BACTERIAL COMMUNITY IN BATHROOM IN JAPAN USING NANOPORE MINION SEQUENCER

Showerheads in bathroom provide microorganisms an excellent living environment in close proximity to a critical end-user exposure route inside the building. However, little is known about the associated health risks and underlying processes of biofilm formation and its effect on water quality in shower facilities. Many Japanese people are known to take a bath for a rather long time (more than 30 min) everyday. Such a habit may cause them being exposed to microorganisms generated in the bathroom. Here, we determine and compare the bacterial composition both in showerhead feed water and showerhead biofilms aiming at the characterization of microbes and source estimation. We collected 34 water and biofilm samples in total from 18 different buildings across Japan from 2018 to 2019. The full-length 16S rRNA gene was sequenced using MinION sequencer (Oxford Nanopore Technologies). The result showed that only Methylobacterium and Sphingomonas were commonly present in all the biofilm samples. In contrast, the bacterial community in water consisted primarily of Sphingomonas, Phreatobacter, Methylobacterium, and other 10 genera related to water- associated bacteria. The community in shower water contained a significantly higher number of sequences identified as Ancylobacter, Alsobacter and other 38 genera related to soil-associated bacteria compared with those in biofilms (P<=7.0e-04). The proportion of the number of common bacteria to all those detected in the biofilm was about two times higher than those in water (P=0.0008 < 0.005). These results suggest that specific bacteria in original water would primarily adhere to the surface of showerhead where they live and grow within biofilms, never getting back to running water.