Biofilm Formation Potential of Heat Resistant Escherichia coli Dairy Isolates and Complete Genome of MDR Heat Resistant Strain FAM21845
We tested the biofilm formation potential of 30 heat resistant and six heat sensitive E. coli dairy isolates. The production of curli and cellulose, static biofilm formation on polystyrene (PS) and stainless steel, formation of biofilm under dynamic conditions (Bioflux), and initial adhesion rates (IAR) were evaluated. Biofilm formation varied greatly between strains, media and assay. Our results highlight the importance of the experimental setup to determine biofilm formation under conditions of interest, as correlation between different assays was often not given. The heat resistant, multidrug resistant (MDR) strain FAM21845 showed the strongest biofilm formation on PS, highest IAR, and was the only one forming significant biofilm on stainless steel under dairy industry relevant conditions and was therefore fully sequenced. Its chromosome is 4.9 Mb in size and it harbors a total of five plasmids (147.2, 54.2, 5.8, 2.5, and 1.9 kb). The strain encodes a broad range of antimicrobial resistance and biofilm relevant genes, some on its two large conjugative plasmids, as demonstrated in plate mating assays.Importance In biofilms, cells are embedded in an extracellular matrix that protects them from stresses like UV radiation, osmotic shock, desiccation, antibiotics and predation. Biofilm formation is a major bacterial persistence factor of great concern to the clinic and food industry. Many tested strains formed strong biofilm and especially strains like the heat resistant, MDR FAM21845 may pose a serious issue for food production. Strong biofilm formation, combined with diverse resistances (some on conjugative plasmids), may allow for increased persistence, co-selection and possible transfer of these resistance factors. Horizontal gene transfer could conceivably occur in the food production setting or the gastrointestinal tract after consumption.