A 10 -1 is performed on a culture of bacteria in order to perform viable plate c
ID: 151268 • Letter: A
Question
A 10-1 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 80 colony forming units grow on the plate.
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
Number of bacteria in a single ml of the original culture is determined in CFU/ml. [CFU-Colony forming units]
CFU/ml= (No of colonies X Dilution factor)/ Volume of culture plated
So in the above question:
No of colonies= 80
Dilution= 10-1
Dilution factor= 101 [ we are changing the sign from negative to positive i.e 101. This is because we need only the factor or times by which the main culture was diluted]
Volume of culture plated= 0.1 ml
Therefore,
CFU/ml= 80X101/0.1= 8000 CFU/ml =0.08X105 CFU/ml
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