Evaluation of the in vitro activities of ceftobiprole and comparators in staphylococcal colony or microtitre plate biofilm assays

The aim of this study was to evaluate the in vitro efficacy of ceftobiprole and comparator antibiotics, either alone or in combination, in staphylococcal MBECTM (minimum biofilm eradication concentration) and colony biofilm assays at dilutions of the maximum free-drug plasma concentration attained during clinical use (fC(max)). Staphylococci tested included meticillin-susceptible and meticillin-resistant Staphylococcus aureus (n = 6) and Staphylococcus epidermidis (n = 2). Relative to no-drug controls, after 7 days of exposure ceftobiprole concentrations from 1/4 fC(max) to fC(max) generally decreased CFUs in MBEC or colony biofilms of S. aureus isolates by ca. 1.5 log(10) to >= 2.5 log(10). Gentamicin reduced colony biofilm CFUs by >= 1.4 log(10) at these concentrations with gentamicin-susceptible isolates. Following 7 days of exposure, vancomycin and rifampicin were ineffective as single agents or in combination in the colony model, but yielded CFU decreases from 0 to 5 log(10) in the MBEC model. Treatment of biofilms with rifampicin for 7 days yielded rifampicin-resistant mutants, and the selection of rifampicin resistance was inhibited by co-treatment with ceftobiprole. Thus, ceftobiprole alone or in combination demonstrated promising activity against biofilms of meticillin-susceptible and - resistant staphylococci at clinically relevant concentrations. In contrast, vancomycin and rifampicin, two agents used clinically for the treatment of biofilm infections, tested separately or together gave inconsistent results and generally had little impact on cell viability. (C) 2013 Elsevier B. V. and the International Society of Chemotherapy. All rights reserved.