Science Buddies: "Ask an Expert"

Hi,
I am doing a science fair experiment comparing the effectiveness of penicillin vs. the T4r bacteriophage in killing E. Coli. I am collecting data by measuring the total area of the all the zones of inhibition in each plate. I used the Kirby Bauer method to get zones of inhibition for the penicillin disks, but was confused when some zones were clear and some were a solid whitish color. I was going to write about why this might have occurred in my paper but could not find information online, and my paper is due as soon as possible. Any help would be much appreciated

Thanks so much!

Hi Kolbe,
When you say a solid whitish color, do you mean that the agar has turned white? I have some experience with phages, but I really need to see pictures of your plates, could you post some? Hopefully we can get to the bottom of this.