This organic compound is a white powdered solid with a slight aromatic/phenolic odor. It is a chlorinated aromatic compound which has functional groups representative of both ethers and phenols. Phenols often show anti-bacterial properties. Triclosan is slightly soluble in water, but soluble in ethanol, diethyl ether, and stronger basic solutions such as 1 M sodium hydroxide, like many other phenols.

Uses

It is found in soaps, deodorants, toothpastes and is impregnated in an increasing number of consumer products, such as kitchen utensils, toys, bedding, socks, and trash bags. It has been shown to be effective in reducing and controlling bacterial contamination on the hands and on treated products.

Triclosan is regulated by both the U.S. Food and Drug Administration and by the European Union. In the environment, triclosan is removed during normal waste treatment processes as shown by extensive environmental studies, and any of it that remains after waste treatment quickly breaks down into other compounds in the environment. However, one study showed that triclosan was broken down into dioxins in river water, because of the presence of sunlight (PMID 15779749).

Mechanism of action

Triclosan appears to kill bacteria mainly by inhibiting fatty acid synthesis. Triclosan binds to bacterial enoyl-acyl carrier protein reductase (encoded by FabI) and increases the enzyme's affinity for nicotinamide adenine dinucleotide (NAD⁺). This results in the formation of a stable ternary complex of FabI-NAD⁺-triclosan, which is unable to participate in fatty acid synthesis. Some bacterial strains are resistant to triclosan due to FabI mutations which decrease triclosan's effect on FabI-NAD⁺ binding. (PMID 10196195) Another way for bacteria to gain resistance to triclosan is to overexpress FabI (PMID 11418506).

Resistance concerns

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 (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). In addition, there is 30 years of experience with triclosan without any incidences of acquired bacterial resistance reported, and there are no studies showing acquired resistance after long-term use.

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Popularity of germ fighter raises concern - triclosan - Brief Article
From Science News, 5/27/00 by J. Travis

Deodorants, mouthwashes, toothpastes, soaps, cutting boards, baby toys, high chairs, and carpeting. Even sweat-socks, underwear, and hunting clothes. On her visits to the local Wal-Mart, Maura J. Meade of Allegheny College in Meadville, Pa., found examples of those products and others that incorporate the bacteria-killing agent triclosan. "It's all over the place," she says.

That pervasiveness may carry a price, Meade and two other investigators warned at this week's American Society for Microbiology meeting in Los Angeles. Each reported studies on triclosan-resistant microbes and expressed concern that the antiseptic's increasing popularity will encourage the evolution of bacteria impervious to drugs. For the moment, however, that worry remains theoretical, the scientists acknowledge.

"We may compromise the effectiveness of still-useful antibiotics," says Herbert P. Schweizer of Colorado State University in Fort Collins. "I don't want to ring the alarm bell too loudly, but I do think we have to start ringing it."

Easily incorporated into liquids, fabrics, and solid surfaces, triclosan's use has soared since its introduction about 3 decades ago. Scientists once believed that bacteria can't develop resistance to triclosan because it acts more as a grenade than as a bullet. They thought the antiseptic killed bacteria in multiple ways rather than targeting a single protein, the modus operandi of most antibiotics.

In the past few years, however, biologists have discovered that triclosan's main method of killing is very specific. It inhibits an enzyme involved in fatty acid synthesis. They've also shown that some bacteria with mutations in that enzyme's gene can resist triclosan. More troubling, an antibiotic commonly employed against the tuberculosis bacterium targets the same enzyme, raising the possibility that triclosan use will lead to new drug-resistant strains of the microbe.

In his study, Schweizer focused on a second way that bacteria fend off triclosan. He found that almost all strains of Pseudomonas aeruginosa, a deadly microbe that often strikes people with weak immune systems, thwart triclosan because of the action of so-called efflux pumps. The pumps remove the antiseptic and other toxic substances from the bacteria.

When Schweizer mutated the gene for one key pump, the bacteria quickly regained their triclosan defense by increasing production of other efflux pumps. Since the pumps also rid bacteria of many antibiotics (SN: 2/12/00, p. 110), he worries that triclosan's ubiquity will promote the evolution of microbes with multiple-drug resistance.

Peter Gilbert of the University of Manchester in England questions the way that manufacturers use triclosan in products such as cutting boards. His study found that hard surfaces impregnated with the compound slowly release triclosan. This could expose nearby bacteria to sublethal concentrations of the agent, a situation that promotes development of resistance.

To preserve the agent's effectiveness, Gilbert argues that triclosan-treated surfaces shouldn't be used unless there's a demonstrated health benefit. Few manufacturers can offer such proof, he says.

"You wouldn't want your cutting board at home to compromise the of the gloves your surgeon wears agrees Meade, noting that hospitals also use triclosan-treated clothes and gear.

Gilbert also suggests that triclosan's widespread use encourages poor hygiene. "There's a tendency to become complacent," he says.

Meade adds that overuse of triclosan will reduce the time until the agent stops working. She notes that her research group has found several strains of bacteria in nature that readily grow on the compound and one that may even use it as an energy source. Considering that bacteria frequently acquire traits from one another by exchanging genes, Meade says, triclosan's days are numbered.

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