High Prevalence of Antiseptic Resistance Encoding Genes and Reduced Phenotypic Antiseptic Susceptibility Among Antibiotic-Resistant Pseudomonas aeruginosa Isolates

Background: Multi-drug resistant (MDR) and extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates are of clinical concern. Objectives: To determine the distribution of antiseptic resistance genes and the associated level of phenotypic antiseptic resistance against quaternary ammonium compounds and biguanide compounds, we studied MDR and XDR P. aeruginosa isolates collected from different infections among patients from a single hospital. Methods: Pseudomonas aeruginosa isolates were investigated in 2020 for in vitro susceptibility to benzethonium chloride (BTC), benzalkonium chloride (BKC), and chlorhexidine digluconate (CHG). The minimum inhibitory concentrations (MICs) against these antiseptic agents were determined using broth microdilution. Also, polymerase chain reaction (PCR)-mediated detection of qacE, qacEΔ1, and blaOXA-23 genes was used. Results: Isolates were largely non-clonal according to their phenotypical and genotypical non-similarity (35 overall data-combination types detected). Most P. aeruginosa infections occurred in intensive care unit (ICU) patients (n = 43, 61.4%). Extensively drug-resistant and MDR phenotypes were detected in 20% and 12.6%, respectively. Among the 70 isolates retained, 53 (75.7%) harbored at least one resistance gene, comprising 11 (20.7%) isolates with solely the qacEΔ1 gene; seven (13.2%) isolates harbored the qacE gene. Both the qacE and qacEΔ1 genes were detected simultaneously in 35 (66%) isolates. The mean MICs for BTC (24.0 versus 10.56 µg/mL), BKC (46.1 versus 17.22 µg/mL), and CHG (107.7 versus 29.4 µg/mL) were statistically significantly higher among antiseptic resistance gene harboring isolates than in other isolates without such genes. Conclusions: The significantly increased MICs against antiseptic agents among antibiotic-resistant P. aeruginosa isolates highlight the importance of monitoring such increases and implementing effective infection control.