Classification of Italian isolates of Borrelia burgdorferi into three genomic groups.

In this study we investigated the genotypic characteristics of some locally isolated strains of B. burgdorferi by three different methodologies: restriction endonuclease analysis (REA), Southern blot hybridization with whole DNAs from Borrelia strains and Southern blot hybridization with rRNA 16 + 23S genes derived from E. coli. REA fingerprintings were evaluated by cluster analysis, according to the principles of numerical taxonomy. The genomas of the locally isolated strains were compared with borreliae originating from different countries of Europe, including Sweden and with the American reference strain B31. Among the European strains, some already described by Baranton (Baranton et al., 1992) as representatives of different genomic groups Borrelia sensu stricto and Borrelia garinii were used. By the different techniques the isolates were included in three genomic groups which could correspond to the three genospecies identified by Baranton, namely B. burgdorferi sensu stricto, B. garinii and B. group VS461: in fact two strains were included in a homogeneous group, probably corresponding to the VS461 genomic group, together with other European borreliae; one isolate was included in a group consisting of B31 and some other European strains already described as belonging to Borrelia burgdorferi in sensu stricto. Finally two isolates were ascribed to a third genomic group probably corresponding to the genospecies indicated as Borrelia garinii. These findings indicate that a small number of Borrelia strains isolated from a very restricted area can be genetically heterogeneous.