Using disinfectants, such as those found in hand sanitizers, could lead to the growth of superbugs resistant both to the cleansers and to antibiotics, researchers warn.

The findings are published in the January 2010 issue of the journal Microbiology.

Scientists at the University of Ireland in Galway found that when they added the disinfectant benzalkonium chloride to common bacteria called Pseudomonas aeruginosa, increasing the amount of the germ-fighting solution over time, the bacteria learned how to survive. They also became able to withstand a commonly prescribed antibiotic, ciproflaxin, even though they had never come in contact with it.

Benzalkonium chloride is found in hand sanitizers, wet wipes and moist towelettes.

Pseudomonas aeruginosa bacteria cause urinary tract, respiratory system, bone and joint and gastrointestinal infections and can be lethal in people who are immuncompromised, such as those with cystic fibrosis, cancer or AIDS. It is increasingly being found in hospital settings and has become an important cause of hospital-acquired infections.

The researchers discovered that over time the bacteria became more efficient at ridding their cells of both the disinfectant and antibiotic. They also found that a mutation in their DNA made them resistant to antibiotics.

The researchers say the findings illustrate how dangerous a mix of weak disinfectant and Pseudomonas aeruginosa can be.

"In principle, this means that residue from incorrectly diluted disinfectants left on hospital surfaces could promote the growth of antibiotic-resistant bacteria," Dr. Gerard Fleming, lead author of the study, said in a release. "What is more worrying is that bacteria seem to be able to adapt to resist antibiotics without even being exposed to them."

The authors suggest more studies be conducted on the interplay of multiple disinfectants in eradicating bacteria and preventing the development of antibiotic-resistant strains.