Hamilton lab unravels virus mystery-Research shows how strep virus turns into flesh-eater

What causes a perfectly predictable little bug like A Streptococcus – the nasty buggers
behind strep throat – to morph into a flesh-eating monster?

By JENNIFER McKEE of the Missoulian State Bureau

For years, scientists have known that the same bug that causes the common and treatable strep,
along with a host of other illnesses, also causes the so-called "flesh-eating disease" and other much
more virulent infections. But just what caused some strains of the bacteria to go bad was unknown.

New research by scientists at the Rocky Mountain Laboratories in Hamilton and others answers that
question with a most unlikely culprit: viruses that infect bacteria. Their study was published this week
in the online version of Proceedings of the National Academy of Scientists, a scientific journal.

The team, headed by James Musser, chief of the Laboratory of Human Bacterial Pathogenesis, an
arm of the Rocky Mountain Labs, found that about 12 percent of the chromosome of the most virulent
and invasive strains of strep bacteria was actually genetic material from special viruses that only
infect bacteria. What’s more, those virus genes caused the development of toxins that closely
resemble snake venom.

"That was not suspected at all," Musser said. "That was quite a shock."

The scientists mapped the genome of an especially nasty strain of strep – taken from a person with
toxic shock syndrome – that is especially deadly and known to cause severe infections.

The genome was "littered" with special viruses called bacteriophages, which only infect bacteria.
Bacteriophages blend their genetic material with that of their host, Musser said, creating "a
chromosome within a chromosome." It’s that outside DNA that makes the strain of strep the
scientists studied so deadly.

While science has known of bacteriophages for decades, Musser said his team’s research was the
first time anyone showed how great a role the tiny viruses can play in the deadliness of disease.

So-called "flesh-eating disease" is caused by this same strain of strep. Such deadly infections
started becoming more frequent over the last 15 years, Musser said. He thinks some kind of "random
event" allowed the bacteriophage to enter into the genome of strep, but said that no one knows why
it’s becoming more common.

There are other questions, too. While it’s obvious, Musser said, that traditional antibiotics are
effective against virus-tainted bacteria, no one knows if they work as well against tainted bacteria as
nontainted.

Now, the team is studying the snake venom-like toxin they discovered, hoping it might prove fertile
ground for developing new kinds of treatments against especially deadly strains of strep.

Rocky Mountain Labs is part of the National Institutes of Health.

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