Science Buddies: "Ask an Expert"

My question is:

Do bacterial colonies growing closest a zone of inbition on an agar plate have an increased resistance to the bacteria compared to the bacterial colonies farther away?

If I build an experiment using rounds of selection would it make sense to choose colonies closest to the zone of inhibtion?

I think your approach of picking colonies closest to the zone of inhibition would be valid. I would assume that the bacteria closest to the zone would be exposed to higher levels of the antibacterial agent than those colonies further away from the zone. Consequently, these colonies will be under stronger selection pressure than those farther away.

I believe you should think of the zone of inhibition in term of concentration of the disinfectant. The zone of inhibition is the critical point where the amount of drug at that distance is unable to inhibit the growth of the organism that you are using. Therefore bacteria grow closet to the zone of inhibition do not necessary mean they have stronger resistance (while it is possible). Also, bacteria do not growth in colony when you are testing for zone of inhibition (Kirby-Bauer disk-diffusion method). You can check out the following link for instruction:

https://www.sciencebuddies.org/mentorin ... p014.shtml

Michael