Entrenched

Conventional wisdom has always been that so-called "superbug" bacteria with antibiotic resistance lose their edge over their non-resistant bacteria cousins in the absence of the antibiotics, says New Scientist's Andrew Purcell. "Previous studies had found that the superbugs lose their competitive advantage once the antibiotics are no longer present. For instance, a voluntary ban by Danish farmers on the use of antibiotic growth promoters in chicken and pigs cut antibiotic resistance in the bacteria within the animals by over 90 percent," Purcell says. But a new study in PLoS Genetics suggests that this thinking may be wrong. The researchers focused on 10 E. coli strains that had already acquired genes for drug resistance from other organisms, Purcell says. The team found that when these strains evolved one of five mutations associated with resistance, five of the 50 resulting strains of bacteria could out-compete non-resistant bacteria, even in the absence of drugs. The same thing happened when the team used E. coli that had acquired resistance through mutation instead of horizontal gene transfer, Purcell adds. How this happens remains a mystery, the researchers say. They add that what is needed to kill these bugs is an alternative to antibiotics that will stop gene transfer between bacteria, though there is still no way to do this.