Antimicrob Agents Chemother 2001 Apr;45(4):1292-4

Combination Effect of Vancomycin and beta-Lactams against a Staphylococcus aureus Strain, Mu3, with Heterogeneous Resistance to Vancomycin.

Aritaka N, Hanaki H, Cui L, Hiramatsu K.

Department of Bacteriology, Juntendo University, Tokyo, Japan.

We tested the combined activity of vancomycin and seven beta-lactam antibiotics against Staphylococcus aureus clinical strain Mu3, which displays heterogeneous resistance to vancomycin. When combined with vancomycin, four of the seven tested beta-lactams exhibited an additive effect at or near their MICs, while all showed an antagonistic effect at lower, sub-MIC levels. This study implicated the unpredictable nature of combination therapy of beta-lactams and vancomycin against S. aureus with reduced susceptibility to vancomycin.