1 pts You buy raw milk and when you come home and taste it it\'s a bit sour. You
ID: 212085 • Letter: 1
Question
1 pts You buy raw milk and when you come home and taste it it's a bit sour. You want to know how many bacteria are in your bottle per 1 ml milk. You decide to perform a dilution series to determine the number and report it to the store to get your money back You take 1ml from your original milk bottle, and add it to 9ml of buffer. Then you take.5ml from that dilution, and add it to 4.5mi of buffer. Then you take 3ml of that, and add it to 27ml of buffer. Then you take 1ml of that, and add it to 99ml of buffer. Finally, you plate 10ul of the last dilution. You counts come back the next day as 107 How many CFU's/ml were in your original stock? 1.07 x 10 tyour answer here) cFU/miExplanation / Answer
Dilution I = 1 mL milk + 9 mL buffer = 1/10
Dilution II = 0.5 mL of dilution I + 4.5 mL of buffer = 1/10 X 1/10 = 1/100
Dilution III = 3 mL of dilution II + 27 mL of buffer = 1/100 X 1/10 = 1/1000
Dilution IV = 1 mL of dilution III + 99 mL of buffer = 1/1000 X 1/100 = 1/100000 = 10^-5
From this, 10 uL is plated.
Number of colonies observed = 107/10 uL = 10.7/uL
= 1.07 X 10^7/mL
Original concentration = 1.07 X 10^7 X 10^5 CFU/mL
= 1.07 X 10^12 CFU/mL
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