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A novel, fast-growing spirochaete was isolated from the hard tick Hyalomma aegyptium (family Ixodidae, subfamily Metastriata) using Barbour-Stoenner-Kelly (BSK) II medium. Tick samples were taken during the summer of 2000 from the Istanbul area in northwestern Turkey. Sixty-seven of 153 adults (44%) and 72 of 185 nymphs (39%) were infected with the novel spirochaete, whereas none of the 20 larvae examined were infected. The optimal growth temperature of the spirochaete in BSK II medium was 34-37 degrees C, and it could grow at 39 degrees C. Doubling times at 34 and 37 degrees C were 5.3 and 5.1 h, respectively. Six pure cultures of the spirochaete were obtained and characterized by microscopic observation, sequence analysis of the flagellin gene (flaB), SDS-PAGE and Western blotting. The spirochaete was morphologically similar to those of the genus Borrelia and contained a 41 kDa protein reactive with mAb H9724 specific to the flagellin of a Borrelia species. Polyclonal antibody raised to this spirochaete reacted with several antigen bands, whereas no bands were detected with Borrelia burgdorferi, Borrelia hermsii, Borrelia turicatae and Borrelia parkeri. The flaB sequences of the six isolates showed high similarity, with sequence similarity values ranging from 99.2 to 100%; however, the similarity of the isolates’ flaB sequences to those of the
Lyme-disease-related Borrelia and relapsing-fever-associated Borrelia species was less than 90%. These findings suggest that the unique spirochaete is a member of the genus Borrelia, and differs from previously described Borrelia species.