For the selective isolation of Bordetella pertussis, which culture medium and incubation conditions are used?
- A MacConkey agar at 37°C for 24 hours — B. pertussis is gram-negative so grows on enteric media
- B Thayer-Martin medium (modified chocolate agar with VCN) under 5% CO2
- C Bordet-Gengou agar (BGA — potato infusion glycerol agar with sheep blood) or Regan-Lowe charcoal agar; incubated at 35–37°C for 5–7 days in humid conditions (organism is slow growing and fastidious) ✓
- D TCBS (thiosulfate-citrate-bile-sucrose) agar — selective for Bordetella species
Correct answer: C. Bordet-Gengou agar (BGA — potato infusion glycerol agar with sheep blood) or Regan-Lowe charcoal agar; incubated at 35–37°C for 5–7 days in humid conditions (organism is slow growing and fastidious)
Explanation
Bordetella pertussis is an extremely fastidious, slow-growing gram-negative coccobacillus that requires special culture media. The classical medium is Bordet-Gengou agar (charcoal blood agar), and the current preferred medium is Regan-Lowe charcoal agar with cephalexin (to suppress other respiratory flora). Incubation is at 35–37°C for 7–10 days with high humidity. Colonies appear as 'mercury droplets' or 'pearl drops.' NAAT (PCR) has largely replaced culture for acute diagnosis due to higher sensitivity. Thayer-Martin is for Neisseria; TCBS is for Vibrio.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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