You are given a sample of unknown Bacilus subtilus and need to find out the cell

Question

You are given a sample of unknown Bacilus subtilus and need to find out the cell concentration of the original sample. Describe your experimental design. Draw out a dilution map that illustrates your experimental design. Be sure to label the amount of autoclaved water going in to each vial, volume of bacteria sample transferred, the plating volume and determine the resulting concentration that it will produce after being plated.

What is the original cell density of a sample that produced 117 colonies on a plate that was inoculated with a 0.1mL sample from a tube containing a 10-5 dilution?

What is the original cell density of a sample that produced 32 colonies on a 10-7dilution plate?

If you only have three agar plates left that are suitable to grow V. fischeri and your original cell sample was 2.6x105, which three dilution vials would you inoculate in order to guarantee yourself a countable plate? Assume the inoculation volume used on each plate was 0.1mL and that each vial had a dilution factor of 10.

Explanation / Answer

1)

Based on the given data, assume that you have given 0.5 mL of unknown bacterial sample. For example, take 0.1 Milliliter of unknown Bacilus subtilus, and then it is added to 9.9 ml of autoclaved water. So, the final dilution factor of tube is

Now from this 10 mL tube, take 1 mL sample and spread on to a nutrient plate. You have observed that 270 colonies on the plate after 24 hours incubation. So, (0.1 ml of unknown sample) dilute sample has original cell density (OCD) about:

So, 1 mL CFU/mL, and 10 mL contains CFU/mL (for 0.1 mL of unknown sample). Therefore, the final cell volume of 0.5 ml unknown sample is: CFU/mL. Likewise, you can take different mL from unknown sample and add different volumes of autoclaved water. Then you can check for DF and total CFU of unknown sample.

2)

Here, the DF is 1×10-5 and number of colonies observed are 117. So, OCD is

Thus, the original cell density is CFU/ 0.1 mL.

3)

Here, the DF is 1×10-7 and number of colonies observed are 32. So, OCD is

Thus, the original cell density is CFU/ 0.1 mL.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.