Increasing tolerance of hospital <i>Enterococcus faecium</i> to handwash alcohols

Alcohol-based disinfectants and particularly hand rubs are a key way to control hospital infections worldwide. Such disinfectants restrict transmission of pathogens, such as multidrug-resistant <i>Staphylococcus aureus</i> and <i>Enterococcus faecium</i> Despite this success, health care infections caused by <i>E. faecium</i> are increasing. We tested alcohol tolerance of 139 hospital isolates of <i>E. faecium</i> obtained between 1997 and 2015 and found that <i>E. faecium</i> isolates after 2010 were 10-fold more tolerant to killing by alcohol than were older isolates. Using a mouse gut colonization model of <i>E. faecium</i> transmission, we showed that alcohol-tolerant <i>E. faecium</i> resisted standard 70% isopropanol surface disinfection, resulting in greater mouse gut colonization compared to alcohol-sensitive <i>E. faecium</i> We next looked for bacterial genomic signatures of adaptation. Alcohol-tolerant <i>E. faecium</i> accumulated mutations in genes involved in carbohydrate uptake and metabolism. Mutagenesis confirmed the roles of these genes in the tolerance of <i>E. faecium</i> to isopropanol. These findings suggest that bacterial adaptation is complicating infection control recommendations, necessitating additional procedures to prevent <i>E. faecium</i> from spreading in hospital settings.