Selected phenotypic features of BR91, a unique spirochaetal strain isolated from the Culex pipiens mosquito

Growth temperature range, resistance to selective antibiotics, activities of 23 enzymes, protein fingerprints and fatty acids composition of the spirochaetal strain BR91, isolated from the Culex pipiens mosquito, were tested. The spirochaetes were grown in BSK-H Complete liquid medium. The optimal in vitro growth temperature of the strain was 33 °C. Strain BR91 was sensitive to trimethoprim, nalidixic acid, 5-fluorouracil, and tolerated phosphomycin. The strain produced acid and alkaline phosphatase, esterase (C4), esterase-lipase (C8), leucine arylamidase, naphthol-AS-BI-phosphohydrolase and α-fucosidase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) assay revealed several major proteins in the size range of 13-16 kDa, 22-30 kDa and 37-131 kDa. Fatty acid methyl ester (FAME) analysis showed that C₁₄:₀, C₁₆:₀, C₁₈:₁ ω9c and summed feature 5 (C₁₈:₂ ω6,9c and/or C₁₈:₀ anteiso) are major fatty acids. This study highlights certain phenotypic differences between strain BR91 and the Lyme disease spirochaete Borrelia burgdorferi, and supports the hypothesis that strain BR91 represents a unique taxonomical entity in a system of spirochaetal species.