Case report: contamination of a drinking water distribution system by <i>Exophiala</i>-dominated biofilm in the Midwestern United States

Fungal contamination of drinking water distribution systems can impact water quality with implications for public health. We document an instance of <i>Exophiala</i> spp. biofilm contamination of customer taps in the Midwest United States following consumer complaints. Three samples of black biofilm were collected from customer taps in Ohio and then processed using next-generation DNA sequencing of the bacterial 16S and fungal ITS regions. Two samples with successful ITS sequencing were dominated by <i>Exophiala</i> spp., putatively identified as <i>E. cancerae</i> and <i>E. lecanii-corni</i>. Dominant bacterial phyla in samples included Proteobacteria, Bacteroidetes, Actinobacteria, and Acidobacteria. Bacterial composition varied substantially at the family and genus levels, and potentially pathogenic bacteria (i.e., <i>Acinetobacter</i> spp., <i>Legionella</i> spp., <i>Mycobacterium</i> spp., and <i>Pseudomonas</i> spp.) were detected. The potential for fungal contamination of drinking water distribution systems should be evaluated when biofilms are observed.