Question

question 4
a sample of raw, unpasteurized milk is tested for its bacterial content in a plate
count assay. a 0.1ml sample of the milk is diluted in a 0.1 dilution series just like
what we did in class. after the dilutions are made 0.1mls of the 10^-6 dilution tube
was plated on nutrient agar. after incubation, this plate had 282 colonies. how
many cfus were in the original milk sample?
2.82 x 109 cells per ml
2.82 x 1010 cells per ml
28.2 x 1010 cells per ml
28.2 x 109 cells per ml
the answer cannot be determined with the provided data
question 5
what does cfu stand for?

Explanation:

Step1: Recall the formula for calculating CFU

The formula for calculating the number of CFUs (Colony - Forming Units) in the original sample is \(CFU/mL=\frac{\text{Number of colonies}\times\text{Dilution factor}}{\text{Volume of plated sample (mL)}}\)

Step2: Identify the values

• The number of colonies \(= 282\)
• The dilution factor: The dilution is \(10^{-6}\), so the dilution factor \(=\frac{1}{10^{-6}} = 10^{6}\)
• The volume of the plated sample \(V = 0.1mL\)

Step3: Calculate the CFU/mL

Substitute the values into the formula:

$$
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$$

Answer:

\(2.82\times10^{9}\) cells per mL (the first option)