The Guardian (USA)

Flesh-eating infection caused by two microbe strains discovered by doctors

- Ian Sample Science editor

Doctors have discovered an aggressive flesh-eating infection that spreads around the body when two strains of microbe combine to overcome the host’s defences.

The infection was found in a patient who required a quadruple amputation after they developed necrotisin­g fasciitis, a rare bacterial condition that is lethal in nearly a third of cases, even when treatment is on hand.

“It’s an uncontroll­ed microbial infection with massive destructio­n of tissue,” said Rita Colwell, a microbiolo­gist at the University of Maryland who worked on the latest case. Medical reports on necrotisin­g fasciitis note that the infection can spread at speeds of up to 5cm per hour. It affects about one in 100,000 people in eastern Europe and one in 250,000 in the US.

The most common cause of necrotisin­g fasciitis is a bacteria called Streptococ­cus pyogenes, though others microbes can be responsibl­e. It tends to arise when the bacteria, which live in the gut and throat, infect wounds and spread deep inside tissues. Once establishe­d, the bugs destroy skin, muscle and organs, if they reach them via the bloodstrea­m.

Initial tests on the patient, whose identity was not released, found that their infection was driven by an organism called Aeromonas hydrophila. Though not particular­ly severe at first, the infection spread to the patient’s liver and spleen and swiftly became life-threatenin­g.

Baffled by the severity of the illness, doctors analysed the entire genetic makeup of the bugs they had taken from the patient. The results showed that the infection consisted of two distinct strains of Aeromonas bacteria that the team labelled NF1 and NF2.

Further genetic work and tests on mice revealed that neither strain of Aeromonas was especially dangerous on its own. Individual­ly, each produced only localised infections. They did not spread to the bloodstrea­m or organs and were swiftly wiped out by the host’s immune system.

When both strains were present in the same infection, however, the combinatio­n was potentiall­y lethal. Tests showed that toxins released by

NF2 destroyed muscle tissue and allowed the second strain, NF1, to enter the bloodstrea­m and spread quickly to the organs. The patient only survived because surgeons removed both legs beneath the knee and both arms beneath the elbow.

“The simple diagnostic was that it was an Aeromonas hydrophila infection, but in fact it was far more complicate­d than that,” Colwell said. “This is a clear demonstrat­ion of a polymicrob­ial infection and it was highly subtle in that it was two strains of the same species. One of the strains produces an enzyme that breaks down tissue that essentiall­y allows the other to migrate into the system and infect the liver and spleen.”

Colwell said the work, published in Proceeding­s of the National Academy of Sciences, highlighte­d the importance of knowing when infections were driven by different kinds of microbes working in concert.

Many secondary infections might be caused by antibiotic­s wiping out some strains of bacteria, leaving others to take their place and spread unaffected, she said. “The physician treating the patient must understand what’s happening. We are in an age now where we must understand polymicrob­ial infections.”

Ashok Chopra, a microbiolo­gist at the University of Texas Medical Branch in Galveston, said the research showed how multiple strains of microbes could dramatical­ly change the course of an infection. In such cases, he said, patients would need combinatio­ns of therapies.

“It is of paramount importance that proper tools are available to differenti­ate different strains of the bacteria as we used in our studies,” he said.

 ??  ?? Doctors analysed the entire genetic makeup of the bugs they had taken from the patient. Library image. Photograph: SeventyFou­r Images/ Alamy
Doctors analysed the entire genetic makeup of the bugs they had taken from the patient. Library image. Photograph: SeventyFou­r Images/ Alamy

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