00:02
So you have a bacteria sample has a concentration of six times 10 to eight cfu per mil, colony forming unit per mil.
00:11
Show a scheme of dilution to obtain 30 to 300 colony on a plate.
00:16
So you assume that you're plating one mil of dilution on a plate, and you have to include a volume of sample and diluent and the concentration of bacteria.
00:26
So you start out with a stock that is six times 10 to the eighth power cells, or let's say cfu per mil.
00:40
Now you want to have a final dilution that will be within 30 to 300 colonies.
00:46
So i think the best bet is that you can dilute it to 60 cfu.
00:51
So this is within the 30 to 300 colony range and it's a whole number.
01:02
So then you can see if you want to dilute 6 times 10 to the 8th power to 60, then the dilution factor will be the original concentration 6 times 10 to the 8th divided by 60.
01:24
That's the final concentration.
01:26
And from there, we can calculate our dilution factor.
01:32
So from there, you can see that our dilution factor is 10 to the 7th.
01:37
So that means you want to dilute your stock to 10 to the 7th power.
01:43
So let's start with this scheme.
01:46
You start out with a stock that is, let's say, 1 milliliter.
01:52
And you add that into a tube that contains 9 milliliter of diluent so then you have a 1 to 10 dilution because you have a start 1 mil to start with and then you end up with 1 plus 9 mil or 10 milliliter in total so the volume increase 10 times that means the concentration drops 10 times so this is a 1 to 10 dilution.
02:23
Now the concentration in this dog is 10 times of this original 10 to the 8th, so it's going to be 6 times 10 to the 7th cfu per mil.
02:41
Now this is called number 1 and then you repeat this process in second tube.
02:47
You take 1 mil out from this first tube and then you add that into the second tube.
02:53
Again, contain 9 ml of the diluent.
02:57
So the second tube is 1 tenth of the first one.
03:02
But you also will have to consider the first dilution, 1 to 10.
03:06
So compared to the stock here, this is the previous dilution multiplied by the current dilution...