Antibacterial-Resistant Bacteria Discovered in Streams and Rivers

Bacteria are becoming harder and harder to kill as they evolve and change, adapting to new chemicals that are meant to exterminate them. Now, scientists have discovered that some bacteria in streams may be even more difficult to get rid of. It turns out that triclosan, a synthetic antibacterial used in personal care products, is fueling the development of resistant bacteria in streams and rivers.

Triclosan was first invented for surgeons in the 1960s. This particular antibacterial slows or stops the growth of bacteria, fungi and mildew. In fact, about half of liquid soaps contain the chemical in addition to toothpastes, deodorants, cosmetics, liquid cleansers and detergents. Because of this, triclosan filters into streams and rivers through domestic wastewater and other outlets.

In order to examine how triclosan was impacting the environment, researchers examined bacteria living in stream and river sediments. They looked at three sites in the Chicago metropolitan region in addition to controlled settings in a lab.

So what did they find? It turns out that increased urbanization correlated with a rise of triclosan pollution. In addition, they discovered that there were also increased levels of triclosan-resistant bacteria. Combined sewer overflows that release untreated sewage were a major source of this triclosan pollution. These overflows occur when a pipe's capacity is exceeded, typically due to excessive runoff from high rainfall or snowmelt events.

"We detected much lower levels of triclosan at a site downstream of a sewage treatment facility as compared to a site downstream of combined sewer overflows," said John Kelly, one of the researchers, in a news release. "And we demonstrated a strong link between the presence of triclosan in the environment and the development of triclosan resistant bacteria."

This is particularly worrisome. About 800 cities in the U.S. alone rely on combined sewer overflows. The EPA has already cited them as a major water pollution concern and the fact that they are contributing to triclosan-resistant bacteria makes them problem even more serious.

That's not all the researchers found, either. They also discovered that triclosan exposure is associated with a decrease of benthic bacteria and a shift in the composition of bacterial communities. In fact, there was a six-fold increase in cyanobacteria and a dramatic die-off of algae.

"Cyanobacteria are less nutritious than algae and can produce toxins," said Emma Rosi-Marshall, one of the researchers, in a news release. "In triclosan-polluted streams and rivers, changes in microbial communities could negatively affect ecological function and animal communities."

The findings are important for better understanding how pollutants can impact natural systems. In addition, it reveals that these bacteria can grow and adapt, which means that antibacterials may not be as effective in the future.

The findings are published in the journal Environmental Science & Technology.