 Hey everybody, Dr. O here. In this video I want to talk about Griffith's experiment from a man named Frederick Griffith, I believe he was British. So this would have been done in 1928, but actually he had been working for at least a decade to try to understand bacterial pneumonia, specifically the microorganism streptococcus pneumonia. And this ties back into the Spanish flu pandemic of 1918 that killed 30 to 50 million human beings, 600,000 Americans in one flu season. So they understood that many of the people that died from that flu actually weren't dying from the flu virus. They were dying from secondary bacterial infections like this organism here. So that's why he spent a decade working on this. But so obviously that's important. And there's never been a flu pandemic like that since the advent of antibiotics. So that's that's great. But this is also super important because it was the first evidence we have of a type of horizontal gene transfer called bacterial transformation that we'll get into. And also this, this is what pointed us down the path that led us to understanding what DNA was and understanding how DNA works as hereditary materials. So very powerful experiment. This just as important in genetics as it is here in microbiology. But let's go ahead and jump in. So first you'll see a couple of terms here, rough strains and heat, smooth strains, sorry. What we're looking at here is what he would have called the rough strain would be a non-pathogenic non-virulent strain of streptococcus pneumonia that didn't have a capsule around it. The smooth strain was a virulent, very deadly strain of streptococcus pneumonia that had a capsule around it. So hopefully you remember from a few chapters back that the capsule helps an organism evade phagocytosis. So the encapsulated forms of this bacteria, streptococcus pneumonia, still kill 1.4 to 1.5 million human beings a year. So this is a very serious deal. So he was testing the two different strains. Let's go from the left all the way down the line and then we'll see what was actually happening versus what he thought was happening or at least what was in play. So first we have just the control. When you give a non-pathogenic strain of this bacteria that doesn't have a capsule to a lab rat in our mouse here, it lives, doesn't get sick because it wasn't a pathogenic organism. So that's no shock there. Experiment number one, if you take the deadly pathogenic strain of streptococcus pneumonia that does have a capsule and you kill it with heat and then give it to this mouse, it also lives. What you really did here is you gave it a vaccine, right? Heat killed organisms are one type of vaccination. So this organism has now been exposed to this, this mouse has been exposed to this organism has developed immunity against it. So really experiment one is an example of a vaccine. Experiment two, if you take the non-pathogenic organism and mix it with dead heat killed pathogenic organisms, so you have the the dangerous organisms are dead, the non-pathogenic organisms are alive and you inject it into the mouse, look what happens, the mouse dies. So this is just shocking, right? Because, but the key here is what actually came out of this dead mouse was living encapsulated pathogenic strains of this organism and that's really what's important here. Then his last experiment, he took those organisms that came out of this dead mouse from experiment two and put them in another mouse and it got sick and it died. So what actually happened here was, so he knew that something, some sort of material was transferred from the dead organism to the living organism. So what really did happen here is an example of bacterial transformation. So transformation is when an organism that's capable of this, not all are, some are between 40 and 80 species of organisms probably are, they're able to take up what's called naked DNA from their environment. So let me go ahead and show you a quick image here. So that, what is that, fuchsia, a circle at the top would be just a piece of naked DNA. So as that heat killed, pathogenic strain of streptococcus pneumonia died and fell apart, chunks of its DNA were swimming in the environment, swimming in that syringe. And the cell here would be a living non-pathogenic strain of streptococcus pneumonia, but it took up that DNA, added it to its own genome and then used it. So this, so the purplish organism here was able to pick up the ability to grow a capsule and it happened inside that mouse, that organism became a pathogen and then killed that mouse. They were able to extract it or take it from that dead mouse from experiment two and transfer it into another mouse. And as you can see here, we now have living encapsulated pathogenic strains of streptococcus pneumonia. So huge deal. This was in the late 1920s. They didn't know what DNA was. They didn't know how this material was being transferred, but very, very important. So we'll cover bacterial transformation in a separate video, but that's why Frederick Griffith and his experiments were so important. All right. You have a wonderful day. Be blessed.