Question

Name One use of serial dilutions is to calculate the concentration of microorganisms. Since it would usually be challenging or even impossible to actually count the number of microorganisms in a sample, the sample is diluted and plated to get a reasonable number of colonies to count (usually between 25 to 250 colonies is the goal). Since each colony on an agar plate theoretically grew from a single microorganism, the number of colonies or Colony Forming Units is representative of the number of viable microorganisms. Since the dilution factor is known, the number of microorganisms per ml in the original culture (cru/m.oc) can be calculated. Serial Dilution equations from your lab manual: Equation 1: IDF Volume transferred Volume transferred + volume of diluent in the blank Equation 2: TDFn = (IDF)a (IDF)b (IDF)c (IDF)n where a, b, c, n refer to different dilutions in the series. Equation 3: CFU/mLoc = number of colonies/mL plated TDF of the culture used for plating Equation 4: CFU/mLtube = (CFU/mL original culture) (TDFtube) Equation 5: CFUplate = (CFU/mLtube)(mL plated) Laws of Exponents a . amen Add exponents 2.2 = (221222) - 28 product 2.222 - 201 - 2 quotient Subtract exponents (a = am Multiply exponents Rey=122:212-2212-22) -2° power 2' (this is a definition) inverse Take the reciprocal Anything raised to the zero ao = 1 201 power is one zero exponent

please help with whatever possible. thank you so much in advance.

Answer 1

a)

Tube	A	B	C	D	E
IDF	$10^{-1}$	$10^{-2}$	$10^{-3}$	$10^{-3}$	$10^{-1}$
TDF	$10^{-1}$	$10^{-3}$	$10^{-6}$	$10^{-9}$	$10^{-10}$

Plate Dilution Factor (P.D.F.) will be calculated as:- the amount of culture dropped on plate/1 mL

therefore, PDF= 0.1/1= 0.1= 1/10

Final Dilution Factor (FDF) = TDF X PDF=

10-10 x 10-1 = 10-11

b) CFU/mL of original culture = no of colonies on plate X 1/FDF= 90 X $10^{11}$ CFU/mL

c) CFU/mL of Tube B= CFU/mL of original culture X TDF (of tube B)= 90 X $10^{11}$ X $10^{-3}$ = 90 X $10^{8}$ CFU/mL

CFU/mL of Tube E= CFU/mL of original culture X TDF (of tube E)= 90 X $10^{11}$ X $10^{-10}$ = 90 X 10= 900 CFU/mL

d) As CFU/mL of tube B is 90 X $10^{8}$ so on plating 0.1 ml, number of colonies will be 90 X $10^{7}$ .