Hand sanitizers have become important tools in combating the spread of infections, particularly in health care settings; nowadays, you can’t walk far in a hospital or medical clinic without seeing clusters of disinfectant dispensers. But as Maggie Fox reports for NBC News, researchers in Australia have found that one prevalent hospital superbug, which is already resistant to multiple drugs, is becoming more tolerant to the alcohol in hand sanitizers.
In the early 2000s, Australia began to systematically use alcohol-based hand sanitizers in its hospitals. Infections caused by some types of drug-resistant bacteria, like methicillin-resistant Staphylococcus aureus (MRSA), subsequently went down. But to the surprise of medical researchers, disinfectants did not seem to do much to curtail the spread of bacterial infections caused by so-called superbug vancomycin-resistant Enterococci (VRE); in fact, VRE infections in Australian hospitals started going up.
Vancomycin-resistant Enterococci are types of bacteria that can live in the intestines and female genital tract, and they don’t typically cause disease in healthy people. But among compromised patients—like those with weakened immune systems due to cancer treatments or organ transplants—VRE can cause urinary tract, wound and bloodstream infections. VRE bugs are hard to treat because they are resistant to several types of antibiotics.
And Australia is not the only country struggling to clamp down on the spread of VRE in hospitals. According to Melody Schreiber of NPR, nations around the world have seen increasing rates of enterococcal infections, despite greater use of hand sanitizers.
To find out why VRE infections might be on the rise, researchers at the Peter Doherty Institute for Infection and Immunity in Melbourne studied 139 samples of Enterococcus faecium, a strain of vancomycin-resistant Enterococci, collected from two Melbourne hospitals between 1997 and 2015, reports Live Science’s Rachael Rettner. The researchers exposed the samples to alcohol solutions, and found that the samples collected after 2010 were 10 times more tolerant to alcohol than the earlier ones. Their results are described in a recent paper in the journal Science Translational Medicine.
As NPR’s Schrieber points out, the bacteria don’t yet seem to be fully resistant to hand sanitizers. But the newer Enterococcus faeciumi samples were able to survive for longer periods of time after being exposed to alcohol solutions. In fact, it took a 70-percent alcohol mixture to kill the bacteria completely, which is somewhat disconcerting, since hand sanitizers typically boast 60 percent alcohol concentrations.
In the second phase of their experiment, the researchers took four Enterococcus faeciumi samples, two of which were shown to be alcohol tolerant, and smeared them over mice cages. They then took hospital-grade disinfectant wipes, wiped down the cages, and let mice crawl around inside for an hour. Subsequent testing revealed that mice exposed to the alcohol-tolerant samples were more likely to have Enterococcus faecium colonizing in their guts.
“It shows that it is not just a laboratory phenomenon that we are measuring here; we are showing this characteristic [of the bacteria] transfers into being able to escape a standard infection control procedure,” Timothy Stinear, one of the authors of the new paper, tells Nicola Davis of the Guardian.
When the researchers analyzed the DNA of the Enterococcus faecium samples, they found that the alcohol-tolerant bacteria had several mutations in genes connected to metabolism, which could explain their ability to withstand alcohol disinfectants. But as Stinear notes in a video posted by the Doherty Institute, scientists do not fully understand how and why Enterococcus faecium has evolved this adaptation. It is possible that the bacteria are simply becoming resistant to hand sanitizers, but something more complex could be at work.
“It might also be that the bacterium is doing another trick: it’s becoming better able to live in the low PH of our gut, and that adaptation coincidentally confers resistance to alcohol,” Stinear explains. “That extra advantage that it has, by being able to grow in our gut, means that it’s actually harder to kill when it gets on our hands.”
Another limitation of the new study is its size: the scientists only focused on Australian hospitals. Further research is needed to determine whether the same patterns of alcohol tolerance are present in other hospitals around the world. In the meantime, the researchers say, hospitals might want to consider using disinfectants with both alcohol and chlorhexidine, another bacteria-killing compound, to try and cut down on the spread of alcohol-tolerant bugs.
“The alcohol hand-hygiene programs have been highly successful, particularly at controlling MRSA, but also other types of hospital infections, and I would strongly advocate that we continue,” study co-author Paul Johnson says in the Doherty Institute video. “However … we may have to add additional control measures for VRE outbreaks.”