Enterococcus faecium and Ampicillin Susceptibility Determination: Overestimation of Resistance with Disk Diffusion Method Using 2 Micrograms of Ampicillin?

We would like to focus your attention on ampicillin susceptibility testing for Enterococcus faecium infections. Ampicillin resistance in E. faecium is due to two distinct mechanisms: low-level resistance based on increased quantity of penicillin binding protein 5 (PBP5), which has low affinity for