Although this study did not aim to investigate the actual mechanisms involved in the observed changes in surface microbiota, some assumptions can be made based on existing literature. The most relevant mechanism underlying the observed effect is likely due to competitive exclusion: Bacillus strains applied on the surfaces within the cleaning solution may compete, in terms of nutrients and space, with the microbiota already present on the surfaces . Woo & Ahn have suggested that competitive exclusion can also destabilize certain biofilms , which was observed in the present study as removal of grout on certain hard surfaces after several weeks of microbial cleaning. Such biofilm removal on hard surfaces by means of microbial cleaning deserves further research. Another mechanism that is likely to contribute to
the changes in microbiota upon microbial cleaning, and also destabilize biofilm formation, is quorum sensing and quorum
quenching. The constant artificial introduction of dominant counts of Bacillus spp. through the cleaning products could
destabilize the microbial population dynamics on surfaces and in biofilm (e.g. grout). Given the observed general effect of microbial