The Two-Component System ChtRS Contributes to Chlorhexidine Tolerance in Enterococcus faecium

is one of the primary causes of nosocomial infections. Disinfectants are commonly used to prevent infections with multidrug-resistant in hospitals. Worryingly, strains that exhibit tolerance to disinfectants have already been described. We aimed to identify and characterize genes that contribute to tolerance to the disinfectant chlorhexidine (CHX). We used a transposon mutant library, constructed in a multidrug-resistant bloodstream isolate, to perform a genome-wide screen to identify genetic determinants involved in tolerance to CHX. We identified a putative two-component system (2CS), composed of a putative sensor histidine kinase (ChtS) and a cognate DNA-binding response regulator (ChtR), which contributed to CHX tolerance in Targeted and deletion mutants exhibited compromised growth in the presence of CHX. Growth of the and mutants was also affected in the presence of the antibiotic bacitracin. The CHX- and bacitracin-tolerant phenotype of E1162 was linked to a unique, nonsynonymous single nucleotide polymorphism in Transmission electron microscopy showed that upon challenge with CHX, the Δ and Δ mutants failed to divide properly and formed long chains. Normal growth and cell morphology were restored when the mutations were complemented in Morphological abnormalities were also observed upon exposure of the Δ and Δ mutants to bacitracin. The tolerance to both chlorhexidine and bacitracin provided by ChtRS in highlights the overlap between responses to disinfectants and antibiotics and the potential for the development of cross-tolerance for these classes of antimicrobials.