Michigan State University researchers led by Professor Thomas Whittam, said the technique involves very small genetic changes called single nucleotide polymorphisms, or SNPs. Using SNPs, scientists analyzed 96 markers, making genetic analysis of pathogenic bacteria possible at a rate never before accomplished.

"It used to take three months to score one gene individually," Whittam said. "Now, we are working on a new, more rapid system that can do thousands of genes per day."

The team studied the DNA of more than 500 strains of a particularly dangerous member of the E. coli family, O157:H7. In collaboration with David Alland of the University of Medicine and Dentistry of New Jersey, Whittam discovered individual bacteria could be separated into nine major groups, called clades.

Whittam discovered the different clades produced different kinds of toxins from O157:H7 in varying amounts based on their DNA.

"For the first time, we know why some outbreaks cause serious infections and diseases and others don't," Whittam said.

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