Thursday, September 26, 2013
Triclosan, a compound common in soaps, detergents, and even plastics, is designed to kill bacteria, but it may also be driving the development of antibiotic-resistant bacteria in rivers and streams. This finding, published earlier this summer in Environmental Science & Technology, is just the latest in a growing list showing that high concentrations of triclosan change the mixture of species in bacterial communities, interfere with hormone systems in fish, and is lethal to the algae that form the base of the food web.
Researchers identified the connection between triclosan concentrations and resistant bacterial communities during a combined field and lab study designed to investigate the impact of the antibacterial on bacteria on the riverbed. From a series of samples taken from three Chicago-area rivers, researchers found two significant correlations: triclosan concentrations and the proportion of bottom-dwelling bacteria that are resistant to it both increase with urbanization. The woodland creek tested had the lowest levels of resistant bacteria, while the urban river had the highest. And artificial stream experiments conducted at Loyola University Chicago later confirmed the finding that exposure to high concentrations of triclosan triggers resistance.
There are numerous ways a bacterial community can develop resistance, and it is still unclear which mechanisms are behind freshwater bacteria's resistance to triclosan. Results of the artificial stream study, though, suggest that exposure to triclosan actually favors bacterial species already resistant to the compound, leaving them to thrive while more sensitive species die out. The result is a less diverse bacterial community made up of species that can withstand high concentrations of triclosan.
This shift in species composition could have significant impacts on the overall health of aquatic ecosystems. Different species of bacteria play different roles–everything from producing oxygen to breaking down leaves and branches that fall in the water. Change the mix of bacteria, and aquatic life higher up the food chain could be left without the nutrients they need to survive. And because some bacteria are toxic to plankton, fish, and other wildlife, changing the makeup of a bacterial community may prove fatal.
Increased resistance may also affect human health. According to the researches, triclosan-resistant bacteria are commonly resistant to other antibiotics, ones we use to treat diseases. Rising concentrations of triclosan in water, then, may increase the number of pathogens that can withstand the antibiotics we currently rely on to kill them.
Drury, B., Scott, J., Rosi-Marshall, E.J., and Kelly, J.J. 2013. Triclosan exposure increases resistance and influences taxonomic composition of benthic bacterial communities. Environmental Science and Technology 47:8923-8930.