After incubation (3, 48 and 72 h) wells were washed twice with PBS and stained with 100 µL of 0.4% aqueous crystal violet solution for 45 min. Afterwards, wells were washed four times with sterile distilled water (SDW), and immediately destained with 200 µL of 95% ethanol. After 45 min, 100 µL of destaining solution was transferred to a new polystyrene 96-well plate and the amount of crystal violet in the solution was measured at 590 nm. The absorbance values for the controls were subtracted from the values for the test well to minimize background interference.