A nutrient agar plate labeled 10^-5mL produced 154 colonies after incubation. a.What was the cell density in the original sample? b. What combination(s) of volumes and dilution factors could have been used to inoculate this plate? (note two possibilities) Solution a) Original cell density = CFU / (dilution x Volume) = 154 / 10 -5 x 0.1 mL = 154 x 106 = 1.54 x 108 CFU/ml.