Hey everybody, Dr. O here. In this video I want to talk about Griffith’s experiment from a man named Fredrick Griffith. I believe he was British so uh this would have in 1928 but actually um 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 flan Spanish Flue pandemic of 1918 that killed thirteen to fifty human beings, sis-hundred Americans in one flu season so they 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 uh bacterial infections like this organism here so that’s why he spent a decade working on this but uh so obviously that’s why it’s important an there’s never been a flu pandemic like that since the admin of the admin of antibiotics so lets that great but um amm this is also super important because it was the first evidence we have of a ahh type of horizontal gene transfer called bacterial transformation that we will get into and also um this this is what pointed us down the path to understanding what DNA was and understanding how DNA works as hereditary material so very powerful experiment it just as important in genetics as it is here in microbiology. But lets go ahead and jump in and so first you’ll see a couple terms here rough strains and heat smooth strains sorry ahhm what we are 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, ahhh the smooth strain was a virulent, very deadly, strain of streptococcus pneumonia that had a capsule round it so hopefully you remember a few chapters back that the capsule um helps an organism evade phagocytosis so um the encapsulated forms of this bacteria, Streptococcus Pneumonia, still kills 1.4 to 1.5 million human being a year so this is a vey serious deal. So, ammmm, so he was testing the tube from the strains, so lets go let go from the left all the way down the line and then we’ll see what was actually happening versus what what he thought was happening or at least um what was in play. So first we have just have the control. When you give a non-pathogenic strain that this bacterium that doesn’t have a capsule to a lab rat ummm you know our mouse here lives, it doesn’t get sick because it wasn’t a pathogenic organism; so, that’s no 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 ahhh this mouse, it also lives. What you did here is, you gave it a vaccine; right? Heat killed organisms are one type of vaccination. So, this organism is now been exposed to this ammm 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, heath killed umm pathogenic organisms. So you have thee thee dangerous organisms are dead thee non-pathogentic organism are alive and you inject it into the mouse, what happens? The mouse dies. So this is just shocking right? Because umm but the key here is what actually came out of this dead mouse was living encapsulated pathogenic strains of this organisms and that’s really what’s important here. In his last experiment, he took those organisms that came out of this dead mouse in experiment 2 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 was an example of bacterial transformation. So transformation is when an an organisms is capable of this, not all are, some are between forty and eighty organisms probably are. Umm they are able to take up what is called naked DNA from there environment. So let me go ahead and show you a quick image here so that umm, what is that, fusha circle at the told would be just a naked DNA. So, as that heat killed pathogenic strain of Streptococcus pneumonia died it fell apart, chunks of it DNA were swimming in the environment, swimming in that syringe and that thee the cell here would be a living nonpathogenic um strain of streptococcus pneumonia, but it took up that DNA, added it to its own genome and then used it. So, this, thee thee the 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 killed that mouse. They were able to extract it or take it from umm that dead mouse from experiment two uummm and transfer it into another mouse. And as you can see here, we now have living encapsulated uhhh pathogenic strains of streptococcus pneumonia; so, huge deal. This was in the late 1920,s. they didn’t know what DNA was they didn’t know how this material was being transferred, but very very important. So, we we’ll cover bacterial transformation in a separate video and that’s why Fredrick Griffith and his experiments were so important. All right, ahh you have a wonderful day. Be blessed!