Bacteriology MCQs

Microbiology · 6 free questions with answers & explanations.

1. A 55-year-old diabetic male presents with rapidly spreading necrosis of the scrotal and perineal skin with crepitus. Blood cultures grow a Gram-positive, spore-forming, anaerobic bacillus that produces a lecithinase (alpha toxin) demonstrating a positive Nagler reaction. Which organism is MOST likely responsible?
2. A 19-year-old college student presents with meningitis. Gram staining of CSF shows Gram-negative diplococci. The organism grows on chocolate agar but not on blood agar at room temperature. It is oxidase positive and ferments glucose and maltose but NOT lactose or sucrose. Which organism is most likely?
3. A 30-year-old veterinarian develops a skin papule on his hand 10 days after handling stillborn lambs, which slowly enlarges into a painless haemorrhagic blister with central necrosis and marked oedema but absent local tenderness. Gram stain of lesion exudate shows large Gram-positive rods. The MOST likely diagnosis is:
4. Which of the following selective culture media is used for the primary isolation of Vibrio cholerae from stool samples?
5. A 45-year-old chronic alcoholic presents with a productive cough, blood-tinged 'currant jelly' sputum, and lobar consolidation on chest X-ray. Gram stain shows Gram-negative, mucoid rods in short chains. The organism is urease positive and shows a positive string test. Which organism is the most likely causative agent?
6. A 22-year-old sexually active woman presents with lower abdominal pain, cervical motion tenderness, and mucopurulent cervical discharge. Gram stain of the discharge shows Gram-negative intracellular diplococci within PMNs. Culture on Thayer-Martin medium shows oxidase-positive colonies. The organism ferments glucose but NOT maltose. Which organism is responsible?