Hospital Environments Harbor Chlorhexidine-Tolerant Bacteria Potentially Linked to Chlorhexidine Persistence in the Environment

An integrated approach is essential in combating antibiotic
and
antimicrobial resistance. Chlorhexidine digluconate (CHG), a widely
used antiseptic in medical intensive care units (MICU), has recently
come under scrutiny. However, studies of 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 μg/mL),
including opportunistic pathogens (e.g., Pseudomonas
aeruginosa, Stenotrophomonas maltophilia, Elizabethkingia miricola), with
minimum inhibitory concentrations up to 512 μg/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 chlorhexidine’s efficacy and inform infection prevention
strategies. We advocate for integrated environmental management and
clinical interventions.