 Hey everybody, Dr. O. In this video I want to talk about ID 50 and LD 50. So ID 50 is the infectious dose 50, which is the dose, the number of organisms that it would take to cause an infection in 50% of people. So it's a good measure of how virulent a microbe is, how easily it can cause infection. The LD 50, now I just so you know, I generally only think of toxins when I think of the LD 50, so it's the lethal dose 50, but technically it'd be, you know, how many viruses, how many bacteria or how many toxins would it take to kill 50% of infected people? So but for me, I think infectious dose, I think of how easily something can cause an infection. Lethal dose, I'm generally thinking of toxins. So to me, it's the best way to measure how potent a toxin is. So here we see this a picture that kind of shows the general idea that this isn't any specific organism, but you see how many organisms it takes to cause mortality in 50% of people. So that's how you figure these out. So I think it's super important as we move on here to a list to understand that these are median values, which means that if you have a very, you know, that if you have a very strong immune system, you're very healthy, a lot of stomach acid, whatever factor might come into play, it would take a much higher number for you, but someone that's malnourished and has other problems, the number would be a lot lower. So this is not, this is not an exact number by any means, it is, it's a great way to compare one organism to another. The other thing it's worth noting here, let me show you an example would be, oh, I have two mouse or other. So you have like, let's see, salmonella, enterica, the serovar, typhi there it takes, it takes about 1000 organisms to cause an infection. But the mortality rate of this typhoid fever that can be caused by this is about 10%. This right below it, the salmonella enterica serovar, typhimurium, this is going to lead to just your more quote unquote basic salmonellosis, which has a mortality rate of around 1%, you know, especially people that are getting treatment. So you notice that the infectious dose really has nothing to do with how dangerous an organism would be. All right. So just a couple of examples there, and I apologize for that aero there must have been there when I took the screenshot of this. You'll see the viruses are generally going to be pretty low, but look at like the difference between the different types of E. coli. So your E. coli 0157H7, you know, one of the most potentially dangerous forms of E. coli. The infectious dose is pretty low. This says 10 to 100. I've seen some studies that put that infectious dose between like four and five organisms, so very, very small numbers, whereas look at some of these other strains like enterotoxygenic strains of E. coli takes between, was that 10 million and 10 billion organisms to actually cause an infection. So the infectious dose basically tells you how many organisms do you have to be exposed to before you have a problem. You see like cholera down there at the bottom, that's going to be about a million, so a much higher number than some of these other ones. Okay. One more thing to think about here with infectious dose is the way in, the portal of entry. So here's an example of an organism, bacillus anthracis, which causes anthrax that has a different infectious dose depending on the portal of entry. So it takes 10 to 50 endospores to cause cutaneous anthrax with skin, with it coming in contact with your skin, inhalation anthrax, which is generally what we think of, you know, especially with it being used as a biological weapon, 10 to 20,000 endospores. And then ingestion anthrax would be 250,000 to a million endospores. So the portal of entry matters, just a couple more numbers here with the lethal dose just as a comparison. So again, it tells you how toxic a toxin is, right? How potent a toxin is or needs to be to actually lead to death or serious illness. So you see here that like botulinum toxin only takes 0.03 nanograms per kilogram, whereas the shigatoxin, which is what E. coli 0157H7, the entero hemorrhagic E. coli's would release 250 nanograms per kilogram, and then Staphylococcal enterotoxin takes 1350 nanograms per kilogram. So you're looking at a massive difference in how much of a toxin it takes to be lethal. All right. So here's the 5050, the infectious dose 50, and the LD50, the lethal dose 50. I hope this helps. Have a wonderful day. Be blessed.