Diluting cell suspensions before plating Sample to 1 ml be counted 1 ml 1 ml 1 ml 1 ml 1 ml 9-ml broth Total 1/10 1/100 1/103 1/104 1/105 1/105 dilution (10-1) (10-2) (10-3) (10-4) (105) (106) Plate 1-ml samples 159 17 2 0 Too many coloniescolonies colonies colonies colonies to count 159×103 =1.59×105 Plate Dilution Cells(colony-forming units) 30-300 colonies/plate will be counted count factor per milliliter of original sampleDiluting cell suspensions before plating 30-300 colonies/plate will be counted