Antibiotics For A Meal

FLAME RETARDANTS, PCBs, and crude oil are all tasty snacks for certain bacteria, so why not antibiotics? New research shows that hundreds of bacteria found in a variety of U.S. soil samples can survive with only antibiotics as their carbon source.

Eighteen synthetic and natural-product-based antibiotics, such as ciprofloxacin, penicillin, vancomycin, and levofloxacin, were tested as proxies for a square meal among soil bacteria (Science 2008, 320, 100).

Some 600 types of bacteria have the metabolic machinery to subsist on a single type of antibiotic, says one of the researchers, Gautam Dantas, a postdoc in geneticist George Church's laboratory at Harvard Medical School. Although the bacteria with a penchant for antibiotics are not necessarily human pathogens, many are closely related to bugs that do infect us.

"This is highly significant work," comments Gerard D. Wright, a biochemist at McMaster University, in Hamilton, Ontario. "These organisms may not be pathogens themselves, but they could be sources of antibiotic resistance genes that could find their way into real pathogens through gene transfer."

The antibiotic-consuming bacteria were identified by placing soil samples in liquid media that contained only antibiotics as a carbon source and then isolating the surviving microbes.

Bacteria are notably difficult to culture outside their niche; less than 1% of bacteria will grow in a lab. So the hundreds of types of antibiotic-munching bacteria cultured by the researchers are likely an underestimation of the total numbers of the kinds of bacteria that can subsist on antibiotics in the environment, Dantas notes.

Stuart Levy, a medical microbiologist at Tufts University, finds the research "excellent" but interprets its results differently. "I think it's great that bacteria can eat up antibiotics in the environment," he says. By acting as bioremediators, these bacteria could mitigate the buildup of antibiotics in the environment, thereby reducing the overall selection pressure for the development of bacterial drug resistance, he says. "It would be great to harness their potential."