Question

Serial Dilution Question:

A 50mL sample of ground beef in water arrives from a meat packing plant to your microbiology lab. The plant manager has submitted the sample for analysis to determine approximately how many bacterial cells are present per mL of the ground beef slurry.

Using the sample as your stock solution, describe how to prepare a serial dilution from 1:10 to 1:106. Use water as the solvent. Create a bulleted list describing what volumes are being transferred, and how much solvent is added each time. Indicate how much liquid will be left in each tube (the original sample and all of the dilution tubes) at the end of the process. Use the example from the middle of page 3 as your model.

Answer 1

Here is a bulleted list of steps to prepare a serial dilution from 1:10 to 1:10^6 using a 50mL sample of ground beef in water:

- Label five sterile tubes as follows: Tube 1 (stock tube), Tube 2 (10^-1 dilution), Tube 3 (10^-2 dilution), Tube 4 (10^-3 dilution), and Tube 5 (10^-4 dilution).

- To Tube 1, add the entire 50mL sample of ground beef in water.

- To Tube 2, add 4.5mL of sterile water and 0.5mL from Tube 1. This is a 1:10 dilution.

- Mix Tube 2 thoroughly and transfer 0.5mL to Tube 3.

- To Tube 3, add 4.5mL of sterile water. This is a 1:100 dilution.

- Mix Tube 3 thoroughly and transfer 0.5mL to Tube 4.

- To Tube 4, add 4.5mL of sterile water. This is a 1:1000 dilution.

- Mix Tube 4 thoroughly and transfer 0.5mL to Tube 5.

- To Tube 5, add 4.5mL of sterile water. This is a 1:10,000 dilution.

- Mix Tube 5 thoroughly.

- Discard the remaining content of Tube 5, as it has a large enough dilution factor to exceed the 1:10^6 dilution.

- Tubes 1-4 each have 0.5mL of liquid in them, while Tube 5 has been discarded completely.

Step-by-step explanation: