Flat-bottomed microtiter plate was coated with (100 μL/well) whole bacterial cells. The bacteria were earlier harvested from overnight liquid culture, washed thrice with 0.15 mol/L NaCl solution and adjusted to 3 × 106 CFU in 0.05 M carbonate bicarbonate buffer (pH 9.6). The plate was incubated overnight at 4 °C, washed thrice with PBS containing 0.05% (v/v) Tween 20 (PBS-T).