The cells were then rinsed twice with phosphate-buffered saline (PBS) prewarmed to 37°C and, after the addition of a 0.1-ml volume of 1× trypsin-EDTA (Invitrogen), incubated for 10 min at 37°C. Next, a 0.9-ml volume of PBS was added to each well, the cell suspension was mixed, and a set of serial dilutions was prepared and plated out on solid MRS medium