Identification of 2CS-CHX operon signature of chlorhexidine tolerance among .

Chlorhexidine (CHX) is a broad-spectrum antiseptic widely used in community and clinical contexts for many years, recently acquiring higher relevance in nosocomial infections control worldwide. Despite of this, CHX tolerance has been poorly understood among , one of the leading agents causing nosocomial infections. This study provides new phenotypic and molecular data for a better identification of CHX tolerant subpopulations in community and clinical contexts. MIC distribution of 106 suggested the occurrence of tolerant subpopulations in diverse sources (human, animal, food, environment) and phylogenomic backgrounds (clades A1/A2/B), with predominance in clade A1. They carried a specific variant of 2CS-CHX operon, here identified. It encodes a glucose and an amino-acid-polyamine-organocation family transporters, besides the DNA-binding-response-regulator ChtR with a P102H mutation previously described in only CHX tolerant clade A1 and the ChtS sensor. 2CS-CHX seems to be associated with three regulons modulating diverse bacteria biological functions. Combined data from normal MIC distribution and 2CS-CHX operon characterization supports a tentative epidemiological cut-off (ECOFF) of 8 mg/L to CHX, useful to detect tolerant populations in future surveillance studies. The spread of tolerant in diverse epidemiological backgrounds alerts for a prudent use of CHX in multiple contexts.: Chlorhexidine is one of the substances included in the World Health Organization's List of Essential Medicines which comprises the safest and most effective medicines needed in global health systems. Although it has been widely applied as a disinfectant and antiseptic since the 1950s in healthcare (skin, hands, mouthwashes, eye drops), its use in hospitals to prevent nosocomial infections has increased worldwide in recent years. Here we provide a comprehensive study on chlorhexidine tolerance among , one of the leading nosocomial agents worldwide, and identified a novel 2CS-CHX operon as a signature of tolerant strains occurring in diverse phylogenomic groups. Our data allowed to propose a tentative epidemiological cut-off of 8 mg/L, useful to detect tolerant populations in future surveillance studies in community and clinical contexts. The prediction of 2CS-CHX regulons will also facilitate the design of future experimental studies to better uncover chlorhexidine tolerance among .