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?
- A Neisseria gonorrhoeae
- B Moraxella catarrhalis
- C Neisseria meningitidis ✓
- D Haemophilus influenzae
Correct answer: C. Neisseria meningitidis
Explanation
Neisseria meningitidis ferments both glucose and maltose, distinguishing it from N. gonorrhoeae which ferments only glucose. It grows on chocolate agar and requires warm incubation. H. influenzae is a small Gram-negative coccobacillus, not a diplococcus. Moraxella catarrhalis is oxidase positive but does not ferment carbohydrates. Maltose fermentation is the key differentiator between the two Neisseria species causing human disease.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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