One gram of soil was suspended in 99 ml saline and thoroughl

One gram of soil was suspended in 99 ml saline and thoroughly mixed. From this suspension, 5serial, 1/10 dilutions weremade. 100hundred microliters of each of the last four serial dilutionswereused for spread plating on TYmedia, resulting in 1245colonies, 598colonies, 69colonies and 12colonies. What do you calculate as the bacterial concentration in the soil? (Foryour information 1 gram = 1 ml)

Solution

First thing we have to calculate Dilution Factor:

here Initially 1g soil is suspended in 99ml = Final Volume / Sample volume = 100/1 = 100

Then five serial dilutions of 1/10

Total Dilution Factor = 100 * 10 *10 *10 *10 *10 = 10^7

Volume used for culture in ml= 100 *10^-6 ml= 10^-4ml

CFU/ gram= (No. of colony* Dilution factor) / volume of culture plate

CFU/g on the basis of 12 colonies, CFU/g = (12* 10^7)/ 10^-4

CFU/g = (12* 10^7) * 10^4 = 12 * 10^11

Total colony forming unit of soil or bacterial concentration in soil is = 1.2 *10^12 CFU/g