Vancomycin-variable Enterococcus Faecium: in Vivo Emergence of Vancomycin Resistance in a Vancomycin-Susceptible Isolate.

We report the emergence of vancomycin resistance in a patient colonized with a vanA-containing, vanRS-negative isolate of Enterococcus faecium which was initially vancomycin susceptible. This is a previously undescribed mechanism of drug resistance with diagnostic and therapeutic implications.