Cells were collected by centrifugation at 10 000 rpm for 10 min from 1 to 5 ml samples of the culture and the pellet was re suspended in 10 ml of sodium hypochlorite reagent (pH 10.0-10.5 NaOCl content 5.25%-5.5%) according to the method recommended by Williamson and Wilkinson, (1958); Hahn, (1994) and Belal (2013a). After 1 h at 37 oC the reaction mixture was centrifuged at 5000 rpm for 10 min.