Science Buddies: "Ask an Expert"

Hello!

I am looking to do the "Do Different Dilutions of Disinfectants Affect the Development of Bacterial Resistance?" experiment for a school project. I am a little confused as to what the procedure means by "pick[ing] up bacterial colonies growing closest to the disinfectant-impregnated disk." Does that mean to pick up bacteria just outside of the inhibition zone created by the disinfectant solution or to pick up bacteria within the inhibition zone next to the disc?

I hope someone knows!

Thank you!

Hello there,

Wikipedia's article on the diffusion disk test does a pretty good job explaining the method and how it works, so you should take a look at it. http://en.wikipedia.org/wiki/Agar_diffusion_test

Basically, the zones of inhibition are created because the compound in the disk has diffused out and if they're antibacterial, they should inhibit growth of bacteria around the disk, and the zones of clearing around the disk are where the bacteria can't grow. Hence, there technically wouldn't be any bacteria inside the zones of clearance. So when the procedure says "pick bacterial colonies growing closest to the disk", it means the bacteria just right outside the inhibition zone.

Hope that helped!

Connie

Thank you Connie!

That's what I was thinking but for some reason how the procedure was written baffled me.

Thanks so much; now off to start the project!

Awesome! I hope your experiments go well. Let us know if you have any more questions along the way!

Connie