Triclosan, a common antimicrobial agent, may be changing gut biomes

Lathering up with hand soap or sanitizer may kill 99.9 percent of surface bacteria, but these antibiotics may be affecting much more than just skin—they may be affecting bacteria in the gut.

Oregon State University researchers took the first step in determining what repercussions antimicrobials could potentially have on human health.

Publishing their findings in PLOS ONE, a website at which researchers can publish work for peer review, OSU researchers determined triclosan, a common antimicrobial agent, can disrupt bacteria found in the gut of zebrafish, and may possibly affect humans as well.

Triclosan, first used as a hospital scrub in the 1970s, is now one of the most common antimicrobial agents in the world. It is found in products ranging from shampoos, hand soaps and toothpastes to cutting boards, trash bags and athletic clothing.

Although triclosan works to rid harmful bacteria in the bacterial communities found in the gut, called the microbiome, it may have adverse effects on human health, according to Assistant Professor of Microbiology and Statistics Thomas Sharpton.

“The antimicrobial drugs that we are exposed to every day can be useful because they eliminate microorganisms that create infections, but they also are indiscriminate,” Sharpton said. “They might eliminate microorganisms that we need, which can have an unpredictable effect on our health.”

OSU researchers were prompted to study the effects triclosan has on the microbiome due to speculation of the correlation between altered microbiomes and disease, according to Sharpton.

“We were captivated by the growing literature that was indicating that an alteration of the microbiome appears to be strongly associated with, or even responsible for, chronic diseases, such as obesity, diabetes and heart issues,” Sharpton said.

The OSU researchers used 45 zebrafish to determine if repeated exposure to triclosan alters the microbiome of the fish. The researchers chose triclosan due to its frequent contact with humans, and the zebrafish due to their biochemical similarities to humans.

After four to seven days of treating the zebrafish with high concentrations of triclosan, the researchers discovered the speculation of the effects antimicrobials have on microbiomes proved correct, according to Christopher Gaulke, postdoctoral scholar and lead author of the study.

“The microbiomes in the triclosan fish were different, not only in the types of bacteria but also the quantity,” said Gaulke. “Our study provided proof of the concept that triclosan is capable of disrupting the microbiome.”

Proving triclosan’s alteration of the microbiome may be the first step in determining if there is a link between disrupted microbiomes and chronic diseases, according to Robert Tanguay, professor in the department of environmental and molecular toxicology.

“It is possible that some diseases could actually be directly caused by the effects of environmental chemical contaminants on the microbiome,” Tanguay said. “We are now well positioned to investigate this because of the advantages of the zebrafish model and zebrafish facility.”

Although the direct effect of an altered microbiome on human health is still unclear, the study’s proof of the effects of triclosan opens the doors to studies with new chemicals, according to Tanguay.

“Now that we know environmental chemicals can alter the gut microbiome, we can now look at other common environmental chemicals to see if they impact the gut microbiome and or impact health,” Tanguay said.

Although this pilot study has not proven the effects of microbiome alteration on human health, the use of zebrafish provides a method of screening intoxicants in the future, according to Gaulke.

“One of the problems researchers have is humans are exposed to thousands of chemicals every day, so how do we know which ones to study?” Gaulke said. “One of the undervalued successes of this study is we showed that zebrafish can be used to rapidly and effectively screen environmental intoxicants.”

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