Sometimes an impending train wreck is obvious, made even worse as it unfolds in slow motion, and particularly painful when it seems preventable. And so it is every time we wash our hands or even put on our socks maybe we should listen for a far-off whistle....
Last month, in an extensive report on illness and death linked to antibiotic-resistant “superbugs,” the Centers for Disease Control and Prevention sounded the alarm (again): Hospitals over-prescribe antibiotics and too many farms routinely dose livestock to stimulate growth. When genetically mobile, rapidly reproducing creatures such as bacteria collide with frequently used drugs, they inevitably develop resistance. The solution is (theoretically) simple: Don’t prescribe antibiotics unless they’re clearly necessary. Slowing down the evolutionary train will give scientists time to come to the rescue with new medicines. Failing to do so will mean even more untreatable infections and more unnecessary deaths.
But the CDC might have missed a Mack truck heading for the tracks. A few days after the release of their report, a much smaller study published in the journal Environmental Science and Technology reported that triclosan, the chemical used in antibacterial soap, substantially increases triclosan-resistant bacteria in waterways downstream from cities and suburbs.
Given the dubious need for antibacterial soap in the first place, the antibiotic overreach of prescription happy doctors and the profusion of prophylactic use by big agribusiness, do we really want to create another superfluous path for superbugs?
Antibacterial soap is ubiquitous these days. By some estimates, 75 percent of liquid hand soap contains triclosan or other antibacterial compounds. Dishwashing detergent, body washes, lotions, toothpaste, socks, toys, cutting boards, and other personal products often also contain antibacterials, a marketing response to consumer fears about germs. But a U.S. Food and Drug Administration advisory panel concluded in 2005 that antibacterial soap is no more effective than plain old soap and water at removing germs. Some scientists think it does more harm than good.
Past laboratory studies have found that bacteria resistant to triclosan, including strains of Salmonella and E. coli, often are resistant to common antibiotics as well (perhaps not a big surprise for creatures that can swap DNA). Here’s a key mechanism for resistance: Proteins on cell membranes called efflux pumps shuttle harmful substances like triclosan and antibiotics out of bacteria, leaving bacterial cells functioning just fine. These pumps might be specific to certain substances, or be more general and work with many different kinds of substances. Other processes can confer resistance as well, but efflux pumps are particularly powerful: Their genes are encoded on snippets of DNA that bacteria share freely with one another.
The most recent research examined triclosan not just in the laboratory, but in the environment. When Bradley Drury of Loyola University and his colleagues measured triclosan concentrations in river sediment at six sites outside of Chicago, they found a clear pattern: Urban sites had greater concentrations than suburban sites, which in turn had greater concentrations than woodland sites. Both of the urban sites were located downstream from sewers that overflow during heavy rains and thus feed soapy wastewater from sinks and showers—plus, of course, raw sewage from toilets—directly into the river. When researchers looked at the proportion of triclosan-resistant bacteria at each site they found the same pattern: High concentrations of triclosan meant a greater percentage of triclosan-resistant bacteria in the microbial mix. They backed up their field findings with a controlled experiment in the lab to make sure what they were seeing was caused by triclosan: When they added triclosan to artificial streams in the lab, they generated triclosan-resistant bacteria. When they left artificial streams alone, they didn’t.
Which raises the question: Given the dubious need for antibacterial soap in the first place, the antibiotic overreach of prescription-happy doctors and the profusion of prophylactic use by big agribusiness, do we really want to create another superfluous path for superbugs?
Attorneys at the Natural Resources Defense Council say no. They’ve sued the FDA to regulate triclosan under the Federal Food, Drug and Cosmetic Act, a task that has been on the FDA to-do list for 36 years. In 1994, the FDA announced that it needed more evidence to determine whether triclosan was safe and effective. Since then, antibacterial products have proliferated and triclosan has become pervasive. In 2009, the CDC reported triclosan in the urine of 75 percent of Americans. The Environmental Protection Agency found it in 92 percent of sewage sludge samples.
The NRDC argues that, in addition to promoting antibiotic resistance, triclosan poses health risks as an endocrine disruptor. It cites scientific studies demonstrating that triclosan, interferes with sex hormones—including testosterone and other hormones related to sperm production—and thyroid function in lab animals. The American Cleaning Institute, a trade association representing the U.S. cleaning products industry, maintains that triclosan doesn’t cause endocrine disruption or antibiotic resistance at levels found in the environment. This spring, a U.S. Appeals Court allowed the NRDC’s suit to proceed but only the portion related to triclosan, not the portion related to a sister antibacterial (and suspected endocrine disruptor) often used in bar soaps called triclocarban. The FDA has said its review of triclosan is now a top priority. “Hopefully scientific evidence since ’94 will point FDA in the right direction to say that triclosan is not safe and effective,” said Mae Wu, program attorney for NRDC. But she acknowledges that an actual decision could still be years away.
In the meantime, some companies are proceeding on their own. Kaiser Permanente removed triclosan from its hospitals in 2010. Proctor and Gamble and Johnson and Johnson both announced they will eliminate triclosan from their products in coming years, maintaining that, although they believe triclosan is safe, they want to ease customer fears. Colgate-Palmolive removed triclosan from its popular hand soap, but replaced it with another antibacterial compound (benzalkonium chloride) that’s also in FDA limbo. It’s unclear whether other manufacturers will simply swap triclosan for a different set of questionable chemicals as well.
Moreover, triclosan persists in the environment long after it’s introduced. The Loyola team found the abundance of resistant bacteria in artificial streams continued to climb for weeks after just one dose of triclosan. After five weeks, they stopped counting. Last month’s CDC report flagged hospitals as the primary source of antibiotic-resistant superbugs. Next time, it could be your powder room.