Seventy-one isolates of Borrelia burgdorferi sensu lato (B.b.s.l.) derived from Ixodes ricinus ticks (50 strains) and patients (21 strains) were characterised by PCR-RLFP analysis. In four cases the human isolates were obtained from the cerebrospinal fluid (CSF) of patients with clinical symptoms of neuroborreliosis and in 17 cases from skin biopsies of patients with dermatological manifestation of
Lyme borreliosis. Ixodes ricinus isolates originated from 14 localities in three regions (Mur valley, eastern and western Styria) in Styria. Thirty six strains of B.b.s.l. were isolated from nymphal ticks, nine strains from female and five strains from male ticks. Species identification of human isolates revealed three B. garinii and one B. afzelii isolates in CSF. In the PCR-RFLP analysis of 17 skin specimens a pattern for B. afzelii was found in ten cases, while six could be identified as B. garinii and one as a mixed infection of B. afzelii and B. garinii. Genetic characterisation of tick isolates resulted in 24 strains of B. afzelii (48%), 11 strains of B. garinii (40%) and 5 strains of B. burgdorferi s.st. (10%); one isolate showed a mixed infection of B. afzelii and B. garinii. Our findings indicate that B. afzelii and B. garinii predominate over B. burgdorferi s.str. in Ixodes ricinus ticks from Styria, which is similar to findings in neighbouring countries. This also reflects the occurrence of different pathogenic Borrelia strains in human samples.