Clinical characteristics, tolerance mechanisms, and molecular epidemiology of reduced susceptibility to chlorhexidine among Pseudomonas aeruginosa isolated from a teaching hospital in China

•Thirty-two chlorhexidine-tolerant isolates were detected from a total of 294 P. aeruginosa isolates collected from one of the largest comprehensive hospitals in China, accounting for a high rate of 10.9%.•Clinical data showed that reduced susceptibility to chlorhexidine was related to following factors: hospital length of stay, intensive care unit (ICU) admission, length of stay in ICU, invasive procedure, duration of mechanical ventilation, chlorhexidine usage, and occurrence of nosocomial pneumonia.•The hyperexpression of Mex-Opr efflux pump system was the main mechanism that lead to chlorhexidine tolerance.•Chlorhexidine usage or long-term exposure of P. aeruginosa to chlorhexidine could lead to the MDR or cross-resistance phenotypes of antimicrobial drugs.•Our study comprehensively investigates the development and molecular mechanisms of chlorhexidine-tolerant P. aeruginosa, which revealing that we should be aware of surveilling the chlorhexidine tolerance among P. aeruginosa and avoiding the continuous or unreasonable application of chlorhexidine in the hospital settings.