In the ongoing battle against menacing microbes, some scientists are raising a new concern: The widespread use of antimicrobial soaps may cause problems worse than the ones they aim to cure. A report last month from Tufts University School of Medicine says a substance used in these soaps, and in plastic toys and other "antibacterial" products, behaves a lot like an antibiotic -- and could possibly encourage bacteria to mutate in ways that make them impervious to antibacterials, including antibiotics. Microbiologist and physician Stuart B. Levy, who led the research, found that the antibacterial agent triclosan, commonly used in soaps, fabrics and plastics, works by targeting an enzyme important for the formation of lipids or fats that make up cell walls in the bacteria E. coli.
Prior to this work, it had been thought triclosan was a general biocide like alcohol or peroxide that worked by dissolving the membrane walls of bacteria.
In such nonspecific killers, Levy says, "we don't have to worry about resistance emerging, but we found triclosan has a target. That put everybody back on his heels. It wasn't supposed to have a target."
Antibiotics aim at a specific substance within bacteria. If triclosan does that, too, he says, it means bacteria can evolve into forms that can resist triclosan's effect.
Industry representatives advise caution in reacting to the report. "There are so many things that are not known as to what the research may mean," says Gerald McEwen, vice president of science for the Cosmetic, Toiletry and Fragrance Association. "Jumping to the conclusion that by using antibacterial products somehow we're going to end up with germs that are going to overrun the world is fine fodder for a science fiction movie, but it's not borne out by any (research) we have today."
But pediatrician Philip Landrigan, chair of the department of community and preventive medicine at Mount Sinai School of Medicine in New York, says the report and the questions it raises should be taken seriously.
"Spraying antibiotics around in the environment, whether as soaps, additives to animal feeds or given to children, are behaviors that are going to come back to haunt us," he says. "They will create selection pressures to force the rapid evolution of bacteria into superbugs."
Another source of concern in liquid soaps -- including some antimicrobials -- is a recent report from the National Toxicology Program (NTP), part of the National Institute of Environmental Health Sciences, that found an ingredient in many bubble baths and soaps causes cancer in mice.
The chemical, diethanolamine, or DEA, which is a foaming agent, has not been proved to cause cancer in humans, the NTP report says. But, it says, "the findings alert us to that potential," and "the Food and Drug Administration is now reviewing this information . . . to assess overall risk to humans."
Parents who have stocked their kitchens and bathrooms with these products should not "feel guilty that they've done anything wrong," Landrigan says. "But now that this information has come to light," he advises parents "to switch to products that are free of DEA and not antibacterial."
McEwen disagrees. While the potential public health risk from antimicrobials is theoretical, he says, the benefits are clear. "They reduce the microbiological flora, and in so doing, we believe, they reduce the incidence of disease."
And he challenges the validity of the NTP study, in which DEA was applied daily to the skin of rats and mice for two years. In mice, the incidence of liver and kidney tumors increased.
"The major concern" with the study, McEwen says, "was that the experiment with the mice was not set up in such a way as to ensure the mice would not ingest a large amount of the material that was applied." He says it's possible that the cancer-causing effect was related to consumption of the DEA, which was applied in an alcohol base. "The alcohol itself could lead to the livers being activated in the mice, and put them into a position where they are more likely to develop tumors," he says.
Humans don't eat DEA, he says, and "the time (the substances) spend resident on the skin is very small. The amount that might penetrate the skin is also very small. Therefore, even if the DEA were acting on these animals, the likelihood of the risk of this being something FDA would take action on is small."
Toxicologist Jenan Al-Atrash, director of human health and safety for the Soap and Detergent Association, also downplays the concern over triclosan, calling Levy's findings "preliminary." While they "might be true," she says, his work "needs to be replicated." She says triclosan has "been used in various forms for the past 30 years or so," without causing any known antimicrobial resistance to develop.
But, "you can say the same thing about some antibiotics," says Levy, who is president of the Alliance for the Prudent Use of Antibiotics (www.antibiotic.org). "I'm concerned about kids thrown antibiotics at every sniffle, and homes full of antimicrobials."
Much remains to be learned about the effects of these products on microbes and on humans, Levy says.
"We have not looked for resistant mutants in households," he says, and he cautions that his recent study "is a lab experiment. It says triclosan acts like an antibiotic, it has an interesting target -- lipids in the cell wall -- and you can get resistant mutants. It says maybe it doesn't happen in the wild. But given enough time and drug, why shouldn't it select resistance as do antibiotics?"
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