Competitive inter-species interactions underlie the increased antimicrobial tolerance in multispecies brewery biofilms

Genetic diversity often enhances the tolerance of microbial communities against antimicrobial treatment. However the sociobiology underlying this antimicrobial tolerance remains largely unexplored. Here we analyze how inter-species interactions can increase antimicrobial tolerance. We apply our approach to 17 industrially-relevant multispecies biofilm models, based on species isolated from 58 contaminating biofilms in three breweries. Sulfathiazole is used as antimicrobial agent because it shows the highest activity out of 22 biofilm inhibitors tested. Our analysis reveals that competitive interactions dominate among species within brewery biofilms. We show that antimicrobial treatment can reduce the level of competition and therefore cause a subset of species to bloom. The result is a lower percentage inhibition of these species and increased tolerance. In addition, we show that the presence of competing species can also directly enhance the inherent tolerance of microbes to antimicrobial treatment, either because species protect each other or because they induce specific tolerance phenotypes as a response to competitors (i.e. competition sensing). Overall, our study emphasizes that the dominance of competitive interactions is central to the enhanced antimicrobial tolerance of the multispecies biofilms and that the activity of antimicrobials against multispecies biofilms cannot be predicted based on their effect against mono-cultures.