Development of method to quantify extracellular carbohydrate complexes produced by Escherichia coli O157:H7

Aims: The aim of this study was to optimize conditions to separate extracellular carbohydrate complexes (ECC) produced by Escherichia coli O157:H7 and to standardize the amount of ECC produced on a per cell basis. Methods and Results: ECC fraction I was removed from E. coli O157:H7 cells produced on tryptic soya agar and lettuce juice agar by centrifugation. To remove ECC fraction II, cells were heated at 100°C for 10 min, then centrifuged. The sum of ECC fractions I and II was considered as the total ECC produced by E. coli O157:H7. A correlation between cell mass and turbidity (O.D. _750nm) of cell suspensions was determined. Cell mass has a linear relationship (R² = 0.93) with turbidity of cell suspensions from which ECC is removed. The amount of ECC produced on a per cell basis was calculated by dividing total amount of ECC (μg ml^-1) produced by the turbidity (O.D._750nm) of heated cell suspension after removal ECC fractions I and II. Conclusions: A method for separating ECC from cells of E. coli O157:H7 has been developed and conditions have been optimized. A standard method to estimate the amount of ECC produced on a per cell basis was also developed. Significance and Impact of the Study: Using these procedures to prepare extract of ECC from E. coli O157:H7 and to standardize values, production of ECC on a per cell basis can be estimated and a comparison of the amount of ECC produced by the pathogen grown under different environmental conditions can be accurately measured.