Science Buddies: "Ask an Expert"

Hello everyone,

I am currently a Junior in high school, and I was interested in doing the Biowarfare: Experiment with Viruses that Destroy Bacteria . It seems to be quite an interesting topic, and I'm really excited to get started! I just had a question regarding the procedure:

1) Regarding the procedure, I understand the first and the last part about raising the E. Coli culture and collecting data, but I'm not sure how the phage dilution process works. I'm really interested in this topic, but because my passion is new, my knowledge is still limited! Can anyone explain to me how that process works?

A link to the project is below for your convenience. Any help would be appreciated! Thanks!

https://www.sciencebuddies.org/science- ... p029.shtml

Hi Shawn and welcome to Scibuddies!

The bacteriophage experiment is one of the most interesting ones, but you are right that making the dilutions correctly can be a little confusing. The procedure is called making serial dilutions because you are pipetting the same amount from one tube to the next--serially--and each tube is one tenth as concentrated as the one before it. You are making ten-fold dilutions each time by adding 1 mL to 9 mL or 1:10. The broth tubes contain 9 mL of broth, so when you add 1 mL of the phage culture to the first tube [labelled 10 to the minus one, or 0.10] you have a suspension of phage that is now one-tenth as concentrated as in the original tube.

Now you swirl the 0.10 tube until the phage are all mixed completely then pipet 1.0 mL from this tube into the next tube that is labelled 10 to the minus 2 or 0.01--a one to one hundred dilution. Do you see how this works now? Just keep doing serial dilutions until you get to the 10 to the minus 5 tube. This is where it gets a little more complicated because from now on you have to add 0.1 mL of the phage suspension to a soft agar tube and 1.0 mL to the next broth dilution tube. So, instead of pipetting 1.0 mL, you have to pipet 1.1 mL. Make sure ahead of time that your pipet has a 1.1 mL mark, or if you are using an adjustable pipetter that you can set it to 1.1 mL.

If you want to watch how a serial dilution is done you can look on youtube for 'how to make serial dilutions'. Here's an example:

https://www.youtube.com/watch?v=BH4teQkPBhY

If you have more questions, be sure to let us know. It is better to be certain about a step by asking us than to make a mistake and ruin the experiment.

Good luck!

Sybee