Antibiotic-resistant bacteria and antifungal-resistant fungi are a worrying phenomenon. According to a recent study, a new concern may be developing: alcohol-tolerant bacteria.

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Why are Enterococcus faecalis (pictured) infections on the rise?

A number of bacteria species are already resistant to a range of antibiotics; the infections they cause are difficult to treat, posing an ever-increasing threat to patients and staff.

Because of the growing numbers of so-called superbugs, hospitals have introduced more stringent cleaning routines.

Part of the regimen involves alcohol-based disinfectants, such as hand rubs, positioned in and around hospital wards. Since their introduction, there has been a significant reduction in the number of hospital-based infections.

Containing 70 percent isopropyl or ethyl alcohol, alcohol-based hand rubs kill bacteria quickly and effectively.

Over recent years, researchers have noted a steady rise in the number of serious infections caused by one particular drug-resistant bacterium — Enterococcus faecium. Despite the wide use of alcohol-based disinfectants, E. faecium is now a leading cause of hospital-acquired infections.

Dr. Sacha Pidot and his colleagues at the University of Melbourne in Australia set out to understand whether this increased infection rate might be because the bacterium is growing resistant to alcohol. Their findings were published this week in the journal Science Translational Medicine.

To investigate, the researchers used bacterial samples from two hospitals in Melbourne — Austin Health and Monash Medical Centre. In all, they tested 139 samples of E. faecium, isolated from 1997–2015. They assessed how well each sample tolerated diluted isopropyl alcohol.

After analysis, it became clear that the samples taken after 2009 were significantly more tolerant of alcohol than those taken before 2004.

In a second experiment, they allowed bacterial samples to grow on the floors of mouse cages that had been cleaned using alcohol-based disinfectants. Mice were placed in the cages for 1 hour before being moved to clean cages for a further 7 days. After that time, they were screened for infection.

The researchers found that the more recently isolated, alcohol-tolerant strains of E. faecium colonized the resident rodents more successfully.

To round off their investigation, the scientists delved into the genome of E. faecium. They found that the strains that were more resistant to alcohol displayed mutations in certain genes involved in metabolism; these genetic changes appeared to be responsible for their more hardy constitution.

Because this study focused on samples from just two hospitals in one city, the authors are wary of the limitations and call for further investigation. Although these are early findings, it is important to consider what alcohol-resistant bacteria could mean in real-life clinical settings.

[T]he development of alcohol-tolerant strains of E. faecium has the potential to undermine the effectiveness of alcohol-based disinfectant standard precautions.”

Dr. Sacha Pidot

Bacteria predate us by millennia; they have survived countless global disasters. Their ability to adapt has been tested and honed over trillions of generations. They seem capable of crossing any flimsy barrier that humans put in their way.

Because the potential ramifications of this study are serious, more studies are likely to be published over the coming months.