MCB 2000 Microbiology Final Exam Review Q & A 2026 (Complete And Verified Study material) (20pages) LEARNEXAMS

1. A patient presents with a wound infection, and a Gram stain reveals gram-positive cocci in clusters. Which organism is most likely responsible, and what is the rationale for antibiotic therapy? - A) Staphylococcus aureus; produces exotoxins and has a high prevalence in skin infections. - B) Streptococcus pyogenes; commonly associated with throat infections. - C) Enterococcus faecalis; typically found in the gastrointestinal tract. - D) Staphylococcus epidermidis; part of the normal skin flora. Answer: A) Staphylococcus aureus; it is the most common cause of wound infections due to its ability to produce exotoxins and its prevalence in skin infections, making it a critical target for antibiotic therapy. 2. During a tuberculosis outbreak, a nursing student asks why Mycobacterium tuberculosis is difficult to treat. Which of the following is the most accurate response? - A) It has a slow generation time, leading to delayed symptom presentation. - B) It forms spores, which are resistant to environmental stresses. - C) It possesses a mycolic acid cell wall, contributing to antibiotic resistance. - D) It is an obligate anaerobe, complicating treatment options. Answer: C) It possesses a mycolic acid cell wall, which is waxy and impermeable to many antibiotics, making treatment difficult and prolonged. 3. A 65-year-old patient with pneumonia has a sputum sample positive for gram-negative rods. Which pathogen is most likely, and what is the firstline treatment? - A) Haemophilus influenzae; ampicillin. - B) Klebsiella pneumoniae; ceftriaxone. - C) Pseudomonas aeruginosa; ciprofloxacin. - D) Escherichia coli; trimethoprim-sulfamethoxazole. Answer: B) Klebsiella pneumoniae; it is a common cause of pneumonia in elderly patients and ceftriaxone is the first-line treatment due to its effectiveness against gram-negative pathogens. 4. In a case of suspected septicemia, blood cultures are drawn. Why is it