Evaluation of agents for use in medium for selective isolation of lyme disease and relapsing feverBorrelia species

Barbour-Stoenner-Kelly (BSK) II medium containing fosfomycin, 5-fluorouracil, trimethoprim and sulfamethoxazole was evaluated for the selective isolation of theBorrelia species responsible for Lyme disease and relapsing fever. The maximum noninhibitory concentrations of fosfomycin, 5-fluorouracil, trimethoprim and sulfamethoxazole for six strains of borreliae were 500 to >1000 µg/ml, 250 to >500 µg/ml, 125 to 500 µg/ml and 125 to 500 µg/ml, respectively. The combination of four agents (fosfomycin 400 µg/ml, 5-fluorouracil 100 µg/ml, trimethoprim 10 µg/ml, sulfamethoxazole 50 µg/ml) did not inhibit the growth of borreliae, allowing growth in cultures inoculated with a few organisms (theoretically a single organism). In contrast, the fouragent combination completely inhibited the growth of 12 of 13 other bacterial strains tested as possible contaminants. This combination also allowed the selective growth of borreliae in experimentally contaminated specimens. The four-agent combination in BSK II medium may be useful for selective isolation ofBorrelia species responsible for Lyme disease and relapsing fever from clinical and environmental samples.