Research sheds new light on defense mechanisms of deadly Group A bacteria

Call them the Delta Force of the blood stream.

Polymorphonuclear leukocytes, a kind of cell in the human immune system, exist for one purpose: to find and destroy invading bacteria and fungi, said Frank DeLeo, a scientist at Rocky Mountain Laboratories in Hamilton.

By JENNIFER McKEE, IR State Bureau

They constantly patrol the blood and their methods are as concise and unpleasant as that of any predator. They eat their prey. Then — and DeLeo is not making this up — the cells secrete hydrogen peroxide and the active ingredient in household bleach to kill any hangers-on.

Such search-and-destroy cells generally wipe out every "unfriendly" in their path. But one group of nasties, Group A Streptococcus, can survive such battles. These are the same bacteria which bring us everything from strep throat to flesh-eating bacteria disease.

And they seem to be on the rise.

Scientists haven’t known exactly how strep manages to evade the immune system until now.

A study published this week in the online version of the Proceedings of the National Academy of Sciences by DeLeo and other scientists at Rocky Mountain Labs sheds new light on strep’s armor.

"We used a cutting edge technology to screen all of the genes (in strep) to see which ones are turned on when strep sees white blood cells," said Frank DeLeo, an investigator at the laboratory, which is under the umbrella of the National Institutes of Health.

They found that some of the genes allow the bacteria to block the attack of the body’s immune system. Others promote rebuilding the bacteria’s cell walls and repairing its own DNA, which the body’s immune system aims to destroy.

Scientists have known that Group A strep is becoming more common. It’s regarded as a "re-emerging pathogen," DeLeo said. But he said he wasn’t sure if this newly-discovered defense mechanism is behind the growth — and increased virulence — of strep outbreaks. It could be that strep has always been able to deflect immune system attacks, but science hasn’t known about it until now.

As for the rise in strep infections, DeLeo said he’s not sure if bacteria has changed or if people — and the conditions under which we live — has changed, making us more susceptible.

"Individuals are becoming immuno-compromised somehow," he said.

Strep is quite common, according to the Centers for Disease Control and Prevention, and accounts for several million cases of strep throat and impetigo, a mild skin disease, every year. In a small number of cases — about 600 a year — strep turns into flesh-eating bacteria, which can be deadly. The bacteria also causes about 300 cases of potentially deadly toxic shock syndrome each year.

The good news is that once scientists know which bacteria genes are confounding the immune system, they can build vaccines and other treatments to counter-attack, DeLeo said. By knowing how the bacteria evades the immune system, scientists can work on new drugs that will stop that process before it starts.

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