Disease severity in a murine model of lyme borreliosis is associated with the genotype of the infecting Borrelia burgdorferi sensu stricto strain

Abstract

The pathogenicity of Borrelia burgdorferi sensu stricto clinical isolates representing 2 distinct ribosomal DNA spacer restriction fragment-length polymorphism genotypes (RSTs) was assessed in a murine model of Lyme disease. B. burgdorferi was recovered from 71.5% and 26.6% of specimens from mice infected with RST1 and RST3 isolates, respectively (P<.0001). The average ankle diameter and histologic scores for carditis and arthritis were significantly higher after 2 weeks of infection among mice infected with RST1 isolates than among those infected with RST3 isolates (P<.001). These clinical manifestations were associated with larger numbers of spirochetes in target tissues but not with the serum sensitivity of the individual isolates. Thus, the development and severity of disease in genetically identical susceptible hosts is determined mainly by the pathogenic properties of the infecting B. burgdorferi isolate. The RST1 genotype is genetically homogeneous and thus may represent a recently evolved clonal lineage that is highly pathogenic in humans and animals.

Figure 1

Measurement of ankle joints of mice infected with distinct rDNA spacer restriction fragment–length polymorphism genotypes (RSTs) of Borrelia burgdorferi. Data are average of results for mice infected with 5 RST1 isolates (n = 25), 2 RST3A isolates (n = 10), or 3 RST3B isolates (n = 15) and the control group (n = 15). P values are comparisons with the control group (2-tailed Student's t test).

Figure 2

Cardiac and joint histopathologic analysis in mice infected with different genotypes of Borrelia burgdorferi. See Materials and Methods for a description of the scoring system. *Histologic data for these isolates were from a previous study [9].

Figure 3

Detection of Borrelia burgdorferi–specific antibodies by Western blotting. Serum or plasma specimens were collected from individual mice 3 weeks after infection. Three representative immunoblot strips for mice infected with each isolate are shown. Identities of major bands on blots are indicated at left. A different lot of strips was used for isolates B491 and B515, which resulted in minor shift in molecular mass of certain bands on blot. +, Positive; −, negative.

Figure 4

Quantification of spirochetes in plasma and tissue samples of C3H/HeJ mice infected with distinct genotypes of Borrelia burgdorferi. All specimens that contained no detectable B. burgdorferi DNA were assigned a value of 1 for comparison. *P < .05 and **P < .001, vs. mice infected with RST3A isolates (Student's t test). Significant differences in the mean no. of spirochetes were also found in skin biopsy (P = .04), joint (P = .02), and heart tissues (P = .002) between mice infected with RST1 and RST3B isolates.

Figure 5

Phylogenetic tree based on 16S–23S rDNA spacer sequences of Borrelia burgdorferi. Tree was constructed by the neighbor-joining method with the MEGA program [25]. Bar, 0.5% divergence. Nos. at branch nodes are the results from bootstrap analysis. B. burgdorferi isolates used in the present study are shown in bold.

Figure 6

Phylogenetic tree based on ospC sequences of Borrelia burgdorferi sensu stricto. Tree was constructed by the neighbor-joining method with the MEGA program [25]. Bar, 2% divergence. Nos. at branch nodes are the results from bootstrap analysis. B. burgdorferi isolates used in this study are shown in bold. B. burgdorferi ospC (OC) alleles and their major OspC groups were defined by Seinost et al. [26]; 4 OspC groups that could cause invasive infection in humans (groups A, B, I, and K) are underlined.