Oh no, it's serial dilution
A stock culture of M. luteus underwent serial dilution. Then, 0.1 ml of suspension was removed from each tube and spread on a plate, and the colonies were counted, producing the following result -
Tube 1: 1ml cells into 99ml water (TNTC)
Tube 2: 1ml cells into 99ml water (250 colonies)
Tube 3: 1ml cells into 9ml water (65 colonies)
Tube 4: 1ml cells into 9 ml water (18 colonies)
What is the CFU/ml of the stock culture
Tube 1: 10-2
Tube 2: 10-2
Tube 3: 10-1 , total dilution = 10-2+10-2+10-1 = 10-5
Dilution factor = 105
CFU/ml = colonies x DF x plating factor
65 colonies x 105 x 10 =
65 x 106 =
6.5x 107 CFU/ml