ST agar 10 g tryptone, 10 g sucrose, 5 g yeast extract, 2 g K2HPO4 were dissolved in 1 L distilled water. The pH was adjusted to 6.8 ± 0.1 and 6 mL bromocresol purple and 12 g agar were added to the medium. The medium was autoclaved at 121 C for 15 min