You have 005 mL of an undiluted culture at a density of 36 t

You have 0.05 mL of an undiluted culture at a density of 3.6 times 10^6 CFU/mL. You then add 4.95 mL sterile diluent. What is the dilution and what is the final density of cells? You hate 0.3 mL of an undiluted culture at a density of 4.2 times 10^7 CFU/mL. You then add 2.7 mL sterile diluent. What is the dilution and what is the final density of cells?

Solution

5. Initial volume of culture = 0.05ml

Volume of Sterile diluents added to the culture = 4.95ml

Therefore, total volume of culture = 4.95 ml + 0.05ml

                                                    = 5ml

Hence, dilution factor     =   Total volume of final culture ÷ Initial Volume

= 5 ÷ 0.05 = 100

Initial cell density = 3.6 X 10⁶ CFU/mL

Final cell density = Initial density ÷ Dilution

                              = 3.6 X 10⁶ ÷ 100

                              = 3.6 X 10⁴ CFU/mL

Therefore, the culture is diluted 100 times after addition of sterile diluent and the final density of cells also reduced 100 fold i.e. to 3.6 X 10⁴ CFU/mL.

6. Initial volume of culture = 0.3ml

Volume of Sterile diluent added to the culture = 2.7ml

Therefore, total volume of culture = 2.7 ml + 0.3ml = 3 ml

Hence, dilution factor     =   Total volume of final culture ÷ Initial Volume

= 3 ÷ 0.3 = 10

Initial cell density = 4.2 X 10⁷ CFU/mL

Final cell density = Initial density ÷ Dilution

                              = 4.2 X 10⁷ ÷ 10

                              = 4.2 X 10⁶ CFU/mL

Therefore, the culture is diluted 10 times after addition of sterile diluent and the final density of cells also reduced 10 fold i.e. to 4.2 X 10⁶ CFU/mL.