Susceptibility to chlorhexidine amongst multidrug-resistant clinical isolates of Staphylococcus epidermidis from bloodstream infections

Emergence of Staphylococcus isolates with reduced susceptibility to chlorhexidine is being increasingly reported. We present an update to a previous report showing continuing efficacy of chlorhexidine-based infection control measures against Staphylococcus aureus over six years. We screened qacA/B genes in Staphylococcus isolates collected over another six years in the same intensive therapy unit in Scotland where chlorhexidine baths form an essential component of long-term control of nosocomial infections. Consistent with our previous study we report minimal presence of qacA/B in S. aureus strains from screening samples and bacteraemia patients but the new finding of a high proportion of qacA/B carriage in Staphylococcus epidermidis associated to reduced susceptibility to chlorhexidine. S. epidermidis isolates positive for qacA/B were clonally diverse although 65% of isolates belonged to the multidrug resistant clone ST-2. These findings raise concerns in relation to selection of multidrug resistant strains by chlorhexidine and are important in the context of recent evidence emphasising the benefits of targeting bloodstream infections associated with coagulase-negative staphylococci.