In vitro synergy between cefepime and vancomycin against methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis

The in vitro activity of cefepime combined with vancomycin was assessed by the chequerboard method against 35 clinical isolates of methicillin-susceptible (MSSA, n = 8) or -resistant (MRSA, n = 10) Staphylococcus aureus and methicillin-susceptible (MSSE, n = 9) or -resistant (MRSE, n = 8) Staphylococcus epidermidis and S. aureus ATCC 25923 (MSSA). The combination was synergic against 16 isolates and additive/indifferent against 20. For 10 of the clinical isolates (two MSSA, three MESA, two MSSE, three MRSE) and the reference strain, the interaction of cefepime and vancomycin was also determined by the time-kill method. Except for one MESA isolate, synergic killing was demonstrated with clinically achievable concentrations of vancomycin (0.5-1 mg/L) and cefepime (methicillin-susceptible isolates: 0.5-1 mg/L; methicillin-resistant isolates: 2-64 mg/L).