Medical Microbiology Test Bank

Correct Answer: B

Rationale: The correct answer is B: Malaria. Fever developing 2 weeks post-blood transfusion is characteristic of malaria due to the incubation period of the parasite. Trypanosomiasis presents earlier, amebiasis usually causes GI symptoms, and toxoplasmosis typically manifests with flu-like symptoms. Malaria is the most likely cause based on the timing and clinical presentation.

Correct Answer: B

Rationale: The correct answer is B because humoral immunity involves the formation of specific antibodies by B cells. B cells differentiate into plasma cells that produce antibodies to target specific antigens. T cells are involved in cell-mediated immunity, not humoral immunity. Choice A is incorrect because T cells do not produce antibodies. Choice C is incorrect as only B cells are responsible for antibody production in humoral immunity. Choice D is incorrect as B cells play a crucial role in the humoral immune response.

Correct Answer: A

Rationale: The correct answer is A: Clostridium botulinum. This bacterium is responsible for causing botulism due to its production of botulinum toxin, which is one of the most potent neurotoxins known. Clostridium botulinum thrives in anaerobic conditions like improperly canned foods. Staphylococcus aureus (B), Bacillus anthracis (C), and Pseudomonas aeruginosa (D) do not produce the botulinum toxin and are not associated with botulism. Staphylococcus aureus is known for causing food poisoning, Bacillus anthracis for anthrax, and Pseudomonas aeruginosa for various infections, but not botulism.

Correct Answer: C

Rationale: The correct answer is C: tapeworms. Taeniasis is specifically caused by tapeworms of the Taenia species, such as Taenia solium. These parasitic worms infect the intestines of humans through consumption of contaminated food or water. Ringworms (choice A), hookworms (choice B), and pinworms (choice D) are all different types of parasites that cause distinct infections in the body, not taeniasis. Tapeworms are the only organisms among the choices that are directly associated with taeniasis due to their unique life cycle and mode of infection.

Correct Answer: B

Rationale: Correct Answer: B - Plasmids are circular DNA molecules Rationale: 1. Plasmids are extrachromosomal DNA molecules found in bacteria. 2. Plasmids are typically circular in structure, not linear. 3. Circular plasmids are easily replicated and transferred between bacteria. 4. Plasmids can carry genes for antibiotic resistance, making option C incorrect. 5. Not all bacteria have plasmids, making option D incorrect. 6. While plasmids can provide benefits, they are not essential for bacterial survival, making option A incorrect.