The working cultures were prepared by transferring 0.5 ml of the stock frozen culture to 10 ml of MRS broth and incubated for 16 hrs at 30oC. The resulting culture was transferred (2% v/v) to modified exopolysaccharide selection medium (mESM) (van den Berg et al. 1993) containing 5% (w/v) skim milk (Oxoid), 0.35% yeast extracts (Oxoid), 0.35% peptone (Difco), and 5% glucose (BDH) and incubated