Nosocomial Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus: Sensitivity to Chlorhexidine-Based Biocides and Prevalence of Efflux Pump Genes

Abstract

The widespread use of disinfectants and antiseptics has led to the emergence of nosocomial pathogens that are less sensitive to these agents, which in combination with multidrug resistance (MDR) can pose a significant epidemiologic risk. We investigated the susceptibility of nosocomial <i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>, <i>Pseudomonas aeruginosa</i>, and <i>Staphylococcus aureus</i> to a 0.05% chlorhexidine (CHX) solution and a biocidal S7 composite solution based on CHX (0.07%) and benzalkonium chloride (BAC, 0.055%). The prevalence of efflux pump genes associated with biocide resistance and their relationship to antibiotic resistance was also determined. Both biocides were more effective against Gram-positive <i>S. aureus</i> than Gram-negative bacteria. The most resistant strains were <i>P. aeruginosa</i> strains, which were mainly killed by 0.0016% CHX and by 0.0000084% (CHX)/0.0000066% (BAC) S7. The S7 bactericidal effect was observed on <i>P. aeruginosa</i> and <i>S. aureus</i> after 10 min, while the bactericidal effect of CHX was only observed after 30 min. <i>qacEΔ1</i> and <i>qacE</i> efflux pump genes were prevalent among <i>E. coli</i> and <i>K. pneumoniae</i>, while <i>mexB</i> was more often detected in <i>P. aeruginosa</i>. <i>norA</i>, <i>norB</i>, <i>mepA</i>, <i>mdeA</i>, and <i>sepA</i> were prevalent in <i>S. aureus</i>. The observed prevalence of efflux pump genes highlights the potential problem whereby the sensitivity of bacteria to biocides could decline rapidly in the future.