5 g tryptone; 5 g soytone; 5 g beef extract; 2.5 g yeast extract;
0.5 g ascorbic acid; 0.25 g magnesium sulfate; 19 g sodium glycerophosphate;
and 11 g agar were dissolved in 950 mL distilled
water. The medium was autoclaved at 121 C for 15 min. For the
lactose solution, 10 g lactose were dissolved in 100 mL distilled
water, and the solution was sterilized by filtration through 0.22 mm
membrane filter (Millipore, Sao Paulo, Brazil). Immediately before
use, 5 mL lactose solution was added to each 95 mL M17 agar