 Hey everybody, Dr. O here. In this video I'm going to talk about a couple different ways where we can measure both directly or indirectly how many microbes are in a given sample. So we're looking at here first is a spectral photometer. So how we use this in our lab would be when we do our ubiquity of bacteria lab where basically sends students out to sample anything they want and then we grow it and we see how much growth we had and then we also do some other things with that stuff too. Now with the spectral photometer so we would we'd grow our samples and then we can actually run them through this machine that can give you a measure of turbidity and that's the key word right. Turbid turbidity is a fancy term for cloudy but by looking at how cloudy or turbid a sample is you have a general idea of how much growth there is. Now if you want to measure that turbidity you would use this machine here a spectrophotometer. So we would actually we would have to calibrate this and determine what wavelength to use but in the end we can we put a sample of our sterile nutrient broth or triptychsoy broth whatever we're working with in the machine to calibrate it up to zero it kind of like with a scale and then take that out and put your sample in and we can determine how cloudy it is by how much light can actually travel through the sample. So as you see at the top picture here with a clear sample most of the light is going to make it through but with the second sample most of the site the light is going to be reflected or bent refracted away so a smaller amount of the light that's traveling through the machine will actually reach the detector and they can give it a general measurement of how turbid or cloudy the sample is. So that is spectrophotometry and we do use that in the lab. Here is just a direct cell count so I guess the simplest way to count bacteria is to actually count them so this reminds me a lot you know with my clinical background reminds me a lot of what's what are the hemostatometers how you can actually the same thing with measuring blood like how do you measure how do you count how many blood cells somebody has when they have millions of them in a microliter of blood will you use a special special device and you only on a microscope and you only count a very small area and then you extrapolate from that to determine the number so this here this is the same same technique but it you know slightly different this is called a Petrov Hauser chamber and you're actually just gonna have you're gonna have a known sample a known sample quantity that you put on here then you're just gonna count the cells in a given area and then you do some math and you should be doing multiple squares and averaging it out but you're gonna do the math to actually make a determination so here in the sample the example given here in the book that you count 10 cells inside that square so and we had a set the that means there was 10 cells in this sample in point 0 0 0 0 8 I believe it was milliliters so in the end you run the math and by counting 10 cells in this little chamber you would know that on average there were 1.25 million bacterial cells in a milliliter of the original sample so you take a tiny bit of the sample and count then you try to determine how big the sample the overall sample is from there so that would be a direct cell count last I'm gonna show you here would be if you this is called the membrane filtration technique this would be what you would do if you didn't if a sample was pretty dilute like let's say you're when we look at pond water or something and you wouldn't have a massive amount of microorganisms in a small sample so we need to actually concentrate it most the time we have to dilute our samples to work with them and use these serial dilutions but sometimes you have to actually concentrate your sample before you can use it so what you would do with a membrane filtration technique and the white membrane filter paper there and then you would actually as you're as you're running your liquid or whatever you're testing through this machine it's going to the filter captures the microorganisms so when you're done you take what's on this membrane filtration paper after you've run your sample through it and you and you grow that you and not you culture that and you can actually determine the cell early you can just by looking you can determine the the density of the cells in the original sample by taking the cell count that you got on from this membrane filtration paper and then divide that by the volume of liquid that we used alright so those are three ways that you can measure how much contamination or how much microbial growth you have in a sample I'll talk about a few other methods in a separate video okay have a wonderful day be blessed