Comparison of growth and morphology of Borrelia burgdorferi sensu lato in BSK‐H and BSK‐II media stored for prolonged periods

Barbour‐Stoenner‐Kelly II (BSK‐II) and BSK‐H media were used for cultivation and isolation of fastidious Borrelia species ‐ the causative agents of Lyme borreliosis. Culture media have a limited shelf life and require adequate storage. Our goal was to assess how the growth of Borrelia would be affected by prolonged storage of media and inadequate storage conditions (BSK‐H stored at +4 °C for 2.5 years and BSK‐II stored at −20 °C for 11 years). Growth of different Borrelia afzelii, Borrelia garinii, Borrelia lusitaniae and Borrelia valaisiana strains was assessed during 2 weeks of incubation at 33 °C. Monitored parameters included cell count per mL, morphology and motility. The results of this study have shown weaker growth of borrelia strains in BSK‐H at +4 °C (median final cell number of 1.5 × 106/mL) than in BSK‐II at −20 °C (median final cell number of 7.75 × 106/mL) and in fresh BSK‐H media (median final cell number of 8.95 × 106/mL). Duration of storage of media had no impact on Borrelia morphology and motility. Our results indicate that temperature of −20 °C is optimal for long‐term storage of medium, BSK‐II stored for 11 years provided effective support to growth of Borrelia and may be employed for cultivation.