In some Enterobacteriaceae the capability to colonize hosts and to survive in the environment is linked to the formation of biofilm, a structured community of bacterial cells enclosed in a self-produced polymer matrix which is attached to a surface (Costerton, 1995). Different bacterial surface structures (curli fimbriae, flagella, pili and exopolysaccharide) play a role in the various phases of biofilm development (Malcova et al., 2008).
193 field strains of Escherichia (E.) coli, isolated from mastitic bovine milk (n=16), from piglets affected by Edema Disease (n=65) and from rabbit with enteritis (n=112), have been studied, using phenotypic assays. The biofilm formation was tested on Congo Red Agar plates (CRA), according to Freeman et al (1989). The evaluation of the expression of both curli fimbriae and cellulose was performed as described by Hancock et al. (2007).
Biofilm production was recovered in 15/193 (7,8%) of the tested E.coli strains: 10/16 (62,5%) of the bovine and 5/65 swine strains (7,7%). No rabbit strains showed biofilm.
Curli fimbriae have been detected in 11/193 (5,7%), while 37/193 (19,2%) were cellulose-producing strains.
Biofilm formation is considered a virulence-associated trait, protecting bacteria against phagocytosis, disinfectants and antimicrobial agents. The obtained data showed a low percentage of biofilm producing strains. The expression of biofilm and of extracellular structures can be influenced by various factors, as well as phase variation and environmental conditions. In this situation, other studies must be conducted in order to know if the above mentioned structures are prone to phase variation and/ or there are different genetic expression in the E. coli strains.