Bacterial cell suspensions were prepared by streaking the isolates onto tryptic soy agar and incubating at 27 °C for 24 h to check the purity, then transferring single colonies onto tryptic soy agar plates. After 24 h, the bacterial cells were harvested from plates in sterile distilled water and centrifuged at 8000g for 5 min (REMI C-24, Bangalore, India). The pellets obtained were resuspended in sterile distilled water and again subjected to centrifugation, and the supernatants were discarded. The pellets were finally collected in sterile distilled water and cell populations were adjusted to 108 cfu ml−1 as measured spectrophotometrically (Thompson, 1996).