Twenty grams of soil was added to 50 mL of water. After mixing, the suspension was...

Twenty grams of soil was added to 50 mL of water. After mixing, the suspension was serially diluted and used to inoculate spread plates (0.125 mL per plate). The inocula from the three highest dilutions, 10-4, 10-5, and 10-6, produced 210, 29, and 2 colonies, respectively. What was the bacterial concentration in the soil? (3 pt)

Expert Solution

number of colonies in the range of 30 to 300 is used to calculate the CFU/mL

so let`s use dilution 10^-5 for the calculation of CFU/mL

CFU/mL= number of colonies/( dilution volume plated in mL)

volume plated =0.125 mL

dilution=10^-5

number of colonies=210

CFU/mL= 210/(10^-50.125)

= 1.6810^8/mL

bacterial concentration in the 50 mL is 1.6810^8/ mL

so total number of bacteria in the 50 mL= 501.6810^8=8.410^9 cells

50 mL of the solution contains 20 gram of soil, the number of bacteria in the20 grams of the soil is 8.410^9 cells so total number of cells per gram of the soil= number of bacteria in 20 grams of soil/20=8.410^9/20=4.210^8 /gram.

gladiator answered 3 years ago

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