Researchers from Northwestern University discovered distinct viral populations in household bathroom biofilms, with markedly different viral communities existing in showerheads compared with toothbrushes.
In the study, published in Frontiers in Microbiomes, the researchers analyzed 92 showerhead and 34 toothbrush metagenomes, identifying 616 high-quality viral operational taxonomic units (vOTUs), with 2 removed during analysis for a total of 614.
They found no overlap between the most abundant viruses in showerheads and toothbrushes, despite both environments receiving tap water input. Among the 614 vOTUs analyzed, 314 were detected in only one sample, and no vOTUs were shared across all 126 metagenomes.
The study identified 532 viruses associated with 32 bacterial families, with only three bacterial families—Sphingomonadaceae, Burkholderiaceae, and Caulobacteraceae—found in both environments. Notably, 44 previously uncharacterized viruses were found to target Mycobacterium species in showerhead biofilms.
The researchers reported significant correlations between bacterial and viral communities in both environments (Mantel statistics r = 0.302 for showerheads and 0.560 for toothbrushes, P = .001). Water source emerged as the sole significant predictor of viral community composition in showerheads (PERMANOVA R² = 0.026, P < .01).
Toothbrush microbiomes predominantly contained human oral-associated organisms, with Klebsiella, Streptococcus, and Veillonella identified as the top three genera. In contrast, showerhead environments featured Mycolicibacterium and Mycobacteroides, along with common soil and drinking water genera, including Sphingopyxis, Sphingobium, and Aquabacterium.
The researchers found no evidence of these viruses carrying antibiotic resistance genes or virulence factors. This findings were particularly relevant given that U.S. individuals spend 93% of their time in built environments, with 70% in their residences.
Methodologically, 75% of viral contigs were found in toothbrush samples, despite the smaller sample size compared with showerheads (34 vs 92). Geographic distribution varied, with showerhead samples collected nationwide and toothbrush samples collected within 100 miles of Northwestern University.
The authors declared having no competing interests.
