CULTURING SELECTS FOR SPECIFIC GENOTYPES OF BORRELIA-BURGDORFERI IN AN ENZOOTIC CYCLE IN COLORADO

In Colorado, Borrelia burgdorferi sensu stricto, the etiologic agent o f Lyme disease, is maintained in an enzootic cycle between Ixodes spin ipalpis ticks and Neotoma mexicana rats (27). The frequencies of flage llin (fla), 66-kDa protein (p66), and outer surface protein A (ospA) a lleles were examined in 71 B. burgdorferi isolates from samples from C olorado. Approximately two-thirds of these samples were isolates from I, spinipalpis ticks that had been cultured in BSK-H medium prior to D NA extraction, The remaining samples were from total DNA extracted dir ectly from infected I. spinipalpis ticks, A portion of each gene was a mplified by PCR and screened for genetic variability by single-strand conformation polymorphism (SSCP) analysis, We identified three alleles in the fla gene, seven in the p66 gene, and seven in the ospA gene, S equencing verified that the amplified products originated from B. burg dorferi template DNA and indicated 100% sensitivity and specificity of the SSCP analysis, The frequencies of the p66 and ospA alleles were s ignificantly different between cultured and uncultured spirochetes, Th e number of three-locus genotypes and the genetic diversity of alleles at all loci were consistently lower in cultured spirochetes, suggesti ng that culturing of B. burgdorferi in BSK-H medium may select for spe cific genotypes.