The successful isolation and cultivation of Lyme disease spirochetes began with early attempts to cultivate relapsing fever borreliae. Observations on the growth of Lyme disease spirochetes under different in vitro conditions may provide insights into their metabolic characteristics and the pathogenesis of Lyme disease. The isolation and in vitro cultivation of previously unknown spirochetes from ixodid ticks, mammals, and patients with Lyme disease were built upon earlier research. Noguchi's work at the Rockefeller Institute demonstrated that relapsing fever borreliae could be maintained in vitro, and his medium, based on human ascitic fluid, provided a foundation for later formulations. Kligler and Robertson later defined conditions for maintaining and growing these spirochetes in derivatives of Noguchi's medium, noting the importance of pH, buffer, and nutrients. Kelly's medium, which included a buffer system, salts, glucose, pyruvate, gelatin, and N-acetylglucosamine, allowed the successful propagation of Borrelia hermsii. Stoenner improved this medium by adding Yeastolate and CMRL 1066 to support the growth of Borrelia hermsii. The author learned the science of cultivating borreliae from Stoenner and later isolated a spirochete from Ixodes dammini ticks. This spirochete was cultivated in Stoenner's medium and later designated as strain B31. Further modifications led to the development of BSK II, a medium that supports the growth of Lyme disease spirochetes and relapsing fever borreliae. The author found that BSK II was essential for the growth of Lyme disease spirochetes, while relapsing fever borreliae were more sensitive to changes in the medium. The optimal temperature for in vitro cultivation of Lyme disease spirochetes is between 30–37°C, with growth slowing at 39°C and ceasing at 40°C. The ability of these spirochetes to grow in solid medium suggests their potential to grow in tissues. The author also noted that Lyme disease spirochetes tend to grow in large aggregates, which may reflect important in vivo phenomena such as tissue binding and resistance to phagocytosis. The development of BSK II has been crucial for the cultivation of Lyme disease spirochetes, and further research may lead to more simplified media.The successful isolation and cultivation of Lyme disease spirochetes began with early attempts to cultivate relapsing fever borreliae. Observations on the growth of Lyme disease spirochetes under different in vitro conditions may provide insights into their metabolic characteristics and the pathogenesis of Lyme disease. The isolation and in vitro cultivation of previously unknown spirochetes from ixodid ticks, mammals, and patients with Lyme disease were built upon earlier research. Noguchi's work at the Rockefeller Institute demonstrated that relapsing fever borreliae could be maintained in vitro, and his medium, based on human ascitic fluid, provided a foundation for later formulations. Kligler and Robertson later defined conditions for maintaining and growing these spirochetes in derivatives of Noguchi's medium, noting the importance of pH, buffer, and nutrients. Kelly's medium, which included a buffer system, salts, glucose, pyruvate, gelatin, and N-acetylglucosamine, allowed the successful propagation of Borrelia hermsii. Stoenner improved this medium by adding Yeastolate and CMRL 1066 to support the growth of Borrelia hermsii. The author learned the science of cultivating borreliae from Stoenner and later isolated a spirochete from Ixodes dammini ticks. This spirochete was cultivated in Stoenner's medium and later designated as strain B31. Further modifications led to the development of BSK II, a medium that supports the growth of Lyme disease spirochetes and relapsing fever borreliae. The author found that BSK II was essential for the growth of Lyme disease spirochetes, while relapsing fever borreliae were more sensitive to changes in the medium. The optimal temperature for in vitro cultivation of Lyme disease spirochetes is between 30–37°C, with growth slowing at 39°C and ceasing at 40°C. The ability of these spirochetes to grow in solid medium suggests their potential to grow in tissues. The author also noted that Lyme disease spirochetes tend to grow in large aggregates, which may reflect important in vivo phenomena such as tissue binding and resistance to phagocytosis. The development of BSK II has been crucial for the cultivation of Lyme disease spirochetes, and further research may lead to more simplified media.