![]() If you then have 30 colonies, you thus have: 30 colonies/1ml from a 10^-2 diluted sample. If you than plate out 1ml of this sample (from the second tube/dilution) in a plate you have: 1 plate with 1ml of a 10^-2 dilution. If you have 30 colonies on a plate and you have a 10^-2 dilution than you have 30 colonies for that dilution (+ you have to take into the account the amount you placed on your plates)ġ ml to 9 ml (10^-1 solution), then from this sample 1 ml to another 9ml, thus you have a 10^-2 dilution in your second dilution/tube. Use common sense and think about it, its all very logical! ![]() This is how people make so many mistakes! May I know is the calculation method get wrong? How come the answer is 30 x 10^-2 (0.3) instead of 30x10^2? If I obtained 30 colonies from second dilution tube (10^-2), Btw, if we following the formula,ĬFU= (#colony x dilution factor)/volume plated in mL Thank you.Where you have it wrong is that in your dilution series you are taking 1/10th EACH time you dilute, so from your initial 1 g, at the next step you are taking 0.1 g to the new tube, and the next 0.01 g and the next 0.001 g and so on. What if I added 1g of sample directly to 99mL of broth, what is the dilution factor here? According to formula it will be 1/100mL or 10^-2? But 100mL is equivalent to 11 tubes of 9mL broth, so if look at this way, it will be 10^-11 instead of 10^-2? ![]() ![]() ![]() Thus, if 1000mL of sample in tube 11 plated onto the agar and I obtained 30 colonies in this plate, CFU = (30 x 10^-11)/1000mLCorrect this far. As far as I know, dilution factor = volume of sample/total volume and CFU = (#colony x dilution factor)/volume plated in mL.įor example, if I added 1g of sample into 9mL of broth - 10^-1, and transfer 1mL from 10^-1 to second tube (9mL as well). I am confused regarding the calculation of dilution factor. ![]()
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