A culture from CSF of a 2-year-old yields fastidious Gram-negative coccobacilli requiring both hemin and NAD for growth on nutrient agar. The medium that supports its growth because heating blood releases these factors is:

• A Blood agar incubated anaerobically
• B Lowenstein-Jensen medium
• C Mueller-Hinton agar supplemented with sheep blood
• D Chocolate agar ✓

Explanation

Chocolate agar is prepared by gently heating blood agar to about 80°C, lysing erythrocytes and releasing factor X (hemin) and factor V (NAD), which Haemophilus influenzae requires for growth. Intact blood agar supplies factor V but sequesters factor X within red cells, so H. influenzae fails to grow there. Mueller-Hinton is a susceptibility testing base, and Lowenstein-Jensen is for mycobacteria.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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