Flesh-eating bacteria: Scientists identify the perpetrator

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By all accounts, flesh-eating disease is as dreadful as it sounds. The disease is caused when the dangerous group A Streptococcus bacteria march relentlessly through the body, devouring tissue. Group A Strep also causes many other illnesses, such as strep throat, impetigo and toxic shock syndrome. When Strep invades areas of the body where it’s normally not found, such as the blood and organs, it can be deadly. About 10% to 15% of people with invasive group A Strep die from their infection, and 25% of those with flesh-eating disease and 35% of those with toxic shock syndrome die.

Those cheery facts lead us to the good news: Scientists are honing in on how to stop this bugger. Experiments at UC San Diego School of Medicine and the Rady Children’s Hospital in San Diego have found that Strep survives and spreads in the body by disabling a key immune defense molecule. The study is published today in the journal Cell Host & Microbe.

Previous research found that Strep bacteria change their pattern of gene expression during an infection, releasing a massive amount of a substance called SpyCEP. The new study shows that SpyCEP inactivates an immune system molecule that controls the body’s white blood cells and their ability to fight bacteria. In the presence of SpyCEP, white blood cells function slower and weaker. The immune-blocking effect of SpyCEP also seems to allow other bacteria to invade the infection site, thus contributing to the need for complex antibiotic regimens to treat the illness.

In lab studies, the UCSD team knocked out the gene encoding the SpyCEP from a strain of Strep that was taken from a patient with flesh-eating disease. When the Strep bacteria lacked SpyCEP, the body effectively fought off the infection and the Strep could not spread when injected into the skin of an experimental mouse.

The understanding of these biological shenanigans should help researchers in their quest to find ways to stop group A Strep in its nasty tracks. For more information on group A Strep, see this fact sheet from the Centers for Disease Control and Prevention.

-- Shari Roan