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A patient with a sore throat had a throat smear stained by Neisser's method. Microscopy revealed rods with polar dark blue granules. What microorganism is likely responsible?
- A. Corynebacterium diphtheriae
- B. Bacillus anthracis
- C. Clostridium tetani
- D. Escherichia coli
Correct Answer: A
Rationale: The presence of rods with polar dark blue granules stained by Neisser's method indicates metachromatic granules consistent with Corynebacterium diphtheriae. The characteristic staining pattern is due to the presence of polar granules in the bacterial cells, a feature specific to Corynebacterium diphtheriae. Bacillus anthracis, Clostridium tetani, and Escherichia coli do not exhibit this staining pattern or morphology typical of Corynebacterium diphtheriae, making them incorrect choices.
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Which of the following statements about in vitro cultivation of viruses is true?
- A. Viral cultivation under laboratory conditions is impossible
- B. Viruses are cultured on hen embryos, cell cultures and experimental animals
- C. Viruses are cultivated on special nutrient media
- D. Viruses are cultured only in human embryonic cell cultures
Correct Answer: B
Rationale: The correct answer is B because viruses can indeed be cultured on hen embryos, cell cultures, and experimental animals in vitro. This method allows for the replication and study of viruses outside the host organism. Option A is incorrect as viral cultivation is possible in laboratory settings. Option C is incorrect because while viruses can be grown on nutrient media, it is not the only method. Option D is incorrect as viruses can be cultured in various types of cell cultures, not just human embryonic ones.
Which of the following is a primary function of bacterial capsules?
- A. Energy production
- B. Protection from desiccation
- C. Adhesion and immune evasion
- D. DNA replication
Correct Answer: C
Rationale: The correct answer is C: Adhesion and immune evasion. Bacterial capsules serve as a protective layer that aids in adhesion to surfaces and host cells, allowing bacteria to colonize and evade the immune system. This function is crucial for bacterial survival and pathogenicity. Choices A and D are incorrect because energy production and DNA replication are not primary functions of bacterial capsules. Choice B is incorrect because while bacterial capsules do provide some protection from desiccation, their primary function lies in adhesion and immune evasion.
The key function of bacterial capsules is:
- A. facilitating motility
- B. resisting phagocytosis
- C. synthesizing DNA
- D. producing energy
Correct Answer: B
Rationale: The correct answer is B: resisting phagocytosis. Bacterial capsules are composed of polysaccharides that help bacteria evade phagocytosis by immune cells. This physical barrier prevents immune cells from engulfing and destroying the bacteria. Facilitating motility (A), synthesizing DNA (C), and producing energy (D) are not primary functions of bacterial capsules. Motility is usually facilitated by flagella, DNA synthesis occurs in the bacterial chromosome, and energy production is typically carried out by metabolic processes within the bacterial cell.
Which bacterial structure allows for attachment to host cells?
- A. Flagella
- B. Fimbriae
- C. Capsule
- D. Endospore
Correct Answer: B
Rationale: The correct answer is B: Fimbriae. Fimbriae are hair-like appendages found on the surface of bacteria that enable attachment to host cells. This attachment is crucial for establishing infection. Flagella (A) are used for movement, not attachment. Capsules (C) provide protection and help evade the host immune system, but do not directly facilitate attachment. Endospores (D) are dormant structures for survival, not for attachment to host cells. Fimbriae specifically aid in adherence to host cells, making them the correct choice in this context.
The causative agent of the disease gas gangrene Clostridium perfringens is:
- A. Gram-negative rod-shaped bacteria, fixed with capsule
- B. Gram-negative rod-shaped bacterium, motile, peritrichous without capsule
- C. Gram-positive rod-shaped bacterium, motile, peritrichous without capsule
- D. Gram-positive rod-shaped bacterium non-motile, with capsule
Correct Answer: C
Rationale: The correct answer is C because Clostridium perfringens is a Gram-positive rod-shaped bacterium, which matches the description provided. It is motile and peritrichous (having flagella all over the surface) without a capsule. This bacterium is known to cause gas gangrene due to its ability to produce toxins that destroy tissue.
Choice A is incorrect because Clostridium perfringens is Gram-positive, not Gram-negative, and it does not have a capsule. Choice B is incorrect because Clostridium perfringens is not motile and does not have flagella all over its surface. Choice D is incorrect because Clostridium perfringens is Gram-positive, not Gram-negative, and it is motile without a capsule.