The evolution of alcohol-tolerant strains of Enterococcus faecium could possibly undermine the effectiveness of alcohol-based disinfectant standard precautions, new data suggest.
"Extension of active surveillance cultures outside high-risk areas of the hospital and return to strict contact precautions during outbreaks with new emergent strains of [vancomycin-resistant enterococci] may be required to prevent widespread cross-contamination," senior author Timothy P. Stinear, PhD, professor of microbiology and immunology at the University of Melbourne in Australia, told Medscape Medical News.
The findings echo the results from a previous study, which found that bacteria can develop tolerance to biocides such as chlorhexidine, an active agent that is sometimes added to alcohol-based hand rub products. The new study is thus another reminder that bacteria evolve in response to infection control efforts, thereby complicating infection control recommendations.
Sacha J. Pidot, PhD, postdoctoral researcher, also from the University of Melbourne, and colleagues published their findings online August 1 in Science Translational Medicine. The investigators evaluated 139 isolates of E faecium from two hospitals in Australia. When they analyzed isolates obtained between 1997 and 2015, they found that E faecium isolates obtained after 2010 were 10-fold more tolerant to killing by alcohol than were the older isolates (0.97 log10 mean difference, P < .0001).
The alcohol-tolerant E faecium resisted the 70% isopropanol surface disinfection used in a standard mouse gut colonization model of E faecium transmission. Across four independent experiments, the researchers found that a significantly greater number of mice were colonized by the alcohol-tolerant E faecium isolate then the more susceptible E faecium isolate (P < .01).
Thus, alcohol-tolerant isolates more effectively colonized mice than did the alcohol-sensitive isolates. The findings suggest that it may be necessary to develop additional procedures to prevent the spread of E faecium in hospital settings.
Alcohol-based Sanitizer Controls MRSA
"In 2005, we published a 3-year study describing a progressive decline in rates of hospital acquired methicillin-resistant [Staphylococcus] aureus and Gram-negative infections after the introduction and promotion of alcohol-based hand rubs," the authors write. "Similar programs were progressively rolled out to all major hospitals in Australia, and compliance with the use of alcohol-based hand rubs is now a nationally reportable key performance indicator. The 2015 Australian National Hand Hygiene program report shows high (>80%) compliance rates in health care facilities across the country (www.hha.org.au), and staphylococcal infection rates have declined nationally."
Unfortunately, this effective infection control strategy coincided with a gradual increase in vancomycin-resistant enterococci infections. Although the current study focuses on E faecium, Stinear acknowledged that it is "entirely possible" that similar tolerances may be occurring in other microbes of the gastrointestinal tract.
Implications for Infection Control
The researchers have begun to investigate the mechanism underlying the development of tolerance. "Our phylogenetic convergence and [discriminant analysis of principal components] across distinct E. faecium lineages identified changes in several genetic loci likely contributing to alcohol tolerance," explain the authors. Although their research into the genetics underlying alcohol tolerance is not yet complete, preliminary results point to mutations in loci involved in carbohydrate transport and metabolism.
Stinear advised that, "In hospitals with endemic [vancomycin-resistant enterococci], it would seem prudent to optimize adherence to alcohol-based disinfectant protocols to ensure adequate exposure times and use sufficient volume of product, particularly each time healthcare workers clean their hands."
"Consideration may need to be given to the use of various formulations of alcohol-based hand rubs (eg, foams and gels), since they are known to have variable (generally reduced) efficacy compared to solutions," Stinear added.
The authors have disclosed no relevant financial relationships.
Sci Transl Med. Published online August 1, 2018. Abstract
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