Prevalence of chlorhexidine tolerance genes amongst coagulase negative staphylococci recovered from catheters and catheter associated skin sites

Gram-positive coagulase-negative staphylococci (CNS) are a major cause of catheter related infections, including catheter related bloodstream infections. These bacteria are found on the skin of patients as part of the normal microflora. As a consequence, antiseptics such as chlorhexidine gluconate (CHG) are employed in hospitals for the bacterial decolonisation of skin before clinical procedures, including at catheter insertion sites. Increased tolerance to CHG has been observed in multiple studies and is associated with the acquisition and expression of qac genes in staphylococci. Here we assessed changes in CHG tolerance and the presence of qac genes in 90 CNS isolates, including S. epidermidis (n= 37) and S. capitis (n=40), recovered from the catheters or skin at catheter insertion sites. Forty-five percent of all isolates possessed qacA/B and/or smr. Thirty eight percent also showed an increased tolerance to CHG (≥4mg/L). While there was a statistically significant association between possession of qac/smr and increased CHG tolerance in S. epidermidis, this was not the case for S. capitis. Furthermore qac-positive strains were able to tolerate CHG at higher concentrations than qac-negative strains during biofilm growth. Within the isolates, methicillin resistance was observed in 81% of S. epidermidis and 70% of S. capitis isolates. Gentamicin resistance was observed in 48.6% and 42.5% of isolates of these species. There was no statistical association between the presences of qac genes and antibiotic resistance in this study.