7. If the surface area of the plates is overgrown and it is not possible to select well isolated characteristic colonies, an attempt shall be made to subculture 3 suspect colonies onto duplicate EY-free TSC agar plates and incubated anaerobically at 37°C ± 1°C for 20 hours ± 2 hours. Subsequent purification may be required in order to obtain well isolated colonies of suspect organism.