Disinfectants designed to keep bacteria out of homes and hospitals could be fuelling the growth of superbugs. Scientists found that exposing infectious bacteria to increasing amounts of disinfectant turned the bugs into hardy survivors. The bacteria also developed resistance to the antibiotic, ciprofloxacin – despite not having previously encountered the drug.

The findings, reported in the January issue of the journal Microbiology, could carry serious implications for the spread of infections in hospitals.

The scientists, led by Dr Gerard Fleming from the National University of Ireland in Galway, found that the bacterium Pseudomonas aeruginosa adapted to disinfectant exposure by improving its ability to pump antimicrobial agents out of its cells. The bacterium, which is responsible for many hospital-acquired infections, also developed a DNA mutation that helped it resist ciprofloxacin-type antibiotics.

Exposure to small, non-lethal amounts of disinfectant encouraged the survival of resistant bacteria, Dr Fleming said. "In principle this means that residue from incorrectly diluted disinfectants left on hospital surfaces could promote the growth of antibiotic-resistant bacteria. What is more worrying is that bacteria seem to be able to adapt to resist antibiotics without even being exposed to them."