How flesh-eating bacteria exploded into epidemic

A strain of flesh-eating group may affect you in various ways - some of them fatally - and scientists have now discovered how this bacteria exploded into a worldwide epidemic.

Only four tiny modifications to group A Streptococcus bacteria caused it to explode into a worldwide epidemic, the study said.

"The first two events were the acquisition of two bacterial viruses," said infectious disease pathologist James Musser of the Houston Methodist Research Institute in the US.

Bacteria, just like humans, can get infected by viruses, Musser noted.

Sometime in the 1980s, these viruses infected a single bacterial cell of group A Strep, transferring genes to the bacterium that allowed it to produce novel toxins.

This is known as horizontal gene transfer, the acquisition of a trait not by mutations in reproduction, but from an outside source.

The third event was a regular old mutation in the genes of the bacteria, which produced an upgraded variant of one of the toxins.

The fourth and final event that immediately preceded the epidemic was an attack from another virus, which had previously attacked another strain of group A Strep, picking up some of its genetic material.

When it hit the epidemic strain, it transferred this material, which encoded two additional toxins and caused the strain to churn them out in massive quantities, said the study.

"This whole process ultimately resulted in two important character changes to the organism, which were the ability to cause an increased number of infections, and an increased severity of infection," Musser said.

In the biggest bacterial study of its kind to date, scientists sequenced the genomes of thousands of strains of group A Strep.

The study appeared in the journal Proceedings of the National Academy of Sciences.