 Traffic. Hey everybody, Dr. O here. This video we're going to talk about temperatures effect on the growth of microorganisms. So you're going to see here we're going to talk about these four categories and I'm going to add a fifth one as well. So just looking at this chart we have psychrophiles, which are going to be your cold temperature loving organisms, mesophiles, some call them mesophiles. These are moderate temperature loving organisms and these are going to be the most important. Thermophiles are heat loving organisms and then hyperthermophiles or some people call these extreme thermophiles are going to be extreme heat loving organisms. So and then we're going to add a category right there between between psychrophiles and mesophiles called psychrotrophs, which is a term that food microbiologists use. So okay, so first of all, just look at these different ranges. So most most organisms have about a 30 degrees Celsius window where they can grow. So if you look at any one of these, let's say mesophiles, for example, what is that orange or yellow, whatever it is on the far left would be that it's minimal growth temperature on the far right would be its maximal growth temperature and then the peak at the top would be its optimal growth temperature. So the reason we care so much about them as the files is their optimal growth temperature is 37 degrees Celsius. Reason that's so important is because that's 98.6 degrees Fahrenheit. So obviously organisms have evolved and adapted to prefer the temperature of their hosts and it shows you why we have to care so much about these. So a couple more things before we jump into specifics here, you'll notice especially with those mesophiles and all of them really notice that this is not an upside down V, right? You've got the from minimal to optimal growth temperature you see kind of a gradual change but then it starts to drop off when you reach that maximum growth temperature. And that's because at least we believe that that's where critical enzymes that are needed for growth are going to be inactivated by the temperature. So the high temperature basically will denature or destroy the protein based enzymes and that's why you see the growth start to fall off there, okay? All right, so really let's get the ones out of the way that really don't matter. Thermophiles, so these heat-loving organisms, the reason we don't care about them is because they don't grow. They really can't grow below 45 degrees Celsius. So they're not going to cause, they're not going to cause human disease. They're not going to be pathogens and they're really not going to lead to any issues with foods boilage. I mean they might but not as far as making you sick. They're not a health concern. So like for example, some thermophiles will survive the industrial canning process. So there can be thermophilic bacteria in your canned goods and they can even spoil your food but they're not going to lead to food poisoning. So thermophiles, now if I gave you a good example, a good example here would be organisms that live in compost piles. They love the temperature of sunlit soils. So if you're a gardener like myself and you do any composting, specifically what would be called hot composting, you rely on thermophilic organisms. I actually buy a container. It's about the size of a cereal box of a starter culture that I use when I start a new compost pile to add these thermophilic bacteria. Hyperthermophiles, I think of them, they basically live in hot springs or deep sea thermal vents, things that are associated with volcanic activity. They can grow even as high as the highest recorded one, I believe is 121 degrees centigrade or Celsius. So we don't really worry about them because our primary concern is what makes us sick and what causes food poisoning, right? So the two we're going to focus on here then will be the mesophiles and the sycrophiles. So the sycrophiles, they're going to grow relatively well in the refrigerator and even freezer temperatures. So the sycrophiles, really, I like to think about the freezer. So first of all, I said relatively well because nothing grows well in the freezer. These just grow well in the freezer compared to other organisms. So given enough time, sycrophiles can lead to changes of your food even at the freezer temperature. But they're not a very big deal. The mesophiles, these are going to be almost all your human pathogens and because mesophiles will grow at body temperature and room temperature, they can lead to some foodborne illness and food spoilage as well. So for mesophiles, think human pathogens. Like when we use an incubator in the lab, it's almost always set at 37 degrees Celsius because that's where your pseudomonas and E. coli and staff and strep all these organisms that we care about grow at that temperature. So the mesophiles think human disease, pathogens. Now we've got to add this extra category. So again, I'll show you in the video where it is. But between sycrophiles and mesophiles, this is a term that food microbiologists use called psychrotrophs. And I wish it was on this chart, but it isn't. So psychrotrophs, these are much more important than sycrophiles because these are going to lead to a lot more spoilage in the refrigerator. So they lead to low temperature food spoilage. They can grow in the refrigerator. So if you're looking at foodborne illness at lower temperatures, like the refrigerator and even in a cool room, it would be the psychrotrophs that we're primarily concerned about. So it's kind of, there's obviously some overlap here as far as which organisms cause food spoilage. It would be both the psychrotrophs, especially at lower temperatures, but the mesophilic organisms would cause food spoilage at room temperature as well. But just for all intents and purposes, if you're in one of my classes, mesophiles think pathogens, human disease, psychrotrophs think food spoilage. Okay, so those are the different groupings of organisms based on the temperature they live at. So that is temperatures effects on growth. Have a wonderful day. Be blessed.