Correct Answer: A

Rationale: Step 1: Treponema pallidum is a spirochete bacterium known to cause syphilis, a sexually transmitted infection. Step 2: Neisseria gonorrhoeae causes gonorrhea, not syphilis. Step 3: Chlamydia trachomatis is responsible for causing chlamydia, not syphilis. Step 4: Escherichia coli is commonly found in the gut and can cause gastrointestinal infections, not syphilis. Summary: Treponema pallidum is the correct answer as it is the specific bacterium associated with syphilis, while the other choices are responsible for different infections.

Correct Answer: C

Rationale: The correct answer is C: leg swelling. Endocarditis is an infection of the inner lining of the heart chambers and valves. Symptoms typically include fever, chills, weight loss, and muscle aches due to the body's immune response to the infection. Leg swelling is not a common symptom of endocarditis. It may occur in conditions like heart failure but is not directly associated with endocarditis. Therefore, choice C is the correct answer. Choices A, B, and D are incorrect because fever and chills, weight loss, and muscle aches are commonly seen in endocarditis due to the systemic inflammatory response to the infection.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. Rationale: 1. Gram-positive cocci in chains: S. pyogenes is a Gram-positive cocci in chains. 2. Catalase-negative: S. pyogenes is catalase-negative. 3. Beta-hemolytic: S. pyogenes exhibits beta-hemolysis. Summary of other choices: B: Streptococcus pneumoniae is alpha-hemolytic and optochin-sensitive. C: Enterococcus faecalis is catalase-negative, but not typically beta-hemolytic. D: Staphylococcus aureus is catalase-positive and coagulase-positive.

Correct Answer: A

Rationale: The correct answer is A: Metronidazole. It is the drug of choice for treating systemic amebiasis due to its high efficacy against Entamoeba histolytica. Metronidazole is well-absorbed, reaches therapeutic levels in the intestines, liver, and lungs, making it effective in treating the multi-organ involvement in this case. Choice B: Quiniofone is not a recommended treatment for amebiasis. Choice C: Tetracycline is not the first-line treatment for systemic amebiasis. Choice D: Quingamine is not a recognized drug for treating amebiasis.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci arranged in clusters, catalase-positive, and coagulase-negative characteristics are indicative of Staphylococcus species. Staphylococcus epidermidis is a common skin commensal that causes wound infections. Staphylococcus aureus is coagulase-positive and often causes more aggressive infections. Streptococcus pyogenes is catalase-negative and typically forms chains, not clusters. Enterococcus faecalis is catalase-negative and commonly found in the GI tract, not a common cause of wound infections.