Leptospira interrogans is a spirochete that can be cultured on selective media. Which of the following is the MOST appropriate culture medium for primary isolation of Leptospira?

Explanation

## Culture Media for Leptospira interrogans **Key Point:** Fletcher's semi-solid medium and EMJH (Ellinghausen-McCullough-Johnson-Harris) medium are the gold standard selective media for primary isolation and cultivation of Leptospira interrogans. **High-Yield:** Leptospira has unique nutritional requirements and grows slowly (generation time ~6–8 hours). It requires enriched media with specific supplements: ### Culture Media Characteristics | Medium | Type | Composition | Use | | --- | --- | --- | --- | | Fletcher's | Semi-solid | Rabbit serum, peptone, NaCl | Primary isolation, maintenance | | EMJH | Liquid | Vitamins, fatty acids, salts | Primary isolation, preferred | | Thayer-Martin | Selective | For Neisseria gonorrhoeae | Gram-negative cocci, NOT spirochetes | | LJ medium | Solid | For Mycobacterium tuberculosis | Acid-fast bacilli, NOT spirochetes | | Sabouraud agar | Fungal | For fungi and yeasts | NOT suitable for bacteria | **Clinical Pearl:** Leptospira grows best at 28–30°C in EMJH medium. Growth is slow, and cultures may take 2–4 weeks to become positive. Direct microscopy (dark-field) of clinical specimens is often faster for diagnosis. **Mnemonic:** **EMJH** = **E**llinghausen–**M**cCullough–**J**ohnson–**H**arris (remember: enriched, minimal contamination, for Leptospira)