CONICET | Buscador de Institutos y Recursos Humanos

Introduction Shiga toxin-producing Escherichia coli (STEC) are an important cause of foodborne illnesses worldwide. STEC strains can attach to different surface by using some adhesins. One of them is the curli fimbriae involved in biofilm formation. Locus of Adhesion and Autoaggregation (LAA) is a novel pathogenicity island carrying genes that could be involved in adhesion and biofilm formation. STEC form biofilms in different environments, which can contaminate food and generate infections, while protecting themselves against adverse conditions such as the use of disinfectants. The aims of this study were to investigate biofilm formation and curli expression by STEC LAA positives. MethodsTwo O91 strains were used, one of them is a native strain isolated from bovine and the other was a mutant with LAA deleted (named ∆LAA). The assay for quantification of biofilm formation was performed in 96-well polystyrene microtiter. Each test was performed in triplicate and in three separate experiments to 37°C for 72 h. The strains were grown in LB broth at 37°C for 18 h. During biofilm formation 0.1 ml was inoculated onto Congo Red (CR) plates at different times (0, 6, 20 h) and incubated for 48 h at 28°C. Curli-expressing strains showed red colonies and non-curli-expressing strains displayed white colonies.ResultsThe two strains were classified as strong biofilm formers, but in O91 ∆LAA the biofilm formation was reduced. In strain O91 ∆LAA the expression of curli fimbriae was uniform during the biofirm formation (at 0, 6, 20 h), while in O91 native the expression was register to 6 hour of the biofilm formation and then curli was not expressed. ConclusionsBiofilm formation could be affected in a complex way by both physiological and environmental factors. In this case the absence of LAA reduces STEC capacity to produce biofilm and it could be regulated by interaction of curli and other genes codified by LAA.