Bacteria have a penchant for reinventing themselves, speedily adapting to new hosts, new conditions, and new antibiotic countermeasures. Now scientists have uncovered what may be a secret of that versatility, at least for certain microbes: individuals with a high rate of genetic mutation, says a Report  in today's issue of Science.
In just the past few years, strains of Escherichia coli have emerged that can thrive in salted foods like sausage or acidic foods such as apple juice, and certain strains of Salmonella have developed the ability to resist food-processing temperatures that kill other organisms. Although bacteria have a seemingly limitless capacity to alter their genes by swapping bits of DNA between strains, this mechanism doesn't seem enough to account for the swift pace of change and the high variability of E. coli and other strains.Thomas Cebula of the U.S. Food and Drug Administration (FDA) wondered if this rapid evolution is being driven by microbes capable of much faster-than-normal variation. To test the hypothesis, his team turned to a rogues' gallery of organisms: ''We [had] a collection of all the outbreak strains we've collected over the years,'' he says. They used antibiotics to screen for ''hypermutable'' strains that quickly develop drug resistance. ''We were surprised at how often we found mutators,'' Cebula says. What's more, the mutators were defective in genes needed for a type of DNA repair. Thanks to this flaw, such bacteria would alter their own genes faster than normal as well as take in DNA from other bacteria more readily.Because the genes for antibiotic resistance often travel between bacteria on foreign DNA, the FDA group's findings could account for the rapid spread of resistance among Salmonella and E. coli strains, says Philip Hanawalt, an expert on DNA repair at Stanford University. Because the findings may apply to other pathogenic bacteria as well, he says, ''this work has very far-reaching implications and is even a bit ominous.''
The findings also sound a warning note about food processing, says University of Florida food scientist Douglas Archer. Indeed, in response to the latest E. coli outbreak in the United States, the government is now considering a requirement that all fruit juices be pasteurized.