Friday, June 08, 2007

Antibacterial Products Can Help Breed Superdiseases

According to this Scientific American article, triclosan and chemicals like it help select for resistant bacteria because they have specific targets in bacteria that are shared by some antibiotics, and antibacterial products leave behind a weaker residue that contributes even more to resistance selection because it is not as effective at killing. Products like alcohol and bleach, on the other hand, evaporate leaving less residue, and they do nonspecific damage to the bacteria, so the risk of bacteria developing cross-resistance with antibiotics from traditional cleaners is less.

We are harming ourselves and our children by continued, widespread use of antibacterial products by breeding more resistant forms of bacterial diseases and by the contamination of our crops, streams, food, and water with these products. If this is true, none it should really be surprising despite the SciAm article's title. It makes sense, and the concern has existed for several years.


Rich said...

The data's pretty mixed on if antibacterials actually cause resistant bacteria. But even if that weren't a concern, the fact that most everyone agrees antibacterials do little more than normal soap should be cause enough to reject them.

John Paul said...

I would appreciate any data to the contrary that antibacterials, specifically triclosan, are a source of cross resistance. Anything funded by a manufacturer of triclosan does not count.

From the article:
As bacteria develop a tolerance for these compounds there is potential for also developing a tolerance for certain antibiotics. This phenomenon, called cross-resistance, has already been demonstrated in several laboratory studies using triclosan, one of the most common chemicals found in antibacterial hand cleaners, dishwashing liquids and other wash products. "Triclosan has a specific inhibitory target in bacteria similar to some antibiotics," says epidemiologist Allison Aiello at the University of Michigan School of Public Health.

That's pretty much to be expected, so I am interested in being surprised.

Rich said...


From here:

"An article coauthored by Dr. Stuart Levy in the August 6, 1998 issue of Nature (PMID 9707111) warned that its overuse could cause resistant strains of bacteria to develop, in much the same way that antibiotic-resistant bacterial strains are emerging, based on speculation that triclosan behaved like an antibiotic. Based on this speculation, in 2003, the Sunday Herald newspaper reported that some UK supermarkets and other retailers were considering phasing out products containing triclosan.

It has since been shown that the laboratory method used by Dr. Levy was not effective in predicting bacterial resistance for biocides like triclosan, based on work by Dr. Peter Gilbert in the UK [1] (PMID 12957932). At least seven peer-reviewed and published studies have been conducted demonstrating that triclosan is not significantly associated with bacterial resistance, including one study coauthored by Dr. Levy, published in August of 2004 in Antimicrobial Agents and Chemotherapy (PMID 15273108).

Some level of triclosan resistance can occur in some microorganisms, but the larger concern is with the potential for cross-resistance or co-resistance to other antimicrobials. Studies investigating this possibility have been limited. (PMID 16922622)"

John Paul said...

Thanks, Rich. Before Scientific American reformulated itself as a glitzy magazine, I would have expected more from the article on exactly what the specific mechanism is that might be shared with some antibiotics. I've heard before that triclosan acts more broadly against microbes so that developing resistance or cross-resistance is less likely.

When bacteria are exposed to triclosan for long periods of time, genetic mutations can arise. Some of these mutations endow the bacteria with resistance to isoniazid, an antibiotic used for treating tuberculosis, whereas other microbes can supercharge their efflux pumps—protein machines in the cell membrane that can spit out several types of antibiotics, Aiello explains. These effects have been demonstrated only in the laboratory, not in households and other real world environments, but Aiello believes that the few household studies may not have been long enough. "It's very possible that the emergence of resistant species takes quite some time to occur…; the potential is there," she says.

The article does not specifically state whether the exposure times in the article above, of three months to one year, were too short in the researcher's opinion.

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