Opportunistic pathogens enriched in showerhead biofilms

Abstract

The environments we humans encounter daily are sources of exposure to diverse microbial communities, some of potential concern to human health. In this study, we used culture-independent technology to investigate the microbial composition of biofilms inside showerheads as ecological assemblages in the human indoor environment. Showers are an important interface for human interaction with microbes through inhalation of aerosols, and showerhead waters have been implicated in disease. Although opportunistic pathogens commonly are cultured from shower facilities, there is little knowledge of either their prevalence or the nature of other microorganisms that may be delivered during shower usage. To determine the composition of showerhead biofilms and waters, we analyzed rRNA gene sequences from 45 showerhead sites around the United States. We find that variable and complex, but specific, microbial assemblages occur inside showerheads. Particularly striking was the finding that sequences representative of non-tuberculous mycobacteria (NTM) and other opportunistic human pathogens are enriched to high levels in many showerhead biofilms, >100-fold above background water contents. We conclude that showerheads may present a significant potential exposure to aerosolized microbes, including documented opportunistic pathogens. The health risk associated with showerhead microbiota needs investigation in persons with compromised immune or pulmonary systems.

Fig. 1.

Fluorescence and SEM images of showerhead biofilm. (A–C) Epifluorescence microscopy of biofilm samples stained with DAPI; scale bars, 10 μm. (D–F) SEM micrographs of increasing magnification of in situ showerhead biofilm on the inner surface of one water distributor (Scale bars, 2 μm.)

Fig. 2.

This heatmap-table summarizes the BLAST results for all showerhead swab libraries, pooled at the genus-level and grouped by municipality of origin. Genera representative by at least 0.5% of the total clones (>20 sequences) were included, for a total of 17 genera. Figure footnotes: *, “Other” is comprised of all genera representing less than 0.5% of total dataset; †, percent of total showerhead clones in study; ‡, showerhead fed by well water; §, signifies the first of multiple samples taken at the site as designated by the first three letters; ¶, signifies the second of multiple samples taken at the site; ‖, signifies the third of multiple samples taken at the site; −, signifies that clones representative of the genera were not detected in the sample.

Fig. 3.

Comparison of the diversity of abundant sequences from swab biofilm and water samples collected from sites supplied by treated municipal water, private well water supplied sites were excluded from this analysis. (A) A comparative histogram of the most abundant swab and water genera identified by BLAST. The total number of sequences for municipal biofilms was n = 3,454, for municipal water n = 1,146. (B) Pie chart of mycobacterial sequences (n = 1,051) identified in showerhead biofilm samples. (C) Pie chart of mycobacterial sequences (n = 131) from water samples.