Characterisation of Borrelia burgdorferi sensu lato strains isolated from patients with skin manifestations of Lyme borreliosis residing in Slovenia

Lyme borreliosis is the most prevalent tick-borne infection in Slovenia. Skin disorders are the most frequent clinical manifestations. The aim of the present study was to assess the phenotypic and genotypic diversity of a large number of human Borrelia burgdorferi sensu lato isolates and to evaluate any association between the isolates and different clinical manifestations. All 103 strains tested were from patients suffering from the skin disorders of Lyme borreliosis. Skin biopsies, cerebrospinal fluid and blood samples from patients were inoculated into modified Kelly Pettenkofer medium. Protein profiles were determined by SDS-PAGE and species identification and plasmid profiles by pulsed-field gel electrophoresis. MluI digestion profiles showed that 87 (84.5%) isolates belonged to B. afzelii, 15 (14.5%) to B. garinii and 1 (1%) to B. burgdorferi sensu stricto. The number of plasmids in each strain varied from three to seven, and the plasmid size ranged from 15 to 65 kb. Four isolates of B. garinii possessed multiple large plasmids and four isolates had a large plasmid dimer (three B. afzelii and one B. garinii). Isolates showed qualitative and quantitative differences in protein expression. The study found differences in the expression of OspB and OspC proteins between B. afzelii and B. garinii strains. OspB was expressed significantly more often by B. afzelii (78 of 87, 89.6%) than by B. garinii (4 of 15, 26.6%) isolates, while OspC protein was expressed significantly more often by B. garinii (14 of 15, 93.3%) than by B. afzelii (51 of 87, 58.6%) isolates. In Slovenia, B. afzelii causes the majority of skin lesions. The isolates investigated showed plasmid and protein diversity. Heterogeneity of the spirochaetes may be important for virulence, and may have implications for pathogenesis and therapy of the infection. Differences in immunodominant proteins also have an important impact on serological testing and vaccine development.