Foundations in Microbiology Test Bank

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There are several cases of children from boarding school suffering from sore throat. Microscopy of tonsil smears stained according Neisser method has revealed thin yellow bacilli with dark brown grains on their ends placed in the shape of Roman numeral five. What infection can be suspected in this case?

  • A. Diphtheria
  • B. Scarlet fever
  • C. Listeriosis
  • D. Tonsilitis
Correct Answer: A

Rationale: Rationale for Correct Answer A (Diphtheria):
1. Thin yellow bacilli with dark brown grains on ends suggest Corynebacterium diphtheriae, characteristic of diphtheria.
2. Roman numeral five shape is typical of diphtheria bacilli.
3. Diphtheria causes sore throat and can spread in boarding schools.
4. Neisser staining method is used for diphtheria bacilli.
Summary of Incorrect Choices:
B: Scarlet fever is caused by Streptococcus pyogenes and presents with rash, not yellow bacilli.
C: Listeriosis is caused by Listeria monocytogenes, not consistent with the described findings.
D: Tonsillitis can be caused by various bacteria or viruses, but the specific characteristics described do not match.

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Which of the following bacteria is known for producing a toxin that causes botulism?

  • A. Clostridium botulinum
  • B. Clostridium tetani
  • C. Staphylococcus aureus
  • D. Neisseria gonorrhoeae
Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium is known for producing botulinum toxin, which causes botulism. It is an anaerobic, spore-forming bacterium commonly found in soil. Clostridium tetani causes tetanus, not botulism. Staphylococcus aureus can cause food poisoning but not botulism. Neisseria gonorrhoeae is responsible for gonorrhea, not botulism. Therefore, A is the correct answer due to the specific association of Clostridium botulinum with botulism toxin production.

A defined microorganism can be isolated in pure culture:

  • A. From liquid and solid media
  • B. From liquid nutrient media
  • C. Only from single colonies on solid media
  • D. None of the above
Correct Answer: C

Rationale: The correct answer is C because isolating a defined microorganism in pure culture involves obtaining a single, distinct colony on solid media. This ensures that only one type of microorganism is present in the culture, preventing contamination. Liquid media can harbor multiple organisms, making it challenging to isolate a specific microorganism. Therefore, choice A is incorrect. Choice B is also incorrect as liquid nutrient media does not provide the necessary isolation required for pure culture. Choice D is incorrect because isolating from single colonies on solid media allows for the pure culture of the defined microorganism.

During sanitary and bacteriological testing of water with the membrane filter technique there were revealed two red colonies on a membrane filter (Endo agar) through which 500 ml of water was filtred. Calculate the coli index and coli titer of the analyzed water:

  • A. 4 and 250
  • B. 2 and 500
  • C. 250 and 4
  • D. 500 and 2
Correct Answer: C

Rationale: The correct answer is C (coli index of 250 and coli titer of 4). The coli index is calculated by multiplying the number of colonies by the reciprocal of the volume filtered, which gives 2 colonies x (1/0.5 L) = 4. The coli titer is obtained by dividing the volume filtered by the number of colonies, which gives 0.5 L / 2 colonies = 0.25 L or 250 ml. This indicates the concentration of coliform bacteria in the water sample.

Choice A (4 and 250) is incorrect because it has the correct coli index but the values are reversed for coli index and coli titer. Choice B (2 and 500) is incorrect as it provides the correct coli titer value but the values are reversed for coli index and coli titer. Choice D (500 and 2) is incorrect because it reverses the values for both coli index and coli titer.

When a smear is stained by Burri-Gins method a mucous structure that is tightly bound with the cellular wall of bacteria and has well-defined outer boundaries can be detected. This element of a bacteria cell is called:

  • A. Capsule
  • B. Spore
  • C. Filaments
  • D. Ribosomes
Correct Answer: A

Rationale: The correct answer is A: Capsule. A capsule is a mucous structure tightly bound to the bacterial cell wall with distinct outer boundaries. This structure helps bacteria evade the host immune system, resist desiccation, and adhere to surfaces. In contrast, spores are resistant structures formed by certain bacteria for survival, filaments are long chains of bacterial cells, and ribosomes are cellular organelles responsible for protein synthesis. Therefore, based on the characteristics described in the question, the most appropriate choice is A: Capsule.

After the transfer of the F plasmid from the donor to the recipient cell..

  • A. It is not possible to predict the outcome
  • B. The donor cells become F
  • C. The two cells become F
  • D. The two cells become F+
Correct Answer: D

Rationale: After the transfer of the F plasmid from the donor to the recipient cell, the correct answer is D. This is because the F plasmid carries genes for conjugation, allowing the recipient cell to become F+ (containing the F plasmid). The donor cell remains F. Choice A is incorrect as the outcome can be predicted based on the transfer of the F plasmid. Choice B is incorrect because the donor cell does not become F after transferring the F plasmid. Choice C is incorrect as only the recipient cell becomes F+, not both cells.

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