Lyme borreliosis is the most frequent tick-borne
disease in the Northern hemisphere. Here we describe the first isolation of Borrelia burgdorferi sensu lato in Bulgaria: the midguts of 47 Ixodes ricinus obtained by flagging from the Central park in Sofia, Bulgaria were cultivated for borreliae in BSK medium. The eight isolates obtained from the ticks and one skin isolate from a Bulgarian patient with erythema migrans were subjected to phenotypic [outer surface protein A (OspA) serotyping] and genotypic analysis (pulsed-field gel electrophoresis typing followed by large restriction fragment pattern analysis after MluI digestion, polymerase chain reaction with 16S rRNA-directed oligonucleotide probes, and restriction fragment length polymorphism analysis of rrf-rrl intergenic spacer amplicons). The skin isolate was B. burgdorferi sensu stricto, as were four of the tick isolates; the other four tick isolates were B. garinii representing three different OspA serotypes (types 3, 5 and 7). These findings confirm the wide geographic distribution of the different B. garinii-associated OspA serotypes in Europe (shown here for the first time for the Southeastern part of Europe) and of B. burgdorferi sensu stricto in the Western hemisphere. These findings have implications for development of diagnostic tests and a borrelia vaccine in Southeastern Europe.