Hospital environments harbor chlorhexidine tolerant bacteria potentially linked to chlorhexidine persistence in the environment

A One Health approach is essential in combating antibiotic and antimicrobial resistance. Chlorhexidine (di)gluconate (CHG), a widely used antiseptic in medical intensive care units (MICU), has recently come under scrutiny. However, studies on CHG tolerance, particularly in interconnected indoor environments, are limited. We comprehensively explored CHG tolerance in MICU environments from chemical, microbial, and molecular perspectives. Using microcosm experiments and field surveys, we demonstrated that CHG, if transferred from patient skin to environments, can persist on surfaces despite cleaning and disinfection and decrease to sublethal levels for clinically relevant bacteria. We detected widespread CHG-tolerant bacteria ([≥] 18.75 {micro}g/mL), including opportunistic pathogens (e.g., Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Elizabethkingia miricola), with minimum inhibitory concentrations up to 512 g/mL. Sink drains emerged as critical hotspots, and indoor air as a potential transport mechanism. We observed indications of bacterial persistence, increased tolerance, in-situ evolution, and dissemination across MICU rooms. Molecular analyses revealed heterogeneous and largely unexplored CHG resistance mechanisms and identified resistance determinant candidates, particularly qacEdelta1-carrying, plasmid-borne multidrug-resistant cassettes. Our findings underscore the importance of understanding human-environment and chemical-microbe interactions to preserve chlorhexidines efficacy and inform infection prevention strategies. We advocate for integrated environmental management and clinical interventions under the One Health framework.