Distribution of chlorhexidine resistance genes among Staphylococcus aureus clinical isolates: the challenge of antiseptic resistance.

Introduction: Chlorhexidine is an antiseptic agent which is extensively used to prevent nosocomial infections; however, this could result in reduction of its susceptibility. The aim of this work was to determine chlorhexidine susceptibility among Staphylococcus aureus isolates and to detect qacA/B and smr antiseptic resistance genes among these isolates. Furthermore, we aimed to identify possible risk factors for the reduction of chlorhexidine susceptibility among S. aureus isolates.

Methods: Various clinical samples were collected from patients with evidence of S. aureus infection. Antimicrobial susceptibilities of identified S. aureus isolates were determined by disk diffusion method. Resistance to methicillin was identified by cefoxitin disk diffusion test besides mecA gene detection by PCR. Chlorhexidine minimum inhibitory concentration (MIC) values were measured by broth microdilution method while qacA/B and smr resistance genes were detected by multiplex PCR.

Results: A total percentage of 25.9% of S. aureus isolates showed reduced susceptibility to chlorhexidine. Methicillin resistant S. aureus (MRSA) had a reported percentage of 39.5%, which was significantly higher than the 11.3% reported for methicillin susceptible S. aureus (MSSA), p<0.001. S. aureus isolates were found to harbor qacA/B and smr genes at 23.2% and 7.7% respectively. Risk factors for reduced susceptibility to chlorhexidine included; ICU setting (OR=2.02, 95%CI: 0.3-1.6), prolonged ICU stay (OR=1.7, 95%CI: 0.4-1.1), presence of central vascular catheter (OR=2.3, 95%CI: 0.2-1.9), mechanical ventilation (OR=1.88, 95%CI: 0.4-1.7) and acquisition of qacA/B (OR=15.7, 95%CI: 3.4-12.1) or smr gene (OR=15.7, 95%CI: 3.4-12.1).

Conclusions: Our work highlighted the current challenge of antiseptic resistance in our locality. The frequencies of qacA/B and smr genes were significantly higher among MRSA than MSSA isolates. About two thirds of chlorhexidine tolerant isolates displayed an MDR profile. To maintain chlorhexidine efficiency, biocidal stewardship program and ongoing surveillance are essential.