 I want to talk about, to me, one of the most important topics in microbiology, at least for how things are happening moving forward clinically, and that is the idea of quorum sensing. So quorum sensing is a critical way that microbes communicate with each other. So think of it like chemical messengers, so think about like our hormones, right? Your individual cells are talking to each other using hormones. Well, these are individual single celled organisms that are using these chemical messengers to communicate in a group. So maybe it'd be a better example would be to say like pheromones, but not a big deal. So the main reason that quorum sensing is important is it's basically how microbes count, how many other microbes are around. So this would be a couple of critically important examples would be biofilm formation. So when you've reached a certain cell population or cell density where an actual physical biofilm should start to form in this environment, it'll be because those cells are all releasing these compounds called autoinducers, these chemical messengers, and I don't care if you know what they are, but these autoinducers reach a point where there's enough of these organisms raising their hand and saying, I'm here, I'm here, I'm here, and then it'll actually turn on gene expression that will lead to the production of a biofilm. So but the most important reason to understand quorum sensing is that a lot of pathogenic bacteria will not actually start to produce what their virulence factors, the things that make them cause illness and potentially death until they know there's enough organisms around to overwhelm the host immune system. So a dangerous pathogenic organism is not often dangerous until it knows there's enough of its buddies around to actually do anything. So on the left hand side you're seeing, yes, these chemical messengers are being released, but if there's not a certain concentration of cells, nothing will happen. The genes won't actually be expressed. So a small population of a pathogen doesn't have to be dangerous. That's why we have what are called infectious doses. How many of a pathogen does it take to actually cause a problem? Or this might be why you have a pathogen hiding in your body doing nothing, but when it reaches a certain population, a certain cell count, that's when you see it becoming dangerous. So a couple quick examples. Again, I already told you that biofilms use quorum sensing to know how they should be building a biofilm. On the right you see this bioluminescence. So there's an organism called Vibrio fissurei that's been very well studied. We talk about in other places in the class where it actually is bioluminescent, but only when they reach a certain population. So that's not a huge deal. So why do I see this being so significant? Well, if there are pathogens, like we know that manabox are being taken off the market faster than they're being put on. Clearly, there are organisms that we are having a very hard time killing. So what if we don't have to kill them? What if we can interrupt how they communicate? So imagine having a very, very dangerous microorganism, a very dangerous bacteria, and we can't kill it. But rather than killing it, we use what are called quorum sensing inhibitors. We use compounds that actually block their communication. So we block their cell signals or whatever. And then you've got all of these pathogenic microbes around that don't know that they're amongst their friends. So they don't ever turn on these virulence factors. So we might be able to allow our immune system to come in and mop these things up without them, hopefully, thankfully killing us, right? So then also we could use things that stimulate quorum sensing, too. So we could actually use quorum sensing drugs or compounds to stimulate growth in some areas and then hopefully control growth or virulence in others. All right, so we'll go back to the first image. That is quorum sensing, how these microbes communicate. And then I gave you the three key examples of when we see them in use in nature. Okay, have a wonderful day. Be blessed.