Microbiology Test Bank

Correct Answer: A

Rationale: Step-by-step rationale: 1. Anopheles mosquitoes are the primary vectors for transmitting malaria. 2. They prefer stagnant water for breeding, common in tropical regions. 3. Culex mosquitoes primarily spread diseases like West Nile virus. 4. Aedes mosquitoes transmit diseases like Zika and dengue fever. 5. Mansonia mosquitoes are known for transmitting filarial diseases. Therefore, the correct answer is A (Anopheles), as they are specifically associated with spreading malaria.

Correct Answer: A

Rationale: The correct choice is A: Binding to IgE fixed to mast cells. The Besredka desensitization method involves injecting small, gradually increasing doses of the allergen to induce tolerance and prevent anaphylactic shock. This process works by binding the allergen to IgE antibodies fixed to mast cells, which prevents the release of histamine and other inflammatory mediators that trigger allergic reactions. This desensitization process helps the immune system become less reactive to the allergen over time. Incorrect choices: B: Inhibited synthesis of mast cells mediators - This choice does not reflect the mechanism of the Besredka desensitization method, which involves binding to IgE on mast cells. C: Stimulation of the immunological antigen tolerance - While this may sound plausible, the Besredka method specifically targets the IgE-mast cell interaction. D: Stimulation of antigen-specific IgG synthesis - While IgG antibodies may play a role in desensitization, the

Correct Answer: D

Rationale: The correct answer is D: Binary fission. Binary fission is a method of bacterial cell division, not a method of acquiring genetic material. Transformation, conjugation, and transduction are mechanisms through which bacteria can acquire genetic material from other sources. Transformation involves the uptake of naked DNA from the environment, conjugation is the transfer of genetic material through direct cell-to-cell contact, and transduction is the transfer of genetic material via bacteriophages. Therefore, binary fission is the only option that does not involve the acquisition of new genetic material.

Correct Answer: A

Rationale: The correct answer is A because penicillins and cephalosporins inactivate transpeptidase activity of penicillin binding proteins, leading to disruption of bacterial cell wall synthesis. This mechanism makes them bactericidal, not bacteriostatic (choice B). Choice C is incorrect as penicillins and cephalosporins target cell wall synthesis, not the cytoplasmic membrane. Choice D is incorrect as option A is the correct statement.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Purple-stained diplococci suggest Gram-positive cocci. 2. Capsule presence is a characteristic of Streptococcus pneumoniae. 3. S. pneumoniae is known to form diplococci arrangements. 4. Therefore, the microorganism most likely present is Streptococcus pneumoniae. Summary: - B: Klebsiella pneumoniae is a Gram-negative rod, not a cocci. - C: Neisseria meningitidis is a Gram-negative diplococcus, not a capsule producer. - D: Escherichia coli is a Gram-negative rod, not a cocci or capsule producer.