Borrelia burgdorferi sensu stricto is clonal in patients with early Lyme borreliosis

Abstract

Lyme borreliosis, the most commonly reported vector-borne disease in North America, is caused by the spirochete Borrelia burgdorferi. Given the extensive genetic polymorphism of B. burgdorferi, elucidation of the population genetic structure of the bacterium in clinical samples may be relevant for understanding disease pathogenesis and may have applicability for the development of diagnostic tests and vaccine preparations. In this investigation, the genetic polymorphism of the 16S-23S rRNA (rrs-rrlA) intergenic spacer and ospC was investigated at the sequence level in 127 clinical isolates obtained from patients with early Lyme borreliosis evaluated in suburban New York City. Sixteen distinct rrs-rrlA and 16 distinct ospC alleles were identified, representing virtually all of the genotypes previously found in questing Ixodes scapularis nymphs in this region. In addition, a new ospC group was identified in a single patient. The strong linkage observed between the chromosome-located rrs-rrlA and plasmid-borne ospC genes suggests a clonal structure of B. burgdorferi in these isolates, despite evidence of recombination at ospC.

FIG. 1.

Unrooted maximum-likelihood phylogenetic tree based on rrs-rrlA data set and GenBank reference strains. Nonparametric bootstrap values for nodes with >70% support in both maximum-likelihood and maximum-parsimony analyses are above and below the branches, respectively. B. burgdorferi RSP alleles identified in this study are in bold.

FIG. 2.

Unrooted maximum-likelihood phylogenetic tree based on ospC data set and GenBank reference strains. Nonparametric bootstrap values for nodes with >70% support in both maximum-likelihood and maximum-parsimony analyses are above and below the branches, respectively. B. burgdorferi ospC alleles used in this study are in bold.

FIG. 3.

Unrooted maximum-likelihood phylogenetic trees based on rrs-rrlA and ospC alleles. Nonparametric bootstrap values for nodes with >70% support in both maximum-likelihood and maximum-parsimony analyses are above and below the branches, respectively. The arrow indicates the differences between the maximum-likelihood and maximum-parsimony tree topologies supported by bootstrap values of >70% in either a maximum-likelihood or a maximum-parsimony analysis.

FIG. 4.

Alignment of polymorphic nucleotide sites at third codon positions from ospC alleles involved in the putative recombination events. Three possible recombination events are shown. For each panel, the middle sequence represents a putative daughter sequence (the recombinant). The top and bottom sequences represent putative parental sequences. A dot indicates nucleotide identity with the putative daughter sequence. Underlining indicates putative recombination breakpoints identified by at least two recombination methods at P < 0.001.