Studies on the pathogenic role of curli in avian pathogenic E. coli infections have also been carried out, and there is evidence that haemagglutination activity, fibronectin binding and curli production are co-expressed in an APEC strain and haemagglutination and fibronectin binding are recognized as virulence factors that may be important in the adherence of pathogens to host surfaces [55]. This evidence concerns the gene FN1 and infection.