Cultivation at 37 degrees C enhances Borrelia burgdorferi sensu stricto infectivity for hamsters.

Borrelia burgdorferi sensu stricto (s.s.), the causative agent of Lyme disease in North America is transmitted to the mammalian host by ticks belonging to the genus, Ixodes. Antibodies to several spirochetal proteins, most notably outer surface protein C (OspC), have been observed in early infection in both humans and laboratory animals. Thus, the expression of these proteins have been postulated to play a role in tick transmission and spirochetal infectivity for the mammalian host. B. burgdorferi strain JMNT was induced to produce increased levels of OspC by cultivation in BSK medium at 37 degrees C. To diminish expression of OspC, spirochetes were cultivated at 31 degrees C. Spirochetes shifted down from 37 degrees C to 31 degrees C or up from 31 degrees C to 37 degrees C for 1 week contained equivalent amounts of OspC. To evaluate spirochetal infectivity, hamsters were inoculated subcutaneously with 1 x 10(4) or 1 x 10(6) spirochetes grown at the above-mentioned temperatures. Hamsters inoculated with spirochetes expressing high amounts of OspC all became infected, irrespective of the inoculum size. None of the hamsters inoculated with 1 x 10(4) spirochetes grown at 31 degrees C or in cultures shifted down from 37 degrees C to 31 degrees C were infected. All infected hamsters, confirmed by isolation of spirochetes in ear and/or bladder cultures, had an antibody response to OspC. In contrast, all non-infected hamsters lacked antibodies to OspC. We conclude that cultivation of spirochetes at 37 degrees C enhances their infectivity for hamsters. This study also suggests there is a correlation between enhancement of OspC expression and spirochetal infectivity for hamsters.