Over the past couple of decades the increased use of alcohol-based hand sanitizers and disinfectants in hospitals has been incredibly successful in reducing cases of deadly golden staph infections. However, a new study has found that some bacteria are now becoming resistant to these alcohol-based sanitizers.

The research began when Professor Paul Johnson started to wonder why, when golden staph infections were decreasing, infections in another bacterial pathogen, Enterococcus faecium, were rising. Despite the rapid evolution of antibiotic-resistant superbugs, modern regimented infection controls at many hospitals have helped reduce infections over time. Johnson approached colleague Tim Stinear with the compelling hypothesis that maybe some bacteria was becoming resistant to strong alcohol-based sanitizers.

"Paul said maybe they're becoming tolerant to all the alcohols we use in our hand hygiene products," says Stinear, co-author on the recent study, "and we said, that's ridiculous. What are the chances that something could become tolerant to alcohol? It's a broad-spectrum disinfectant – it gets into the bacterial membranes and blows them apart. It's a general annihilator of cells."

First identified in the 1980s, several strains of enterococcus bacterial genus have generated a resistance to the antibiotic vancomycin. These vancomycin-resistant enterococci (VRE) are becoming an increasing problem in hospitals around the world, and in 2017 the CDC published a paper suggesting the spread of Enterococcus faecium in particular, is reaching critical epidemic levels.

The new research tested 139 different strains of Enterococcus faecium, found in Australian hospitals over a twenty year period. The bacteria was treated with an isopropanol solution, similar to the alcohol used to kill bacteria in common hand sanitizers. Strikingly the researchers found that bacterial strains collected after 2010 were 10 times more tolerant to alcohol solutions than older strains.

"We started testing to see whether they had any tolerance to alcohol, and sure enough, the new isolates were more tolerant to alcohol exposure than the older isolates," says Stinear.

The researchers correlated this increased resistance in the bacteria to the growth in hospital hand sanitizer use. Over the past 15 years Stinear notes that "alcohol use in hospitals has gone from hundreds of liters a month to thousands of liters a month of these alcohol-based disinfectants."

Instead of discrediting the efficacy of alcohol-based hand sanitizers, the study does suggest that many people using these products don't rub their hands together for a thorough enough time to completely eliminate traces of bacteria. The recommended optimal duration is 20 to 30 seconds but as Stinear suggests, "anywhere you have sub-optimal contact times with the full-strength product you're going to risk some breakthrough, or bacteria persisting."

The conclusion of the research is an urgent recommendation that, as well as more stringent cleaning regimes, additional sanitizing procedures be investigated. Extra disinfectants, beyond those alcohol-based ones, will be needed in the future to prevent this dangerous pathogen from spreading.

The new research was published in the journal Science Translational Medicine.