Bathing in Bacteria: Mycobacteria Relative Abundance on Showerhead Biofilms

Mycobacterium is a genus of Actinobacteria that contains many human pathogens, causing diseases such as tuberculosis, leprosy, and nontuberculous mycobacteria (NTM) lung disease. Diagnosed cases of NTM lung disease, are increasing rapidly across the United States. Recent studies have indicated that this respiratory infection is acquired through the inhalation of aerosolized mycobacteria derived from the biofilms found on the inside of household showerheads. To asses the factors that influence mycobacteria abundance on the interior biofilms of showerheads we analyzed bacterial and protistan communities from showerhead samples gathered across the United States. Further, we investigated water chemistry, specifically total chorine concentration and pH, and geographical variables to better understand the factors influencing the relative abundance of mycobacteria. After analyzing 191 samples, we found that Mycobacterium was the most common genus in showerhead biofilms, with a mean relative abundance of 19.2%. We found that mycobacteria were more abundant in biofilms with water sourced from municipal water than from well-water. This could be due to the higher chlorine content of municipal water, as mycobacteria are known to have mechanisms to resist chlorine. This is corroborated by the fact that mycobacteria were more abundant in samples with higher total chlorine concentrations. Mycobacterial abundances were not influenced by the pH of the water, the geographical location of the sample, or the relative abundance of free-living amoebas (FLA). Our results indicate that showerhead biofilms from chlorinated, municipal water supplies are more likely to contain mycobacteria. This indicates that individuals using these ii showers may be at a higher risk of developing NTM lung disease and that the addition of chlorine to household water may be linked to the increasing incidence of this disease