You put 1 ml of culture into 9 ml of broth diluent, and then you put 1 ml of that dilution into 9 ml of broth diluent, and then again you put 1 ml of the diluted culture into 9 ml of broth diluent. You inoculated an agar plate with 1 ml of the most diluted tube and 45 colonies grew overnight. What is the original bacterial density (CFU/ml) in the original undiluted culture?

Question

You put 1 ml of culture into 9 ml of broth diluent, and then you put 1 ml of that dilution into 9 ml of broth diluent, and then again you put 1 ml of the diluted culture into 9 ml of broth diluent. You inoculated an agar plate with 1 ml of the most diluted tube and 45 colonies grew overnight. What is the original bacterial density (CFU/ml) in the original undiluted culture?

4,500 CFU/ml
45,000 CFU/ml
450 CFU/ml
9,000 CFU/ml

Answer 1

The original bacterial density (CFU/ml) in the original undiluted culture is 45,000 CFU/ml.

Answer 2

To calculate the original bacterial density (CFU/ml) in the original undiluted culture, we need to follow the dilution series and use the colony count from the agar plate.

First, let's break down the dilution series:

1. We start with the original culture volume of 1 ml.
2. This 1 ml is added to 9 ml of broth diluent to create a 1:10 dilution.
3. From this 1:10 dilution, we take 1 ml and add it to 9 ml of broth diluent to create a 1:100 dilution.
4. Finally, from the 1:100 dilution, we take 1 ml and add it to 9 ml of broth diluent to create a 1:1,000 dilution.

Now, we take 1 ml from the most diluted tube (1:1,000 dilution) and inoculate an agar plate. After incubation, we count 45 colonies.

To calculate the original bacterial density, we need to consider the dilution factor. The dilution factor is the reciprocal of the dilution ratio. In this case, the dilution factor for the plate is 1:1,000.

So, we can calculate the original bacterial density using the following formula:

Original bacterial density = (Colonies counted / Volume plated) * Dilution factor

Plugging in the values:

Original bacterial density = (45 colonies / 1 ml) * 1,000

The original bacterial density is therefore 45,000 CFU/ml. So, the correct answer is 45,000 CFU/ml.

Answer 3

To calculate the original bacterial density (CFU/ml) in the original undiluted culture, we can use the dilution factor and the number of colonies grown on the agar plate.

The dilution factor is calculated by multiplying the dilution for each step. In this case, the dilution factor is:

1/10 * 1/10 * 1/10 = 1/1000

Now, we can calculate the original bacterial density by dividing the number of colonies grown on the agar plate by the dilution factor:

45 colonies / (1/1000) = 45,000 CFU/ml

Thus, the correct answer is 45,000 CFU/ml.