Increasing tolerance of hospital Enterococcus faecium to hand-wash alcohols

Alcohol-based hand rubs are international pillars of hospital infection control, restricting transmission of pathogens such as Staphylococcus aureus. Despite this success, health care infections caused by Enterococcus faecium (Efm) - another multidrug resistant pathogen - are increasing. We tested alcohol tolerance of 139 hospital Efm isolates, obtained between 1997 and 2015 and found Efm post-2010 were 10-fold more tolerant to alcohol killing than older isolates. Using a mouse infection control model, we then showed that alcohol tolerant Efm resisted standard 70% isopropanol surface disinfection and led to gastrointestinal colonization significantly more often than alcohol sensitive Efm. We next looked for bacterial genomic signatures of adaptation. Tolerant Efm have independently accumulated mutations modifying genes involved in carbohydrate uptake and metabolism. Mutagenesis confirmed their roles in isopropanol tolerance. These findings suggest bacterial adaptation and complicate infection control recommendations. Additional policies and procedures to prevent Efm spread are required.