By Marlowe Hood

PARIS, Dec 28, 2009 (AFP) - Disinfectants commonly used in homes and medical facilities can boost the resistance of some bacteria to life-saving antibiotics, according to a study released Monday.

The findings shed light on how at least one pathogen - Pseudomonas aeruginosa - spreads, and could apply to other hospital superbugs as well, the authors say.

P. aeruginosa, responsible for one-in-10 hospital-acquired infections, is a so-called "opportunistic" bacteria that attacks people with weakened immune systems.

It typically infects the pulmonary and urinary tracts, as well as burns and puncture wounds.

In laboratory experiments, researchers showed that the bug can rapidly mutate, building resistance to progressively higher doses of a disinfectant known as BSK, or benzalkonium chloride.

Safe for humans, BSK is widely-used in cleaning and disinfecting products to kill bacteria, fungi and algae.

The DNA-altered bacteria were able withstand concentrations of BSK up to 400 times greater than the non-mutated strain.

More critically, they also developed a resistance to an antibiotic, ciprofloxacin, even though they had never been exposed to the drug.

Ciprofloxacin is a front-line medication in the fight against several bacterial infections, and is also the drug of last-resort against the deadly disease anthrax.

"This is very, very worrying," said Gerard Fleming, a professor at the National University of Ireland in Galway, and main architect of the study.

"We found that in both cases - for the disinfectant and the antibiotic - the [mutated] bacteria was taking them in, but expelling them just as quickly.

It would be like trying to pump air into a bicycle tire with a huge hole in it," he told AFP by phone.

The disinfectant-resistant strain of P. aeruginosa built up immunity against ciprofloxacin up to ten times more effectively than did the baseline bacteria, the study reported.

In further experiments, Fleming and colleagues put the two strains together in an environment containing a diluted dose of disinfectant, such as might be found in a hospital or home.

The mutated bugs were "highly competitive" with the non-mutated ones, said Fleming: "They outgrew the so-called 'sensitive' strains so rapidly it was hard to believe."

"That means that we have a problem - disinfectant may proliferate antibiotic resistance," he added.

Fleming hastened to add that this did not mean that disinfectants should not be used at all.

"They are quite important as a first-line defence. The message is to use them properly - don't water them down to concentrations where they are no longer effective," he said.

The findings, to be published next month in the journal Microbiology, also point to the possibility that other drug-resistant hospital killers - such as MRSA (methicillin-resistant Staphylococcus aureus) and C-diff (Clostridium
difficile) - could spread and build up immunity to antibiotics in the same way.

"We need to look at this very carefully. A lot more work needs to be done on this one," said Fleming.