(492a) Probiotic Escherichia coli Inhibits Biofilm Formation of Pathogens

Numerous chronic bacterial infections are involved in biofilm state and it is difficult to eradicate them by antibiotics. Biofilm formation is an inter-species phenomenon that involves dynamic interactions between bacteria in the biofilms. However, little is known to understand molecular interactions between biofilm bacteria especially in multi-species biofilms while majority biofilm studies has been done in mono-species. Escherichia coli strain Nissle 1917 (EcN) is a probiotic bacterium that has antagonistic effects on adherence, growth, and biofilm formation of other E. coli strains. In this study, we investigated the ability of EcN to outcompete with the biofilm formation of diverse pathogens such as enterohemorrhagic E. coli (EHEC), Enterococcus faecalis, Pseudomonas aeruginosa, and Serratia marcescens. When dual-species biofilms are formed, EcN reduced EHEC biofilm population up to 100-fold compared to EHEC mono-species biofilm formation, E. faecalis 10-fold, and P. aeruginosa 10-fold. EcN was dominant in the dual-species biofilms by occupying up to 90% of the total biofilm population. To see whether the molecules secreted from EcN affect EHEC biofilm formation, we grew EHEC biofilms under EcN cell-free supernant. EcN-supernatant inhibited EHEC biofilms up to 100-fold which is similar level of reduction to the result of EcN-EHEC biofilms. As a control, non-probiotic and non-pathogenic E. coli BW25113 did not reduce the biofilm formation of pathogenic bacteria. These results imply that probiotic E. coli inhibits the biofilm population of pathogenic bacteria, and provide insights that probiotics can be applied as an effective treatment for the biofilm-related infectious diseases.