Bacteriome of Washing machines

Background: Washing machines are central hygiene tools in domestic environments. Facilitated by recent washing trends (low temperature washing, bleach-free liquid detergents), microorgan-isms find optimal living conditions here: humidity, warmth, nutrients and rarely cleaned surfaces [1]. The microbiota in washing machines causes staining, corrosion, machine and laundry malo-dor, and might thus negatively affect laundry hygiene [2,3]. We investigated the bacterial micro-biota in domestic washing machines and the influence of environmental factors on its composi-tion.Methods & Results: The bacterial microbiota of 21 in-use domestic washing machines was sampled at different sites (detergent drawer, door seal, sump, and washing solution) and ana-lyzed by 16S rRNA gene pyrosequencing. Over all samples, 26 phyla, 583 genera and 7161 species OTUs were detected. Proteobacteria (86.0%), Actinobacteria (5.4%), Firmicutes (3.0 %) and Bacteroidetes (2.8%) were the dominant phyla. At genus level, Pseudomonas, Acinetobacter and Moraxella were relatively most abundant, the latter of which are known to comprise well-known malodour producers. Correlation analysis with data from a user survey revealed “sam-pling site” and “monthly number of high temperature washes” to significantly affect microbial diversity. The highest diversity was determined for the detergent drawer on all taxonomic levels, followed by sump, washing solution and door seal. Microbial diversity also increased with an increasing number of wash cycles per month at ?60°C.Conclusion: Domestic washing machines are characterized by a diverse and site-dependent bac-terial microbiota, which appears also to be influenced by the washing temperature. Our data will help to better understand the hygienic relevance of the washing microbiota and to develop tar-geted hygiene strategies to further improve laundry hygiene [1] Egert, M. (2017). SOFW Journal 143, 4: 44–48; [2] Callewaert C. et al. (2015). Front. Mi-crobiol. 6., DOI: 10.3389/fmicb.2015.01381; [3] Nix I. et al. (2015). Tenside Surfactants Deterg 52: 432–440