Undiluted
and 101 dilutions of the lysates were plated in duplicates onto MacConkey
agar plates and incubated for 14 to 16 hours at 37°C. Isolates
were considered cytotoxic if they exhibited Trypan blue staining with
low invasion numbers, invasive if they if exhibited low or no Trypan
blue staining and high invasion numbers, and neither phenotype if they
exhibited low or no Trypan blue staining and low invasion numbers.