Chancroid is caused by Haemophilus ducreyi. Which culture medium is used for isolation, and what is the characteristic colonial morphology?

• A Thayer-Martin medium; oxidase-positive colonies
• B Lowenstein-Jensen medium; buff-coloured slow-growing colonies
• C Chocolate agar; satellite phenomenon around Staphylococcus streak
• D Hammond's medium (GC agar + vancomycin + fetal calf serum); school-of-fish pattern on Gram stain ✓

Explanation

H. ducreyi grows on enriched selective media such as GC agar base with vancomycin and fetal calf serum (Hammond's medium) or Mueller-Hinton agar with similar supplements. On Gram stain from the ulcer exudate, the organisms appear in the classic 'school of fish' or 'railroad track' pattern — small gram-negative coccobacilli in parallel chains. Thayer-Martin is used for N. gonorrhoeae, and the satellite phenomenon is used to identify H. influenzae (not H. ducreyi).

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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