Dialysis culture for determination of MIC and MBC of benzylpenicillin against Borrelia burgdorferi

Minimal inhibitory concentration (MIC) of benzylpenicillin (Pen G) against strains of Borrelia burgdorferi has earlier been determined by a recently d eveloped dialysis culture technique which provides a constant concentration of Pen G. To further investigate this method, both MIC and minimal bacteri cidal concentration (MBC) of Pen G against B. burgdorferi were determined a nd the results were compared with those obtained by other authors using dif ferent methods. The incubation period was 7 days and subcultures for MBC we re observed for a further 2 weeks. The study showed results of MIC and MBC similar to those of broth microdilution, indicating sensitivity, but lower values than the majority of MIC and MBC results reported by other authors u sing broth macrodilution. It is essential for the results of antibiotic sen sitivity testing in vitro against slowly growing bacteria like Borrelia bur gdorferi that the concentration of antibiotics such as Pen G, which are uns table in solution, is constant during the incubation period.