Chlorhexidine exposure of clinical Klebsiella pneumoniae strains leads to acquired resistance to this disinfectant and to colistin

Abstract Chlorhexidine is widely employed as a disinfectant in hospitals, which may have imposed a selective pressure on bacteria. This study aimed to determine whether continuous exposure to chlorhexidine could lead to adaptive resistance and cross-resistance, and furthermore investigated the potential resistance mechanisms. Three Klebsiella pneumoniae clinical strains susceptible to conventional antimicrobials were selected and continuously cultured in broth with gradually increasing concentrations of chlorhexidine. Antimicrobial susceptibility was determined. Mechanisms of acquired resistance to chlorhexidine and colistin were analyzed by PCR and quantitative RT-PCR. Furthermore, fitness was assessed through growth curve assays. Increased resistance to chlorhexidine and colistin was found in all strains. Expressions of the cepA gene were upregulated in the adapted strains, suggesting that hyper-expression of cepA was probably the main mechanism of adaptive resistance to chlorhexidine. The amino acid substitutions Leu82Arg and Arg256Gly in PmrB were detected in all of the adapted strains, while Leu344Pro was only identified in one adapted strain, indicating that the PmrB substitution was responsible for the cross-resistance phenotype. Moreover, chlorhexidine adaptation might have an effect on bacterial growth.