SERA FROM OSPA-VACCINATED DOGS, BUT NOT THOSE FROM TICK-INFECTED DOGS, INHIBIT IN-VITRO GROWTH OF BORRELIA-BURGDORFERI

Dogs were challenged with Borrelia burgdorferi by exposure to ticks, w ith or without prior protection from infection by recombinant OspA (rO spA) vaccination. Sera from these dogs were tested for their capabilit y to inhibit the growth of B. burgdorferi in vitro, Bacterial growth w as detected by a color change in the culture medium, and the optical d ensity was measured with a spectrophotometer in microtiter plates. By growth inhibition, which was complement dependent, the color change wa s lacking after 5 days of incubation. Over a 1-year study, nonvaccinat ed dogs infected by exposure to ticks showed high antibody titers to B . burgdorferi by kinetic enzyme-linked immunosorbent assay (KELA). The same sera did not inhibit spirochetal growth or did so only at a low dilution. These results corresponded to the lack of OspA and OspB anti bodies seen in Western blots (immunoblots), and these dogs were not pr otected from infection or disease. In contrast, dogs immunized with rO spA prior to challenge with infected ticks produced high antibody tite rs, as determined by KELA, but their sera also had high growth-inhibit ing antibody titers. Western blot analysis showed a strong band in the 32-kDa region when the sera of these dogs were tested. When adjuvant was administered with rOspA, antibody titers by both KELA and growth i nhibition were higher and persisted longer in the immunized dogs, All dogs immunized with rOspA were protected from infection and disease.