Cultivation and virulence conversion of Borrelia duttonii in tissue cultures of SflEp cells

Sugiyama in this laboratory has established an in citro cultivation system on cenventional monolayer cultures of SflEp cells of Borrelia duttonii strain 406K which dose not grow well in cuurrently avilable media. The system, however, had some problems in the ability to support growth and virulence of the strain. In the present study, the author investigated the effects of sera added to Eagle's MEM on the growth and virulence of borreliae and developed a medified system. The results were as follows : 1. The mazimum yield of borreliae in the primary culture, 2.5×10^7 permilliliter, was obtained in MEM supplemented with 30% heat-inactivated (56℃, 30min) rabbit serum. Only 10 organisms per milliliter were required for initiating growth in the system. 2. Although commercial lots of untreated rabbit serum varied greatly in their ability to support growth of B. duttonii, those of heat-inactivated serum did not show such a variation. 3. Borreliae from the primary culture of the modified system showed only a little reduction of virulence for mice with the LD_<50> of 10^3-10^5organisms/ml. 4. In contrast to borreliae passaged in Sugiyama's, borreliae passaged through the medified system retained some virulence even after passages.