Molecular and phenotype characterisation of persistent Escherichia coli in dairy products from Midwest Brazil

Background Biofilm‐forming Escherichia coli , carrying genes for the transmissible locus of stress tolerance (tLST) and pathogenicity genes, pose a risk to public health and dairy production. Aim To evaluate the phenotypic and molecular characteristics of E. coli strains isolated from two segments of the dairy supply chain: inspected milk and raw milk and dairy products without official inspection. Methods Classical methods were used to identify and characterise 77 E. coli strains isolated from 98 milk and dairy product samples in Midwest Brazil regarding biofilm formation, curli protein and motility. In addition, molecular methods were used to investigate pathogenicity genes ( eaeA , ehxA , stx1 , and stx 2), heat resistance, and stress resistance (tLST and rpoS ). Major Findings Through the yaiO gene, 75 strains were identified as E. coli , 39 from refrigeration tanks and 36 from raw milk and dairy products. Of these strains, 26.67% (20/75) were positive for the eaeA gene and 4% (3/75) for the ehxA gene. Regarding the genes to biofilm formation ( rpoS ) and stress tolerance (tLST), amplification was detected in nine and six strains, respectively. The 20 strains carrying the eaeA gene were classified as enteropathogenic E. coli (EPEC). All strains were phenotypically positive in the motility test; 98.67% were classified to produce weak, moderate, strong, very strong and extremely strong biofilm intensities. In addition, curli protein expression was detected in 49.33% of the E. coli strains. Scientific Implications The ability of E. coli strains isolated from products originating from two distinct segments of the dairy sector to produce biofilms, carry genes for resistance to thermal stress and pathogenicity, suggests strong persistence in these environments, as well as indicating a potential risk to public health.