Biofilm formation ability and tolerance to food-associated stresses among ESBL-producing Escherichia coli strains from foods of animal origin and human patients

The dissemination of extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli continues to be an important health concern, with the food production chain as a suggested reservoir. A collection of 31 strains, including ESBL-producing E. coli strains isolated from foods of animal origin and from human patients and reference collection strains, was evaluated regarding their biofilm formation ability, tolerance to food-associated stresses (heat, acid, non-thermal atmospheric plasma (NTAP) and UV-C light) and RpoS status. The most relevant phenotypic differences among strains were observed for biofilm formation and heat resistance, being related to the source of isolation (clinical vs food vs reference) or to the sequence type (ST131 vs other STs), while only minor differences were related to the occurrence of the ESBL genes (bla(TEM), bla(CTX-M), bla(SHV)). The biofilm formation ability on stainless steel was significantly higher for the field isolates, both clinical- and food-related, than for the reference strains. Food isolates were more thermotolerant (58 degrees C-1 and 2 min) than clinical isolates. Minor differences among strain categories were observed for their tolerance to the other inactivation technologies. Some polymorphisms in the rpoS gene sequences were detected, but loss-of-function mutations were not found, with the clustering of strains mainly based on their sequence type.