You diluted a bacterial culture 106, plated out 200 µL and found 38 colonies on the plate. How many bacteria/mL were in the original undiluted culture?

To calculate the number of bacteria/mL in the original undiluted culture, you can use the following steps:

Step 1: Calculate the dilution factor
The dilution factor is the ratio of the volume plated (200 µL) to the total volume plated (in this case, the total volume plated is equal to the volume of the original culture before dilution).

Dilution Factor = (Volume Plated)/(Total Volume Plated)
Dilution Factor = (200 µL)/(Total Volume Plated)

Step 2: Calculate the total volume plated
The total volume plated is the volume of the original culture before dilution. Since you used 200 µL for plating, the total volume plated is equal to 200 µL.

Total Volume Plated = 200 µL

Step 3: Calculate the total number of bacteria in the original culture
The total number of bacteria in the original culture can be calculated by multiplying the dilution factor by the number of colonies counted on the plate.

Total Number of Bacteria = Dilution Factor x Number of Colonies
Total Number of Bacteria = Dilution Factor x 38

Step 4: Calculate the number of bacteria/mL in the original undiluted culture
To calculate the number of bacteria/mL in the original undiluted culture, we need to divide the total number of bacteria by the total volume plated.

Number of Bacteria/mL (Original Undiluted Culture) = Total Number of Bacteria/Total Volume Plated
Number of Bacteria/mL (Original Undiluted Culture) = Total Number of Bacteria/200 µL

By using these steps and the given information, you can calculate the number of bacteria/mL in the original undiluted culture.

To calculate the number of bacteria/mL in the original undiluted culture, we need to take into account the dilution factor and the number of colonies found on the plate. Here's how you can determine the answer:

1. Calculate the dilution factor:
The dilution factor is the ratio of the volume plated (200 µL) to the total volume of the diluted culture. In this case, the total volume of the diluted culture is not mentioned, so we'll need to assume it. Let's assume the total diluted culture volume was 10 mL. Therefore, the dilution factor is:
Dilution factor = Total diluted culture volume / Volume plated
= 10 mL / 200 µL
= 50

2. Calculate the total number of bacteria in the diluted culture:
The number of bacteria in the diluted culture can be determined by multiplying the number of colonies counted on the plate by the dilution factor. In this case, the number of colonies is 38 and the dilution factor is 50. Therefore,
Total number of bacteria in the diluted culture = Number of colonies × Dilution factor
= 38 × 50
= 1900

3. Calculate the number of bacteria/mL in the original undiluted culture:
Since we assumed that the total diluted culture volume was 10 mL, we can now calculate the number of bacteria per mL in the original undiluted culture by dividing the total number of bacteria in the diluted culture by the total diluted culture volume. Therefore,
Number of bacteria/mL in the original undiluted culture = Total number of bacteria in diluted culture / Total diluted culture volume
= 1900 / 10
= 190 bacteria/mL

So, the number of bacteria/mL in the original undiluted culture is 190.