New superbug breaks through the last line of antibiotic defense

Common bacteria living on our skin has raised a red flag for scientists concerned with the rise of superbugs, as new research reveals the spread of a new type of drug-resistant infection around the globe. Some sub-strains of the bacteria have now outfoxed the last known antibiotics that may be able curtail it, raising the very real possibility that the infections it causes will essentially be untreatable.

To say the emergence of drug-resistant bacteria is a global health concern would be putting it mildly. Superbugs that have evolved to resist our current crop of antibiotics threaten to return the world back into the "dark ages of medicine," according to one UK government report. That same report predicts that if action is not taken, superbugs could kill up to 10 million people a year by 2050.

Many may be familiar with the human pathogen Staphylococcus aureus, more commonly referred to as staph, which itself has evolved to become resistant to methicillin. But it has a little known relative living in its shadows that is giving medical researchers fresh cause for concern.

Staphylococcus epidermidis (S. epidermidis) lives on the skin of all humans and is actually the leading cause of hospital-acquired infections, though a manageable one with an antibiotic called vancomycin routinely deployed to treat it. In more difficult cases, vancomycin is combined with another antibiotic called rifampicin to put a patient on the road to recovery.

But scientists are now calling for a rethink in how we treat S. epidermidis infections, in light of a peculiar case where a patient was admitted to hospital in 2012 for a simple procedure and remained there for months after contracting a highly resistant infection. Dr. Jean Lee from the University of Melbourne's Department of Microbiology, together with her consultant and PhD supervisor Professor Ben Howden, began to investigate whether this drug resistance was a one-off case, or something more disconcerting.

Over the following six years, the team sequenced the entire genetic code of S. epidermidis and uncovered three lineages, comparing the mutations to similar cases from across the globe. Indeed, the same mutations giving the bugs their antibiotic resistance showed up in every one of the 10 countries examined by the scientists, across the UK, Europe and America.

"Our findings demonstrate that three lineages of S. epidermidis that are resistant to all the standard antibiotics that would be normally be used for treatment have spread internationally," Lee explains to New Atlas. "In Europe, a few of the isolates have also gained additional antibiotic resistance to the two 'last-ditch' antibiotics that are tried when all the usual options have failed. Infections with these strains are potentially untreatable."

Those last-ditch antibiotics Lee refers to are not standard treatments but "salvage drugs" with limited clinical evidence available as to their efficacy. Lee says there are a handful of reports of bacteria exhibiting extreme drug resistance, with S. epidermidis now among them. While the researchers know it has caused serious infections, their work so far is yet to establish exactly how many, or the degree of their severity.

The findings have, however, prompted them to turn their attention to how the bug is spreading and what is giving rise to its resistance. A lot of patients contract S. epidermidis infections in intensive care, where their immune system is already compromised and they are often injected with catheters or lines to administer drugs, granting the bug entry to their bodies.

"Catheters and other implanted devices are frequently impregnated with antibiotics as a strategy to prevent infection, however this approach may be promoting the development of resistance," says Professor Howden. "Also, these infections are most prevalent in intensive care, where patients are sickest and strong antibiotics are liberally prescribed, promoting the development of additional resistance."

The scientists are now focusing on pinning down how the bug is being passed to patients, and then learning more about its spread internationally. This will hopefully help them draw up new treatment guidelines that can start to curtail its effects.

"We know what we're currently doing is just leading to more resistance," says Professor Howden. "So, we urgently need to think about what we should be recommending instead. There is an urgent need for an international monitoring system to understand the prevalence and impact of S. epidermidis and to systematically measure antibiotic resistance and infections due to this pathogen."

The research was published in the journal Nature Microbiology.

Source: University of Melbourne