Escherichia coli Nissle 1917 forms biofilm and outgrows Escherichia coli K12 in a temperature-dependent manner

Planktonic Escherichia coli may grow as biofilms adhered to a surface when environmental stressors are detected. Previous studies utilizing co-culture (culturing of two or more cell populations in contact with one another) and dual-species biofilm-based methods have found that probiotic E. coli Nissle 1917 (EcN) may inhibit biofilm formation of other E. coli strains and outcompete their growth. However, the exact mechanism of biofilm inhibition has yet to be elucidated. Using the EcN and E. coli K12 MG1655 (K12) strains, we investigated biofilm inhibition using a biofilm quantification assay. Growth curves for EcN and K12 were compared at 30°C and 37°C. Subsequently, biofilm formation assays were performed according to a previously established protocol at 30°C and 37°C. Growth curve analysis showed two exponential growth phases for EcN at 30°C (n=3), with the strain reaching a higher final OD600 compared to K12. At 37°C, K12 underwent two
exponential growth phases, and the strains grew to similar OD600 values after 24 h. Consistent with the growth curves, EcN formed significantly more biofilm than K12 at 30°C (p=0.0012). Neither strain formed quantifiable biofilm at 37°C. Given higher rates of biofilm formation in EcN than K12, we infer that in co-culture, the majority of the biofilm quantified would consist of EcN rather than K12. Our current protocol appears unsuited for assaying biofilm inhibition in co-cultures. Future studies may instead use supernatant-based assay methods to determine whether EcN secretions affect K12 biofilm formation.