In vitro activities of faropenem, ertapenem, imipenem and meropenem against Borrelia burgdorferi s.l.

Little is known about the in vitro activity of penems and carbapenems against the spirochete Borrelia burgdorferi. Here, faropenem, ertapenem, imipenem and meropenem as well as the third-generation cephalosporin ceftriaxone and tobramycin were tested in vitro against 11 isolates of the B. burgdorferi sensu lato complex. On a μg/mL basis, ertapenem was the most potent carbapenem (minimal inhibitory concentration (MIC) range: 0.015–0.125 μg/mL), with in vitro activity comparable with that of ceftriaxone against Borrelia. These findings are supported by the results of time–kill experiments in a Borrelia afzelii skin isolate, demonstrating a >3 log10 unit (99.9%) reduction of the inoculum after 96 h of exposure to either drug at a concentration of three log2 unit dilutions above the respective MIC.