Production of exopolysaccharide and curli by enterohemorrhagic Escherichia coli O157:H7 as affected by temperature, pH, and nutrient availability, and its influence on attachment, biofilm formation, and resistance to chlorine
MetadataShow full item record
Production of exopolysaccharide (EPS) and curli by enterohemorrhagic Escherichia coli O157:H7 under various environmental conditions was characterized and the roles of EPS and curli on attachment to and biofilm formation by E. coli O157:H7 on stainless steel were studied. Subsequent resistance of cells to treatment with chlorine was investigated. To quantify the amount of EPS produced by E. coli O157:H7, the concept of extracellular carbohydrate complexes (ECC) was coined and a standard method for quantification of ECC was developed. Using this method, the influence of environmental conditions on cell growth, the total amount of ECC produced, and the amount of ECC produced on a per cell biomass basis by E. coli O157:H7 was determined. Conditions favorable for the production of ECC, on a per biomass basis, were lower nutrient availability, lower temperature (12oC vs. 22oC), lower pH (5.0 vs. 7.0), and aerobic atmosphere. Modified atmosphere (1% O2, 10% CO2, and 89% N2) inhibits cell growth and ECC production. Production of EPS and curli as influenced by nutrient availability and temperature, on attachment and biofilm formation by E. coli O157:H7 on stainless steel coupons (SSC) was investigated. Production of EPS by E. coli O157:H7 inhibits attachment of cells on SSC but it does not affect cell growth during biofilm formation. Production of curli by E. coli O157:H7 does not affect attachment of cells on SSC but curli-producing strains are better able to form biofilms. Cell suspensions and biofilms produced by E. coli O157:H7 strains 43895-EPS (EPS producing mutant), ATCC 43895-, and ATCC 43895+ (curli-producing mutant) were compared for their resistance to treatment with chlorine at concentrations used to sanitize food processing equipment. Resistance of E. coli O157:H7 to chlorine increased significantly as cells formed biofilm on SSC. Production of EPS and curli by E. coli O157:H7 significantly increased the resistance of cells in biofilm against chlorine. These results provide fundamental information of value when developing intervention strategies to control biofilm production and to kill E. coli O157:H7 in biofilms that have formed on food contact surfaces and foods.