Question

10 multiple choice 0.8 points if you obtain 100 colonies after plating 0.3 ml sample from the basin after the scrubbing experiment, what is the total number of bacteria in the 1 liter sample in the basin? (you may use only the calculator from the lockdown browser) 2.25 x 10^6 cfu/l 3.3 x 10^5 cfu/l 3.3 x 10^4 cfu/l 2.25 x 10^4 cfu/l 3.0 x 10^6 cfu/l

Explanation:

Step1: Calculate bacteria per ml

We know that 100 colonies are from a 0.3 ml sample. So the number of bacteria per ml ($N_{per - ml}$) is calculated by the ratio. $N_{per - ml}=\frac{100}{0.3}=\frac{1000}{3}$ cfu/ml.

Step2: Convert 1 liter to ml

Since 1 liter = 1000 ml.

Step3: Calculate bacteria in 1 liter

The total number of bacteria in 1 liter ($N_{total}$) is the number of bacteria per ml times the number of ml in 1 liter. $N_{total}=N_{per - ml}\times1000=\frac{1000}{3}\times1000=\frac{1000000}{3}\approx3.3\times 10^{5}$ cfu/L.

Answer:

3.3 x 10⁵ cfu/L (corresponding to the second option)