Phenotypic chlorhexidine and triclosan susceptibility in clinical Staphylococcus aureus isolates in Australia

Antiseptics such as chlorhexidine gluconate and triclosan are widely used in healthcare settings for both skin antisepsis and decolonisation of Staphylococcus aureus. We determined the minimum inhibitory concentration (MIC) of 198 methicillin susceptible and resistant Staphylococcus aureus clinical isolates to both chlorhexidine and triclosan using an agar dilution method. Of these, 10% (19/198) showed a raised MIC to chlorhexidine and 3% (6/198) showed an elevated MIC to triclosan. The multilocus sequence type (MLST) of each isolate was predicted using a binary method, and although ST93-MRSA-IV was the most common, ST22-MRSA-IV was shown to have statistically higher chlorhexidine MIC values compared with non ST22-MRSA-IV isolates (z = -8.7, p < 0.01). Additionally, isolates from patients known to have failed decolonisation were included and did not demonstrate elevated MIC to the decolonisation antiseptic. Monitoring for non-susceptibility of clinical isolates to biocides is important to determine trends, and may have clinical implications in terms of sub-lethal concentration in residues and concomitant antibiotic resistance.