Question

You are given a culture that has a concentration of 2.1x10^9 cfu.ml. you are asked to dilute it and plate it so that you have 270 colonies on one plate. you are given plenty diluent but only 4 tubes with which to make your dilutions. Demonstrate how you would set up the dilution. For each step indicate in an orderly fashion the V2, V1, Diluent volume, dilution, c-dilution, DF, CDF up to that step and the concentration of each tube.

Answer 1

let first we dilute to get a concentration of 2.7X10⁸ in 10 ml

So N1V1=N2V2

      2.1x10^9XV1=2.7X10⁸X10

SoV1=1.2857X10^-1

that measn 0.12857 ml to be dilutd 10 ml we get 2.7X10^{8 cfu.ml}

	T1 (2.1x10^9)	T2 (2.7X108)	T3 (2.7X106)	T4 (2.7X104)
Stock ml	0.12857	0.1 ul	0.1 ul	0.1 ul
DIluent up to ml	10	9.9 ml	9.9 ml	9.9
CFu.ml	2.7X108	2.7X106	2.7X104	270