Antibiotics enable E coli bugs to mutate, grow faster

Antibiotics may cause bacteria to mutate into "uberbugs" which reproduce much faster, say scientists who found that a bug which causes severe stomach pain, diarrhoea and kidney failure in humans had increased resistance after each round of drug treatment.

Researchers at University of Exeter in the UK exposed E coli bacteria to eight rounds of antibiotic treatment. They found that mutated E coli reproduced faster than before encountering the drugs, and formed populations that were three times larger because of the mutations.

This was only seen in bacteria exposed to antibiotics - and when researchers took the drug away, the evolutionary changes were not undone.

"Our research suggests there could be added benefits for E coli bacteria when they evolve resistance to clinical levels of antibiotics," said Prof Robert Beardmore of University of Exeter.

"Bacteria have a remarkable ability to rearrange their DNA and this can stop drugs working, sometimes in a matter of days," he said. "While rapid DNA change can be dangerous to a human cell, to a bacterium like E coli it can have multiple benefits, provided they hit on the right changes."

The researchers tested the effects of the antibiotic doxycycline on E coli as part of a study of DNA changes brought about by antibiotics. The E coli "uberbug" that subsequently evolved was safely frozen at -80°C and the scientists used genetic sequencing to find out which DNA changes were responsible for its unusual evolution.

"Our best guess is that losing viral DNA stops the E coli destroying itself, so we see more bacterial cells growing once the increase in pump DNA allows them to resist the antibiotic," said Carlos Reding from the University of Exeter.