Flagellum-mediated motility has been suggested to contribute to virulence by allowing bacteria to colonize and spread to new surfaces. In Salmonella enterica and Escherichia coli species, mutants affected by their flagellar motility have shown a reduced ability to form biofilms. While it is known that some species might act as co-aggregation factors for bacterial adhesion, studies of food-related biofilms have been limited to single-species biofilms and short biofilm formation periods. To assess the contribution of flagella and flagellum-based motility to adhesion and biofilm formation, two Salmonella and E. coli mutants with different flagellar phenotypes were produced: the fliC mutants, which do not produce flagella, and the motAB mutants, which are non-motile. The ability of wild-type and mutant strains to form biofilms was compared, and their relative fitness was determined in two-species biofilms with other foodborne pathogens. Our results showed a defective and significant behavior of E. coli in initial surface colonization (p < 0.05), which delayed single-species biofilm formation. Salmonella mutants were not affected by the ability to form biofilm (p > 0.05). Regarding the effect of motility/flagellum absence on bacterial fitness, none of the mutant strains seems to have their relative fitness affected in the presence of a competing species. Although the absence of motility may eventually delay initial colonization, this study suggests that motility is not essential for biofilm formation and does not have a strong impact on bacteria's fitness when a competing species is present.
Keywords: Escherichia coli; Salmonella; biofilm formation; fliC mutants; foodborne pathogens; motA mutants.