 Hey everybody, Dr. O. In this video, we're going to cover the bacterial growth curve. So you see it's got four different steps, the lag phase, log phase, the stationary phase or the death phase. So we'll go through each one of these. All right, so let's start with the lag phase. So you notice it's a horizontal line because we're not seeing a logarithmic change in the population of bacteria. So there's no increase in the number of living bacterial cells, but doesn't mean they're not doing anything. This is very important. So a couple of examples. I think of it like if you're a factory and you're going to start churning out cars, for example, you have to build the factory first. So all the preparatory work is going into play. Once the factory is built, then you'll start churning out cars, right? So another example I think of is interphase with the cell cycle during mitosis. So interphase is the cell is not dividing, but it's really busy because it's preparing to divide. DNAs being replicated, organelles are being replicated, et cetera. So those are just examples just because you don't see any increase in population doesn't mean nothing's happening here. It's definitely not like a dormant phase. So during the lag phase, the bacterial population is not changing rapidly, but it's preparing to do so. They're synthesizing enzymes and metabolic products that are going to be needed to reach the next step, which is the log phase. So it's called the log phase because we see exponential growth or logarithmic growth. The reason that we see this logarithmic growth as a straight line is because the generation time is now constant. So the generation time is how much time it takes for an organism to divide and then for the population to double. So some organisms like E. coli would have a generation time that's really low, like 21 minutes, 20, 21 minutes, others are going to be much longer. So this log phase is when the cells are actively doubling and increasing in number. So the key thing here is that if this were to continue forever, we would see an unbelievable number of bacteria. We'd be living on a planet with a bacteria a mile deep. So if you take a single cell that has a generation time of 20 minutes in 25 and a half hours, that cell could become a pile of organisms, a pile of bacteria that weighs 80,000 tons. So it clearly doesn't happen. So lag phase, no increase in population, but preparing to increase in population. Log phase, this explosion in growth. Then we reach the stationary phase. I often call this the plateau phase, but stationary phase is just fine. Just think here, births equal deaths. So there's still plenty of cells that are being born right there dividing, but the cells are starting to die here as well. So why don't we see this log phase continue? Why don't we get to a pile of bacteria that weighs 80,000 tons? That's because it's not always known, but most of the time the reason this happens is because we run out of space or run out of food is a big one. We poison the environment, right? These microbes are going to spew their waste products into the environment. So they're out of food. They're making the environment toxic with their waste products. And many of these metabolic waste products are going to change the pH. So maybe the pH in the environment has now changed, which is keeping these cells from growing at the same rate. So thankfully that does happen. So that's the stationary phase where births now equal death. Then we reach the death or decline phase where you'll see a logarithmic decline in the population. So the population's going to die once you're out of space, out of food, you know, too many waste products. It's going to die almost as fast as it was quote unquote born. So that's going to be the death phase. So both the log phase and the death phase are going to see logarithmic changes in population. So this death phase can lead to really in a relatively short period of time, the entire population can disappear or just a handful will be left. Or for some organisms, this process takes a lot longer. So the entire process from lag phase to the end of the death phase can take really just a matter of days. But with some organisms, it's years. Which means that some contaminated areas would have microbes that are still hanging around at the end of this death phase even years later. All right, so that is your bacterial growth curve. So lag phase, log phase, stationary phase where births equal death and the death or decline phase where we see a logarithmic decrease in population. Okay, I hope this helps you understand how bacteria grow. Actually, let me say one last thing that is actually really important. The log phase when the population of bacteria is exploding, that's actually when they're most susceptible to our treatments. Which makes sense, right? If you're churning out new cells and you need new cell walls for those cells and penicillin is stopping those cell walls from being formed, you're going to see why there's going to be more damage there. Or if you're using an antibiotic, for example, that inhibits protein synthesis. If you're churning out new cells, you're going to need a whole lot of protein. So that's actually a very important thing, I'm glad I remembered to say it. So during that log phase is going to be when your microbes, when the bacteria that we're talking about here are most susceptible to the majority of our treatments, the majority of our antibiotics. All right, hope you guys have a wonderful day. Be blessed.