing spores. What microorganism was identified?

  • A. Clostridium perfringens
  • B. Clostridium tetani
  • C. Bacillus anthracis
  • D. Clostridium botulinum
Correct Answer: A

Rationale: The correct answer is A: Clostridium perfringens. Gas gangrene is caused by Clostridium perfringens, a Gram-positive rod bacterium that produces spores. This bacterium is anaerobic and commonly found in soil, where it forms spores that can survive harsh conditions. Clostridium tetani causes tetanus, not gas gangrene. Bacillus anthracis causes anthrax, not gas gangrene. Clostridium botulinum causes botulism, not gas gangrene. Therefore, based on the characteristics of the microorganism described in the question, Clostridium perfringens is the correct identification.

A patient with acute food poisoning had fecal cultures grown on Endo agar, resulting in colorless colonies. What microorganism is most likely responsible?

  • A. Salmonella
  • B. Escherichia coli
  • C. Staphylococcus
  • D. Shigella
Correct Answer: A

Rationale: Step 1: Endo agar is a selective and differential media commonly used to isolate gram-negative bacteria.
Step 2: Colorless colonies on Endo agar indicate the absence of lactose fermentation.
Step 3: Salmonella is a gram-negative bacterium that does not ferment lactose, leading to colorless colonies on Endo agar.
Step 4: Therefore, the correct answer is A: Salmonella.
Summary:
B: Escherichia coli ferments lactose, producing pink colonies on Endo agar.
C: Staphylococcus is a gram-positive bacterium and would not grow on Endo agar.
D: Shigella is a gram-negative bacterium but ferments lactose, resulting in pink colonies on Endo agar.

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