A wound culture from a patient with an infected ulcer revealed Gram-positive cocci in clusters. The bacteria were catalase-positive and coagulase-negative. What is the most likely causative agent?

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus epidermidis. The presence of Gram-positive cocci in clusters, catalase-positive, and coagulase-negative characteristics indicate Staphylococcus species. Specifically, Staphylococcus epidermidis is a common skin commensal and a frequent cause of wound infections. Staphylococcus aureus is catalase-positive and coagulase-positive, making it less likely in this scenario. Streptococcus pyogenes and Enterococcus faecalis are both Gram-positive cocci but are catalase-negative, making them less likely causative agents.

Correct Answer: A

Rationale: The correct answer is A: Facultative anaerobes. Facultative anaerobes can survive in both aerobic and anaerobic conditions because they have the metabolic flexibility to switch between utilizing oxygen for respiration in aerobic conditions and using fermentation in anaerobic conditions. Obligate aerobes (B) require oxygen for survival, obligate anaerobes (C) cannot survive in the presence of oxygen, and microaerophiles (D) require low levels of oxygen to grow effectively. Therefore, the ability of facultative anaerobes to adapt to varying oxygen levels makes them the correct choice for this question.

Correct Answer: B

Rationale: The correct answer is B: Bordetella pertussis. This bacterium causes whooping cough by infecting the respiratory tract. It produces toxins that lead to severe coughing fits characteristic of the disease. Clostridium botulinum (A) causes botulism, Streptococcus pneumoniae (C) causes pneumonia, and Neisseria meningitidis (D) causes meningitis, not whooping cough. B. pertussis is the only bacterium specifically associated with whooping cough.

Correct Answer: A

Rationale: The correct answer is A: Treponema pallidum. This bacterium is responsible for causing syphilis due to its unique spiral shape and ability to penetrate intact mucous membranes. It is transmitted through sexual contact or from mother to child during pregnancy. Neisseria gonorrhoeae causes gonorrhea, Chlamydia trachomatis causes chlamydia, and Escherichia coli is a common bacterium found in the gut and not associated with syphilis. Treponema pallidum's specific characteristics and mode of transmission distinguish it from the other choices, making it the correct answer.

Correct Answer: C

Rationale: The correct answer is C: Louis Pasteur. He conducted experiments that definitively disproved the theory of spontaneous generation through his famous swan-neck flask experiment. By showing that microorganisms only appeared in the broth when exposed to air, Pasteur demonstrated that they did not arise spontaneously. John Needham's experiments were inconclusive, Joseph Lister is known for his contributions to antiseptic surgery, and Robert Koch is credited with developing Koch's postulates for identifying the causative agents of diseases, but neither of them directly contributed to ending the controversy about spontaneous generation.