Question

If you add 43 of food in 350 ml water and dilution of 1:6 is made then from this dilution 1:90 is made and from this 1 ml is added to 60 ml of water then 0.1 ml from this last dilution is plated and after incubation 143 colonies are counted what is the total count per g of original sample

Answer 1

Solution:

DF = Initial dilution * Subsequent dilution * Amount Plated

Total Count Per g = $\frac{1}{DF}$ * Colonies Counted

Initial dilution : $\frac{43}{(43+350)}=\frac{43}{393}$

Subsequent dilution : $(\frac{1}{6} )*(\frac{1}{90} )*(\frac{1}{61} )$

Amount Plated : 0.1

Colonies Counted : 143

DF = $\frac{43}{393}*\frac{1}{6}*\frac{1}{90}*\frac{1}{61}*0.1$

DF=$\frac{43}{393}*\frac{1}{6}*\frac{1}{90}*\frac{1}{61}*\frac{1}{10}$

DF = $\frac{43}{129454200}$

Total Count Per g = $(\frac{129454200}{43} )*143$

Total Count Per g = $4.3*10^{8}$