 Hey everybody, Dr. O here. This video I want to cover the autoclave, so I left the whole table up here because we did do a comparison of moist and dry heat, but we're just going to focus on the autoclave in this video. So, a little tiny bit of history, autoclave was developed by a man named Charles Chamberlain who was working in Louis Pasteur's lab all the way back in 1879. So the simplest way to think of an autoclave is it's a big pressure cooker, right? There are even industrial sized autoclaves that you can maybe drive a small car into called retorts. So the whole principle behind an autoclave is that if you increase the pressure, water boils at a higher temperature. So really, really key numbers, I'm sure you'll be asked to know, with the autoclave, a typical autoclave is running, is going to boil water and turn into steam at 121 degrees Celsius versus 100 at sea level for 15 minutes at 15 pounds per square inch. So as the pressure goes up, the temperature would go up. So 121 degrees, 15 minutes, 15 psi, those are critically important numbers with an autoclave. Autoclaves work by the steam will actually, like other forms of moist heat, will denate your proteins and alters membranes. But the key here is that autoclaves are used to sterilize in ways boiling water never would be able to because the temperature is high enough to do so. The other key with autoclaves is they're designed or used when you need to kill spores. So spores and endospores will be killed in autoclaves in ways they won't be killed with other methods. That's why I always tell students in my labs that the autoclave is the most important tool that we have. We sterilize everything before they use it. So they're working with sterile, non-contaminated products, and we sterilize everything after they use it to turn the biohazardous waste they produce into garbage, right? So we actually had both autoclaves broke down one time and for weeks our lab was completely hampered with contamination, all sorts of problems. So it was really, really a struggle until we could get some more autoclaves purchased. So autoclaves are wickedly important. All right. Let me show you what an autoclave looks like. So there are two different types of autoclaves, not a huge deal, but most of the time you're going to be using a, like I said, they're just basically a large pressure cooker. So you have a sealed container where the pressure can be controlled. But there are two types. There's the gravity displacement autoclave, which is the ones that we use in our lab anyways, which means that steam is going to enter into this chamber. And as steam enters into the chamber, it's going to force the air out. So that's why it's called gravity displacement. So the air is going to be forced down and out of the chamber. Once all the air is gone, then basically the container will be sealed. And now it's full of pressurized steam. There are also pre-vacuum sterilizers, not a big deal, but they suck the air out first and then add the steam. So maybe more effective, definitely quicker. But that's definitely not a big deal. So that's how the autoclave works. Now the second key thing with the autoclave besides 121 degrees, 15 minutes, 15 PSI is how they work. Steam is what's killing and sterilizing the organisms inside this chamber. Steam must come into direct contact with what's in the chamber. So you can't have sealed containers. You don't want air pockets forming in any of your containers. So that is like the biggest weakness of an autoclave. The steam must come into direct contact. So one exception to this rule of 121 degrees. So we keep saying that autoclave sterilized. I think that's a fair word. But this autoclave, the autoclave, the way that we use it, would not destroy prions, infectious proteins that lead to things like mad cow disease, wheat-filled yacob disease, et cetera. So when they first learned about prions, the only way we knew you could kill them would be concrete blast furnaces burning at something like 1,400 degrees Fahrenheit. But now there are autoclave protocols that appear to work. And there are other things you can do, too, like using enzymes, et cetera. But if you were trying to make sure that you destroyed prions in an autoclave, last numbers I've seen are using 132 to 134 degrees for up to an hour, rather than 121 degrees for 15 minutes. But even then, I'm not 100% certain that that works. So prions are an exception to the rule. Just thought it'd be kind of interesting to tell you that. All right, so how do you know an autoclave is going to work? So here we see autoclave tape. It's the simplest way to use it. That black stripe will form on that piece of tape. If it reaches the temperature you need, the 121 degrees. The problem is we can't look at this and say, okay, we sterilize what was inside the autoclave because it doesn't tell us how long the autoclave reached that sterilizing temperature. If you really want to know if an autoclave is working, you use what are called biological spore tests, where you put paper or liquid or something that has a really hardy spore in it. Geobacillus stearothermophilus, I don't know how to say it very well, is the best example because it appears to be the most heat-resistant spore that we have. So if you can kill those spores in an autoclave, you know you're killing the spores you have to worry about. Okay, that's an autoclave, wickedly important, because it's an essential ingredient in all microbiology labs. So steam kills. All right, have a wonderful day. Hope this helps. Be blessed.