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The day after Halloween, something scary may still lurk inside your showerhead. Researchers at CIRES have identified Mycobacterium as the most abundant genus of bacteria growing in the slimy "biofilm" that lines the inside of residential showerheads--and some of those bacteria can cause lung disease. In a new study, they report that mycobacteria are more prevalent in the United States than in Europe, thrive more in municipal tap water than in well water, and are especially common in geographical "hot spots" where certain types of lung disease caused by mycobacteria are also common. It's important to understand routes of mycobacterial exposure, especially in the household. We can learn a lot from studying the biofilm that accumulates inside your showerhead, and the associate water chemistry," said Matt Gebert, CIRES researcher and lead author of the new study published this week in the American Society for Microbiology's journal mBio. "There is a lot of interesting ecology at work, and it allows us to begin to understand how it can impact human health." The research team, CIRES Fellow and Professor of Ecology and Evolutionary Biology at CU Boulder Noah Fierer's group, began this work in 2017, funded partially by an CIRES Innovative Research Program grant. The team analyzed DNA collected from 656 household showers in the United States and 13 countries in Europe. Citizen scientists swabbed the inside of their showerheads with specialized kits, and mailed the "biofilm" samples to Boulder. By harnessing DNA sequencing technology, the researchers were able to identify which bacterial species that lived in showerhead slime, and how abundant they were. Mycobacteria were far more abundant in showerheads receiving municipal tap water than in those receiving well water, as well as more abundant in U.S. households versus European. https://www.eurekalert.org/pub_releases/2018-11/uoca-yss110118.php