DIVERSITY OF BORRELIA-BURGDORFERI SENSU LATO EVIDENCED BY RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM OF RRF (5S) RRL (23S) INTERGENIC SPACER AMPLICONS

The organization of the ribosomal genes is unique in Borrelia burgdorf eri in that the rrl (23S) and rrf (5S) genes are tandemly duplicated. We took advantage of this uniqueness to assess the restriction polymor phism of PCR products obtained with primers at the 3' end of the first rrf gene and at the 5' end of the second rrl gene. An amplicon that w as 226 to 266 bp long was generated from 99 of 100 B. burgdorferi sens u late strains. The nuclease MseI restriction polymorphism of the ampl icons provided a useful tool for identifying B. burgdorferi sensu stri cto, Borrelia garinii, Borrelia afzelii (formerly group VS461), and Bo rrelia japonica (formerly group F63B). Furthermore, it allowed us to r ecognize four new genomic groups, which were confirmed by DNA-DNA hybr idization data. Two of these genomic groups comprised European strains , and the other two groups contained American strains. The American ge nomic groups involved vectors with enzootic cycles quite different fro m those of B. burgdorferi sensu stricto, which previously was the only Lyme disease Borrelia species known to occur in the United States. Ou r method could be used for rapid screening of strain collections and f or epidemiological and medical purposes.