Heteroresistance to Vancomycin in Enterococcus faecium

This study presents the first report of vancomycin heteroresistance in an Enterococcus faecium isolate from a patient. The original isolate was susceptible in vitro to vancomycin. E-tests showed growth of subcolonies in a zone of inhibition with a vancomycin MIC of >256 μg/ml. Both the susceptible and resistant colonies were from the same strain as determined by PFGE, and both contained the vanA gene as determined by PCR.