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Disinfectant misuse could help create superbugs

December 29, 2009 |  3:05 pm
Pseudomonas aeruginosa: A drug-resistant form of a bacterium usually associated with hospital-acquired infections led to the death of Brazilian beauty queen Mariana Bridi Disinfectants may be a double-edged sword in the fight against hospital-borne diseases, scientists say. 

According to a study to be published in January’s issue of Microbiology, researchers from the National University of Ireland in Galway slowly introduced higher levels of disinfectant to lab cultures of Pseudomonas aeruginosa, which lives in the soil and water around us. It can’t seriously hurt healthy people (it’s been implicated in “hot tub itch” and “swimmer’s ear”) but preys on those with compromised immune systems. This opportunistic pathogen can infect the lungs, joints, burn wounds, take advantage of a compromised urinary tract or cause blood diseases. The bacterium can live in man-made environments and colonize catheters and other medical equipment. It’s ideally suited for hospital transmission – the Online Textbook of Bacteriology calls it “the fourth most commonly-isolated nosocomial pathogen accounting for 10.1 percent of all hospital-acquired infections” – but it can infect anyone whose defenses have been weakened, whether from chemotherapy or diabetes, cystic fibrosis or AIDS. 

After gradually upping the dose of benzalkonium chloride, an antiseptic used in products that include eyedrops and wet wipes, researchers had on their hands a Frankensteinian pathogen that showed a 12-fold resistance to the common disinfectant. (Generally, showing four or five times the normal resistance level is enough to earn a newer, nastier disease “superbug” status.)

Even worse, that same variant of P. aeruginosadisplayed a whopping 256-fold increase in resistance to the antibiotic ciprofloxacin – even though it had never been exposed to the drug before. That’s worrisome, since the commonly prescribed Cipro has been used to treat such high-profile pathogens as anthrax spores.

The upshot? That hospitals that don’t use enough disinfectant to kill every last bacterium on a given surface could provide an ideal breeding ground for new superbugs. These mutations could become virtually immune to prevention and treatment.

“The message, for heaven’s sake, is use disinfectants properly,” lead author Gerard Fleming said in an interview. “The first line of defense is disinfection. The second line of defense is antibiotics.”

By misusing disinfectants, he concluded, “You're making an environment where you've now lost the first and second lines of defense.”

There’s a dangerous tendency toward using disinfectants as a clean-all, Fleming said, when there was a much more potent, proven remedy to rid oneself of germs.

“Soap and water. I am not messing with you,” Fleming said. “Why doesn’t the surgeon, when he’s going into the theater, just take a hand sanitizer? Why does he go to the sink and scrub and scrub and scrub? Because he’s physically removing the bacteria.”

-- Amina Khan

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