 Hey everybody, Dr. Rowe here. In this video we're going to talk about the Kirby Bauer Distifusion Method, one of the most important labs that are done in the microbiology lab and obviously very important clinically as well. So, here you see an example of the Kirby Bauer Distifusion Method. So what you do is you create, I love the term, you put a confluent lawn of organisms on a plate. Now that means you're going to cover the entire plate. Use you when you as students are working with plates, we're doing streak plates or poor plates. We're trying to spread bacteria out and separate them. In this case, you want to cover the entire plate with microbes. So you spread a confluent lawn. What I have students do is rather than using a wire loop, they'll use cotton tip applicators and coat the entire surface of a plate with organisms. Now, we use known organisms, samples that I make for them. Obviously in the real world, clinically you would cover this plate with pathogens isolated from a human, from a sick person. So you cover the entire plate with organisms and then you put these discs that have known quantities of antimicrobials, antibiotics on them and then you actually will incubate them and come back and look. We're looking for these clear areas, what are known as zones of inhibition. So how large of an area around one of these paper discs is there no microbial growth? And that will tell us a few things, but just so you know, just having a zone of inhibition, it doesn't tell us everything we need to know and the size matters. So first of all, we have to standardize this. That's why we use special plates. I have another image I can show you, I'll kind of bounce back and forth. We use special plates. You see the MH there, they're called Mueller-Hinton plates. And even the thickness of the plate matters. So we use double thickness Mueller-Hinton auger plates. And then these zones of inhibition, once you actually measure them, we have to compare them to these charts. So we have data tables that say for this antibiotic and this organism, this width, this size of zone of inhibition means that it's sensitive and it works. If it's smaller than that, it might be intermediate, which means it sort of works, or it might be resistant. So there's tons of factors that go into play here. So just looking at a plate and saying this zone of inhibition is the biggest, this means it's the one that works the best is not actually true. It also won't tell you if it kills the microbes, if it's bactericidal or just inhibits their growth, bacteriostatic. So certainly there are some weaknesses here, but I find it's a pretty effective laboratory tool to teach students how some antibiotics will work better than others. Here we see just as an example of these same four antibiotics clearly work a lot better against Staphylococcus aureus than they do against pseudomonas. So that's not uncommon. Generally in the lab, we will use Staph aureus, we'll use E. coli, we'll use pseudomonas and maybe Proteus vulgaris, just kind of a random assortment. But this is pretty common here. So all right, so that is the Kirby-Bauer disk diffusion method and how it can be used in a laboratory as well as a clinical setting. I hope this helps. Have a wonderful day, be blessed.