Guess the Organism - Microbiology

1. Large, gray-white colonies with a double zone of beta-hemolysis on anaerobic blood agar. Gram stain reveals large, boxcar-shaped Gram-positive rods.

2. Small, creamy, beta-hemolytic colonies grow on blood agar. The organism is catalase positive, coagulase positive, and Gram stain reveals Gram-positive cocci in clusters.

3. A colony shows swarming motility on blood agar. The organism is oxidase negative and urease positive. It produces hydrogen sulfide on TSI agar.

4. Lactose-fermenting pink colonies grow on MacConkey agar. The organism is indole positive, oxidase negative, and Gram-negative rods are seen on staining.

5. Tiny gray colonies grow on chocolate agar but not on blood agar. Gram-negative coccobacilli are seen on Gram stain. The isolate requires both X and V factors.

6. Alpha-hemolytic colonies appear on blood agar. The isolate is catalase negative, optochin sensitive, and bile soluble. Gram-positive lancet-shaped diplococci are seen.

7. Beta-hemolytic colonies appear on blood agar. Catalase negative, bacitracin sensitive, Gram-positive cocci in chains.

8. Colonies have a mucoid appearance on MacConkey agar. The organism is urease positive, indole negative, oxidase negative.

9. A sputum culture yields colonies with a “breadcrumb-like” appearance. The organism is weakly acid-fast and filamentous on Gram stain.

10. A patient with HIV presents with meningitis. India ink staining of CSF reveals encapsulated yeast. Colonies grow on Sabouraud Dextrose Agar (SDA) and are urease positive.