Effect of Benzalkonium Chloride and Chlorhexidine on the Antibiotic Susceptibility of Pseudomonas aeruginosa

Introduction: The transmission of Pseudomonas aeruginosa can be controlled using biocides such as benzalkonium chloride (BKC) and chlorhexidine (CHX). However, debates continue over whether biocide exposure contributes to the development of antibiotic resistance. Objectives: To investigate the impact of BKC and CHX exposure on the development of antibiotic resistance in P. aeruginosa. Methods: The minimal inhibitory concentrations (MICs) of P. aeruginosa PAO1 (ATCC27853) and 15 clinical isolates against BKC and CHX were determined. The bacteria were grown in media containing subinhibitory concentrations (SICs) of these biocides for five consecutive passages. MICs for ciprofloxacin, ceftazidime, and gentamicin, as well as their susceptibility status, were compared before and after exposure. Results: The MIC of BKC ranged from 0.002% to 0.047%, while the MIC of CHX was 0.001%, both well below their recommended concentrations. After exposure to BKC and CHX, most strains showed minimal or no changes in MIC values for ciprofloxacin, ceftazidime, and gentamicin, with no significant changes in antibiotic susceptibility. A few strains, such as SP275, P330, SP119, SP546, and SP48, exhibited more than twofold MIC increases, but these changes were not statistically significant. After CHX exposure, strain P10 showed significant MIC changes without altering its susceptibility status to ciprofloxacin or ceftazidime. Conclusion: Exposure to SICs of BKC and CHX increased antibiotic MICs in a minority of P. aeruginosa strains without affecting their antibiotic susceptibility status. This research provides valuable data supporting the use of biocides in infection control in both healthcare settings and the general environment.