Chlorhexidine driven Colistin resistance
A group of researchers at Public Health England’s laboratories at Porton Down have released a somewhat disturbing study showing that exposure of Klebsiella pneumonia to chlorhexidine can be linked to increased resistance to colistin – one of the “antibiotics of last resort”.
Published in Antimicrobial Agents & Chemotherapy, the team led by Dr Mark Sutton, exposed clinical strains of Klebsiella pneumonia to sub-lethal concentrations of chlorhexidine and slowly doubled the exposure concentration over a number a growth experiments or passages. This artificially selected K.pneumonia organisms that were resistant to chlorhexidine. These chlorhexidine resistant strains were exposed to colistin along with their non-chlorhexidine resistant wild type strains. The researchers found that the minimum inhibitory concentration (MIC) of colistin for the wild type strains was 2-4 mg/L, whereas the chlorhexidine resistant / adapted strains had colistin MICs of >64 mg/L. This has serious implications for healthcare facilities, as chlorhexidine is a commonly used antimicrobial agent, with in use concentrations varying from 0.02% in catheter maintenance solutions, up to 4% in antimicrobial wound dressings. These large variations in chlorhexidine concentration make the likelihood of micro-organism adaptation and selection for chlorhexidine resistance much higher. Consequently, the probability of micro-organism developing colistin resistance (in the case Klebsiella pneumonia) is also increased.
Interestingly, the researchers reversed the experiment, carrying out an artificial selection for Klebsiella pneumonia strains resistant to colistin. They then exposed those colistin resistant strains to various concentrations of chlorhexidine to determine whether the development of colistin resistance could drive development of chlorhexidine resistance – it did not.
This study is concerning, particularly as for multi-drug resistant strains of carbapenemase producing Klebsiella pneumonia, colistin is one of the few remaining effective antibiotics. Use of chlorhexidine is widespread and its potential to drive colistin resistance should be carefully reviewed and considered by infection control teams. Bioquell’s hydrogen peroxide vapour decontamination technology is effective against all strains of Klebsiella pneumonia and can be an important tool to aid in the control of multi-drug resistant outbreaks.