Correct Answer: A

Rationale: The correct answer is A: Protozoa. Protozoa are eukaryotic microorganisms, meaning they have a true nucleus and membrane-bound organelles. This relates to the question as eukaryotes are organisms with complex cells containing these features. Viruses (B) are non-living entities that require a host cell to replicate, lacking cellular structures. Viroids (C) are smaller than viruses and consist of only RNA, lacking a protein coat. Prions (D) are misfolded proteins causing diseases but are not considered microorganisms nor do they have cellular structure. Thus, protozoa are the only eukaryotic microorganism group among the options.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci in clusters that are catalase-positive and coagulase-negative points towards coagulase-negative staphylococci like Staphylococcus epidermidis. Staphylococcus aureus is catalase-positive and coagulase-positive. Streptococcus pyogenes is catalase-negative. Enterococcus faecalis is catalase-negative and not typically seen in clusters. Therefore, the most likely causative agent in this scenario is Staphylococcus epidermidis.

Correct Answer: B

Rationale: The correct answer is B: Trimethoprim. Trimethoprim is a folate antagonist that inhibits dihydrofolate reductase, an enzyme essential for folate metabolism in bacteria. This disrupts bacterial DNA synthesis, leading to bacteriostatic effects. Methyl Penicillin (A) is a beta-lactam antibiotic that interferes with bacterial cell wall synthesis. Vancomycin (C) inhibits cell wall synthesis by binding to D-Ala-D-Ala terminus of cell wall precursors. Gentamicin (D) inhibits bacterial protein synthesis by binding to the 30S subunit of the bacterial ribosome.

Correct Answer: A

Rationale: Step 1: Streptococcus pyogenes is commonly known as Group A Streptococcus, which is the primary bacteria responsible for causing strep throat. Step 2: Staphylococcus aureus is not typically associated with strep throat but can cause skin infections and other illnesses. Step 3: Neisseria gonorrhoeae is the bacteria responsible for gonorrhea, a sexually transmitted infection, not strep throat. Step 4: Clostridium tetani causes tetanus, a bacterial infection that affects the nervous system and is not related to strep throat.

Correct Answer: A

Rationale: The correct answer is A: Co-trimoxazole. This drug combination is the first-line treatment for toxoplasmosis due to its efficacy against Toxoplasma gondii. Co-trimoxazole consists of sulfamethoxazole and trimethoprim, which work synergistically to inhibit bacterial and protozoal folate synthesis, effectively treating toxoplasmosis. B: Itraconazole is an antifungal medication and not effective against toxoplasmosis. C: Mebendazole is an anthelmintic drug used for treating parasitic worm infections, not toxoplasmosis. D: Azidothimidine, also known as AZT, is used for treating HIV, not toxoplasmosis.