Isolates are obtained in pure culture from enriched cultures by streaking on suitable medium, such as glucose-peptone-yeast extract agar and YM agar. Persistent bacterial contermination can be eliminated by acidifying the media or by adding antibiotics. These primary plates are inspected, preferably under low magnification, for the presence of colonies of more than one form. Single, well separated colonies of each form are selected and streaked again (Yarrow, 1998).