Soil bacteria and bacteria that cause human diseases have recently swapped at least seven antibiotic-resistance genes, researchers at Washington University School of Medicine in St. Louis report Aug. 31 in Science. According to the scientists, more studies are needed to determine how widespread this sharing is and to what extent it makes disease-causing pathogens harder to control.

"It is commonplace（平凡的） for antibiotics to make their way into the environment," says first author Kevin Forsberg, a graduate student. "Our results suggest that this may enhance drug resistance in soil bacteria in ways that could one day be shared with bacteria that cause human disease."

Among the questions still to be answered: Did the genes pass from soil bacteria to human pathogens or vice versa（反之亦然）? And are the genes just the tip of a vast reservoir of shared resistance? Or did some combination of luck and a new technique for studying genes across entire bacterial communities lead the scientists to discover the shared resistance genes?

Humans only mix their genes when they produce offspring, but bacteria regularly exchange genes throughout their lifecycles. This ability is an important contributor to the rapid pace of bacterial evolution. When a bacterial strain develops a new way to beat antibiotics, it can share the strategy not only with its descendants but also with other bacteria.

Earlier studies by other scientists have identified numerous resistance genes in strains of soil bacteria. However, unlike the seven genes described in this report, the earlier genes were dissimilar to their analogs in disease-causing bacteria, implying that they had crossed between the bacterial communities a long time ago.

Most of the antibiotics used to fight illness today originated from the soil. Bacteria use the antibiotics, in part, as weapons to compete with each other for resources and survival. Scientists have long acknowledged that gives environmental bacteria an evolutionary incentive to find ways to beat antibiotics.

"We wanted to try to get a broader sense of how often and extensively antibiotic-resistance genes are shared between environmental bacteria and pathogens," says senior author Gautam Dantas, PhD, assistant professor of pathology and immunology.