Question

Sketch a dilution scheme using 99 ml or 9 ml dilution blanks (or both) that would produce a countable plate (between 30 and 300 colonies) for an original stock culture with 4,700,000CFU/mJ.

Answer 1

If we sonsider original stock as solution A (concentration 4700000 CFU/ml )

(Step 1)- 1:100 dilution

99 ml of nutrient broth +1 ml of solution A ------------------ Solution B (concentration 47000 CFU/ml )

(Step 2)- 1:100 dilution

99 ml of nutrient broth +1 ml of solution B--------------------Solution C (concentration 470 CFU/ml )

Step 3 (1:10 dilution)

9 ml of nutrient broth +1 ml of solution C--------------------Solution D (concentration 47 CFU/ml )

Step 4

Plate 1 ml of solution D on a nutrient rich medium to get approximately 47 CFU/plate after incubation .