ANALYSIS OF THE GENETIC-POLYMORPHISM OF BORRELIA-BURGDOFERI SENSU LATO BY MULTILOCUS ENZYME ELECTROPHORESIS

In recent years, Borrelia burgdorferi sensu late has been subdivided i nto three species, Borrelia burgdorferi sensu stricto, Borrelia garini i, and Borrelia afzelii, and a new species restricted to Japan, Borrel ia japonica, has been isolated from Ixodes ovatus, In addition, member s of several new genomic groups have been found in America and in Euro pe, suggesting that there are additional genospecies. In order to stud y the diversity of B. burgdorferi sensu lato, we analyzed 54 isolates cultured from humans and from different tick species and obtained from diverse geographic areas, including Europe, the United States, Japan, and the People's Republic of China, In order to investigate the genet ic relationship between microorganisms that are transmitted by soft ti cks and microorganisms that cause Lyme disease, we also included three strains of relapsing fever spirochetes. The method which we used was multilocus enzyme electrophoresis; 12 genetic loci mere characterized on the basis of the electrophoretic mobilities of their products, and 50 distinct allele profiles (electrophoretic types) were distinguished , The mean genetic diversity per locus was 0.747. A cluster analysis o f a matrix of genetic distances for pairs of electrophoretic types rev ealed 11 divisions that were separated at genetic distances greater th an 0.65. Five of these divisions corresponded to B. burgdorferi sensu stricto, B. garinii, B. afzelii, B. japonica, and the newly proposed s pecies ''Borrelia andersonii.'' Our results also confirmed that there are two additional genomic groups in Europe and at least one additiona l group in the United States. The relapsing fever spirochetes were not clearly separated from the spirochetes associated with Lyme disease, In conclusion, we believe that the previously proposed subdivision of B. burgdorferi sensu late into only four species should be reconsidere d.