When you re thinking about dilution, it helps to simplify your actions into dilution factors.
Overall dilution factor.1.1.01.0001 Multiply by the inverse I think I have the answer: 48 1/0.0001 480,000 CFUs per mL I did a series of dilutions as follows: 1 mL added to 9 mLs water 1 mL added to 99 mLs water.
Anyone can eat a soup that has 90 peas per liter.
In fact, even with our absolutely pdf book reader software flawless technique, the best we can say is that there are between 182,500 and 183,500 cells.
You definitely need at least 1 dilution, in case Frank is somewhere in the 300 or 400 per mL range.If Frank has 300 colonies in a 1/10th dilution, he has 3000 actual cells per mL, and that would be fatal.But on the other hand, how can we avoid.Once again, here s an applet to practice finding the total dilution scheme, regardless of how the dilution scheme is expressed - as directions, as fractions, or as decimals.But remember that diluting and sampling is bascially a random process, and imagine the havoc caused by one extra CFU ending up in your pipette - suddenly you estimate the population as 60,000 rather than 50,000, and you re off.But this time, going from 900 to 90 peas per liter required only a ten to 1 dilution.How many bacteria were in the original container of food.So That s a dilution factor of 100.Voila, soup with only 90,000 peas per liter.So you can see that the 30 to 300 guideline is really a compromise between countability and error.
With a known concentration to make a more dilute solution.
In other words, not trillions, not millions, but hundreds of billions.
1 mL - mL water, then 1 mL - mL water.Why do we dilute.Another hint : Multiply the number found by the reciprocal of 1/10,000 I think I have the answer: about 490,000.So, now we finally have all the pieces of serial dilution assembled: Dilute Calculate dilution factor Plate Repeat To make things easier, the standard operating procedure is to go by factors of 10, and to do about 5 or 6 plates altogether.Below are a few unusual situations things do go wrong, of course, and you should be able to recognize that.For example, even 500 colonies on a petri dish would look something like this: What if you are trying to count a population in the thousands or millions.I need a hint : The students took a 1/10,000 sample, so what do they need to multiply.Then I make 4 more 1/10 dilutions, plating each one in turn.