Culture-independent detection of chlorhexidine resistance genes qacA/B and smr in bacterial DNA recovered from body sites treated with chlorhexidine-containing dressings

Purpose. Dressings containing chlorhexidine gluconate (CHG) are increasingly used in clinical environments for prevention of infection at central venous catheter insertion sites. Increased tolerance to this biocide in staphylococci is primarily associated with the presence of qacA/B and smr genes. Methodology. We used a culture-independent method to assess the prevalence of these genes in 78 DNA specimens recovered from the skin of 43 patients at catheter insertion sites in the arm that were covered with CHG dressings. Results. Of the 78 DNA specimens analysed, 52 (67 %) possessed qacA/B and 14 (18 %) possessed smr; all samples positive for smr were also positive for qacA/B. These prevalence rates were not statistically greater than those observed in a subsample of specimens taken from non-CHG treated contralateral arms and non-CHG-dressing exposed arms. A statistically greater proportion of specimens with greater than 72 h exposure to CHG dressings were qac-positive (P=0.04), suggesting that the patients were contaminated with bacteria or DNA containing qacA/B during their hospital stay. The presence of qac genes was not positively associated with the presence of DNA specific for Staphylococcus epidermidis and Staphylococcus aureus in these specimens. Conclusion. Our results show that CHG genes are highly prevalent on hospital patients’ skin, even in the absence of viable bacteria.