Polymerase chain reaction analyses identify two distinct classes of Borrelia burgdorferi.

We sequenced homologous chromosomal loci from several North American and European isolates of the Lyme disease spirochete Borrelia burgdorferi, as well as from the relapsing fever spirochete Borrelia hermsii. Inter- and intraspecies sequence comparisons permitted the design of B. burgdorferi-specific polymerase chain reaction primers that detected all strains tested (n = 31) from diverse geographical and biological origins. Polymerase chain reaction "typing" with other unique sets of primers subdivided B. burgdorferi isolates into two groups: all North American isolates and a few European isolates made up one group, while the majority of the European and Asian isolates made up the second group. This classification may have a clinical correlate reflected in differences between "typical" Lyme borreliosis in North America and Europe.