A construction worker from Kerala develops acute febrile illness with conjunctival suffusion, calf muscle tenderness, thrombocytopaenia, and renal dysfunction after flooding. Leptospira IgM ELISA is positive. Which culture medium and incubation conditions are used to isolate Leptospira from blood in the first week of illness?
- A BACTEC blood culture bottles at 37°C for 5 days with standard protocol
- B EMJH (Ellinghausen-McCullough-Johnson-Harris) liquid medium at 28–30°C for up to 13 weeks with dark-field microscopy surveillance ✓
- C Tryptic soy broth at 37°C with 5% CO2 for 48 hours
- D Charcoal-yeast extract agar (CYE) at 35°C for 7–10 days
Explanation
Leptospira are fastidious, slowly growing aerobic spirochaetes requiring specialised culture media. EMJH semi-solid liquid medium (also Fletcher's or Korthof's medium) enriched with rabbit serum albumin/Tween 80 is the standard isolation medium. Incubation is at 28–30°C (not 37°C, which inhibits growth) for up to 13 weeks with twice-weekly dark-field microscopy examination. Blood culture is most productive in the first 10 days (leptospiraemia phase). Standard BACTEC will not grow Leptospira. EMJH is also used for urine culture (from week 2 onwards). RT-PCR on blood is now preferred over culture for rapid diagnosis.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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