High resolution ITS amplicon melting analysis as a tool to analyse microbial communities of household biofilms in ex-situ models.

Biofilms are the most common growth types of microorganisms. These complex communities usually consist of different species and are embedded in an extracellular matrix containing polymers, proteins and DNA. This matrix offers protection against different (a)biotic environmental factors and generally increases resistances. Higher resistances against antibiotics are one of the main reasons why biofilms are often associated with healthcare settings. Nevertheless, they are also found in domestic settings, mostly in humid places with abundant nutrients like dishwashers or washing machines. Biofilms in these areas show individual compositions and are influenced for example by temperature, frequency of use or the age of the device. In this study, we introduce a model for the ex-situ cultivation of domestic biofilms from household appliances. Furthermore, we tested the ability of high resolution melting analysis (HRMA) as a tool for analysing these biofilms. Our goal was to maintain a high amount of complexity in the ex-situ biofilms that is characterized by the melting behavior of the contained DNA. Dishwasher and washing machine biofilms were sampled in private households and cultivated for 10 d. After DNA extraction, 16S rDNA was sequenced and melting behavior of the bacterial Internal Transcribed Spacer (ITS) region was analysed. Additionally, testing for independence of continuous new sampling, storage of cultivated biofilms in glycerol stocks and following recultivation of them was done up to three times. Our results show that a high level of complexity could be maintained in the ex-situ biofilms after 10 d of cultivation, although in general the bacterial diversity slightly decreased compared to the original biofilm in most cases. Recultivation of a similar biofilm from glycerol stocks was possible as well with some impact by various factors. Differences in the bacterial composition of biofilms could clearly made visible by HRMA although it was not possible to match peaks to a specific phylogenetic group. Still, HRMA proved to be a less costly and time consuming alternative to sequencing for the characterization of biofilms.

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Declaration of Competing Interest The authors declare no conflict of interest.