A 10-5 is performed on a culture of bacteria in order to perform viable plate co
ID: 575150 • Letter: A
Question
A 10-5 is performed on a culture of bacteria in order to perform viable plate counts. From the dilution, *0.1 mL* of solution is plated on solid media, and 35 colonies of bacteria grow on the plate. Assuming each colony came from a single bacterium, how many bacteria are in a single mL of the original culture? Express your answer to two decimal places using exponential notation. Since only 0.1 mL is put on the plate, this counts as an extra dilution!!! Any time less than 1 mL is transfered, a dilution is being performed. Any time more than 1 mL is transfered, a concentration is being performed
Explanation / Answer
Ans. Dilution = 10-5
Volume of inoculum taken form 10-5 dilution = 0.10 mL
No. of CFU arising from 0.10 inoculum = 35 CFU
#. Now, No. of CFU per mL inoculum = No. of CFU obtained / Volume of inoculum
= 35 CFU / 0.10 mL
= 350 CFU/ mL
Since 1 CFU is equivalent to 1 bacteria, the concertation of inoculum = 350 cell/ mL
Therefore, cell count in 10-5 dilution = 350 cells / mL
# Cell count in original culture = Cell count of 10-5 dilution / Dilution factor
= (350 cells/ mL) / 10-5
= 3.50 x 10-7 cells/ mL
Therefore, total number of cells in 1.0 mL of original culture = 3.5 x 107 cells
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