Antibiotics designed to kill bacteria can actually accelerate their growth, new research has shown.
The findings are a new and unwelcome twist to the growing problem of drug-resistant bugs. Eschericia coli (E.coli) bacteria exposed to repeated rounds of antibiotic treatment not only survived but also began to multiply more quickly. After eight treatment sessions in four days the bugs formed populations three times larger than they would have done without the drug.
E.coli is a common germ that contaminates food and water and can cause severe stomach cramps, diarrhoea and kidney failure.
Lead scientist Professor Robert Beardmore, from the University of Exeter, said: "Our research suggests there could be added benefits for E.coli bacteria when they evolve resistance to clinical levels of antibiotics.
"It's often said that Darwinian evolution is slow, but nothing could be further from the truth, particularly when bacteria are exposed to antibiotics. Bacteria have a remarkable ability to rearrange their DNA and this can stop drugs working, sometimes in a matter of days. While rapid DNA change can be dangerous to a human cell, to a bacterium it can have multiple benefits, provided they hit on the right changes."
The team was investigating the effects of the antibiotic doxycycline on E.coli DNA. After repeated exposure to the drug, the bacteria evolved into a mutant form with resistant characteristics such as an ability to pump the antibiotic out of its cells. Another change was likely to see the bacteria switch from a surface "biofilm" coloniser to an organism more adapted to spread through the bloodstream.
Co-author Dr Carlos Reding said: "You see biofilms in a dirty sink when you look down the plughole. But our study used liquid conditions, a bit like the bloodstream, so the E.coli could give up on its biofilm lifestyle in favour of increasing cell production."