Biofilm formation, production of cellulose and curli fimbriae in Escherichia coli strains isolated during edema disease of swine

Edema disease (ED), caused by Escherichia coli has a huge economic impact on swine breeding. The capability to colonize hosts and survive in the environment is linked to biofilm formation. Biofilm is defined as a structured community of bacterial cells enclosed in a self-produced polymer matrix that is attached to a surface. Bacteria within biofilms can withstand host immune responses, and are much less susceptible to antibiotics and to disinfectants when compared with their planktonic counterparts. Many bacterial surface structures, including curli, flagella, pili and exopolysaccharide, play a role in various aspects of biofilm development. In this study we have examined the biofilm formation in 65 E. coli field strains, isolated from ED affected pigs. Using phenotypic assays, curli fimbriae and cellulose, two extracellular structures contributing to biofilm formation were investigated. Results showed that 23% of the strains were classified as strong biofilm producers while 71% were regarded as weak biofilm producers. All the O-138 serotypes were weak producers, while the majority (73%) of the O-139 types were strong biofilm producer strains. Moreover, there is a different expression of both the studied structures, at the two tested temperatures. Noteworthy, 75% of the E. coli strains isolated during episodes of ED produced curli fimbriae at 37 degrees C. A significant association has been observed between the O-type and the production of the biofilm and a significant difference in the morphotype results was observed on the basis of the used temperature. Our observations reveal E. coli from ED are biofilm formers, with different expression of the both studied structures, which may be linked to a role in virulence.