Exploring the Role of Piperacillin and Tazobactam in Combination with Vancomycin against Methicillin-Resistant Staphylococcus aureus

Previous studies have demonstrated synergy between piperacillin (PIP)-tazobactam (TAZ) (TZP) and vancomycin (VAN) against methicillin-resistant Staphylococcus aureus (MRSA). However, it is unknown whether PIP and/or TAZ synergizes with VAN against MRSA. We sought to determine whether PIP and/or TAZ synergizes with VAN against MRSA in vitro. The activity of PIP and/or TAZ with and without VAN (1/2 the minimum inhibitory concentration) was tested against 5 clinical MRSA isolates using a 24-h time-kill methodology. Antibiotic susceptibilities, accessory gene regulator (agr) operon functionality, and US strain type were also determined for the isolates. The combination of VAN and TZP was bactericidal against 3/5 isolates and synergistic against 4/5 isolates tested. Neither PIP nor TAZ alone combined with VAN demonstrated a significant reduction in bacterial growth. The combination of TZP and VAN was less active against the lone isolate with agr dysfunction. In summation, the combination of VAN with both PIP and TAZ was required for synergy against MRSA. This antibiotic combination may not be effective against unique MRSA strain types.