Question

m e usually performed, e.g., 10°>10% 10% 10%, etc. Two-fold or other dilution schemes can be applied as well. For accurate quantitation, it is important to use the selected dilution scheme consistently. correction factor is 10 (0.1 ml X 10-10 ml). If you plated 0.5 ml, the correction factor is 2. 1.-CFU/Dr Initial concentration, (lc) equals colony forming units (cfu) divided by dilution factor (Df). Note that each step of the dilution procedure reduces the number of microbes by a factor of ten. A"countable pumber of colonies on an agar plate lies between 30 and 300. How can you produce a countable number from so many bacteria? For example, if you plated 0.1 ml from the 1:100,000 dilution and obtained 150 colonies, the cfu/ml for that culture would be: #colonies on the plate X volume correction factor X dilution factor Samples from the dilutions are then aliquoted" (that is, specified volumes are transferred) to the surfaces of agar plates, spread evenly over the surface of the plate, and incubated at a temperature that allows bacterial growth and the formation of colonies, Tunically, this volume is 0.1 ml, which 150 X 10 X 100,000, or car 150,000,000 cfu/ml. 30-300 observation og kossa 1074 TMTC 106 (ago 0 IC - CFU - 280 DF 105

help me with the math.

Answer 1

From the observation, colonies at dilution 10^-4 are Too Numerous to Count. Colonies at dilution 10^-6 are 26, which is below 30 and hence too few to count.

For dilution 10^-5, colonies are 280 which falls between 30 and 300. So this value will be taken for calculation of initial culture concentration.

IC = CFU/DF (CFU= colony forming unit, DF = dilution factor)

Here CFU = 280

DF = 10^-5

IC = 280/10^-5 = 280 x 10⁵ = 2.8 x 10⁷

[10^-5 means 1/10⁵. 280/10^-5 = 280/(1/10⁵) = 280 x 10⁵]