The deadly superbug MRSA has evolved a “bulletproof vest” to protect itself against a “last resort” antibiotic used to treat the infection.
Daptomycin is a highly potent antibiotic reserved for only the most serious cases.
Yet despite restricted use, the bacteria is still managing to create new defenses to protect itself.
The drug works by piercing the microbe’s external membrane and killing it. But, in a small percentage of cases, the drug fails. These patients often have no alternative therapies available to them and will likely die.
Now, scientists at Imperial College London have finally found out for the first time why the treatment is ineffective in some people.
Antibiotic defense could cause ‘a few hundred deaths in the UK’
Dr Andrew Edwards, an antibiotics researcher and microbiologist at Imperial, combined MRSA and daptomycin in a laboratory, before adding human blood to the mix. He found that the presence of the human immune system triggered the pathogen to start creating additional, never seen before defences.
He said: “The work here is basically showing a stress response. The bacteria is picking up on the fact that there’s an immune protein nearby. That causes the bacteria to get stressed and to essentially build a bulletproof vest that makes it much harder for antibiotics to kill them.
“If you’re on a last resort, you want it to work 100 per cent of the time, not 60 or 70 per cent of the time.
“Fortunately, there are not a huge number of people on these drugs but in about 20 or 30 per cent of them, it will fail and those people will die. We are probably looking at a few hundred deaths in the UK.”
MRSA is encompassed by a thin, fatty membrane which is the antibiotic targets and destroys, but it also has an extra coating made from thick sugars.
“This is a bit like a sieve or a mesh,” Dr Edwards said. “Normally it is quite thin and things can pass through it easily, including daptomycin.
“But what the bacteria does is build up the number of layers of that mesh until, much like if you overlay lots and lots of sieves, after a while nothing can get through.
“That layer is something that is there already, but the bacteria turbocharges it and really builds it up and makes it super thick, so that nothing can get through it.”
‘MRSA is like a Swiss army knife’
There is also the possibility that the added mesh-like layers of the sugar coating serve a secondary purpose and actually allow the bacteria to target different parts of a patient’s body.
“MRSA is like a Swiss army knife,” said Dr Edwards. “It can do anything. It’s an extremely adaptable pathogen that causes a broader range of different types of infection anything else.
“It infects the heart, the lungs, the joints and we don’t know how it disseminates so well.
“We think that this bulletproof vest might provide the bacterium with a way of interacting. It might have lots of adhesive proteins that allow it to interact with all these different sites and cause secondary infections.”
A recent study published in the Lancet found that antimicrobial resistance is an increasing problem and killed more than a million people in 2019 alone.
MRSA is often rife in healthcare settings and infects vulnerable people, preying on the frail.
Dr Edwards said that preliminary analysis shows MRSA is likely able to deploy its bulletproof jacket in response to more drugs than just daptomycin, including others seen by clinicians as part of the last line of defence.
Limiting exposure to these drugs is vital to restrict the progress of antimicrobial resistance. There are concerns that daptomycin, which was invented in the early 2000s and has recently expired its original patent, may be overprescribed.
The study was published in Nature Communications.