Biofilm formation by Non-O157 Shiga toxin-producing Escherichia coli in monocultures and co-cultures with meat processing surface bacteria

Shiga toxin producing E. coli (STEC) are a significant public health concern and one of their major surviving mechanisms is biofilm formation. Published accounts are primarily on single species biofilm formation which does not reflect the complex situation in food processing plants where commensal bacteria are present. This study investigated the impact of meat processing surface bacteria (MPB) on biofilm formation by STEC, and potential links between biofilm formation by STEC and biofilm-related genes in their genomes. Biofilm formation of 6 STEC strains in mono and dual species cultures with 50 MPB strains was assessed by the crystal violet staining method, and two important extracellular substances for biofilm formation, curli and cellulose were determined using the Congo red agar method. Most MPB strains had antagonistic effects on the biofilm formation of the STEC strains. Of the genes investigated, 81% were common among the STEC strains and there seems to be a gene-redundancy in biofilm formation. Overall, biofilm formation of STEC was affected by curli-cellulose expression and companion strains. Although a plethora of genes encoding for proteins involved in essential steps in biofilm formation were present in all STEC genomes investigated; finesse of biofilm production is likely on the regulatory level, rather than the presence or absence of structural genes. Phenotypic characterization of biofilm formation under relevant conditions is then indispensable. Some MPB, particularly some members of Gram-negative aerobic bacteria, lactic acid bacteria, and Enterobacteriaceae have strong antagonistic effects on the biofilm formation by various STEC strains, which could be further explored as biocontrol agents for biofilms.