You have prepared the spread plates below using 01 mL from a

You have prepared the spread plates below using 0.1 mL from a liquid culture of E. coli at an unknown concentration. Count the colonies that have grown and use the information, together with the TDF for the corresponding plate, to calculate the average original concentration of your E. coli suspension.

Solution

to calculate the average original concentration of e.coli suspension,

first we need to find out CFU/ML by formula-

no. of colonies x dilution factor / volume of culture plate

for plate first- TDF-2 x 10⁵, so total number of colony is 12 x ( 2x10⁵) / 0.1 ml = 24x10⁶

second plate TDF is 1 x 10⁶, so CFU/ml is = 6 x 10⁷

so overall average CFU/ml is = 1.5 x 10¹⁴ by taking average of both plate sample add both value than divide by 2 so the final outcome is  1.5 x 10^14, the final concentration of E.coli suspension is 1.5 x 10¹⁴ u/ml.