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You have an original cell density of 2.10 x 107 CFU/mL. What is this number in its non-scientific notation or “regular” format?

If you’ve taken 500 ul of a bacterial culture and added 500 ul of DI water, you have achieved what dilution (i.e. what is the dilution factor)?

Group of answer choices

1:4 (or 1/4)

1:2 (or 1/2)

1:3 (or 1/3)

You conduct the following serial dilution:

Step 1: You’ve diluted 100 ul of a bacterial stock with 800 ul distilled water, but the sample still needs further dilution

Step 2: You then take 100 ul of the dilution from step 1 and dilute it further with 400 ul of distilled water.

A.) What is the dilution factor after Step 1? (2 points)

B.) What is the final/total dilution factor at the end of Step 2 from the starting stock? (2 points)

Show your work for both.

You conduct the following serial dilution:

Step 1: In tube 1, you add 10 ul of plasma to 990 ul of distilled water.

Step 2: In tube 2, you then take 100 ul from tube 1 and add 900 ul of distilled water.

Step 3: In tube 3, you then take 100 ul from tube 2 and add 900 ul of distilled water.

What is the final/total dilution factor in tube 3 at the end of step 3

You were instructed to add 2.0 mL out of 6.0 mL of an undiluted sample to 98 mL of sterile diluent. Instead, you add the entire 6.0 mL to the 98 mL.

A.) What was your intended dilution factor? (2 points)

B.) What was your actual dilution factor? (2 points)

Show your work.

The plate with 242 colonies was inoculated with 100 µL Volume of a 10-9 Dilution.

Given the formula OCD = CFU/V x D, what as the Original Colony Density?

You spread 0.1 mL volume of a 10-7 dilution onto a nutrient agar plate. After 24 hours of incubation at 37°C, there were 140 colonies of bacteria on the plate.

A.) What is the original concentration (OCD) of bacteria in the stock sample this dilution came from? (2 points)

B.) Using the OCD value from part A, determine the number of colonies that would be expected to grow on a plate that is inoculated with 0.1 mL volume of 10-9 dilution from this same stock of bacteria. (2 points)

Shbciow your work for both.

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