Sound wasteful? Well, dilution and plating is quick and easy compared to the pain of starting your experiment all over again.
Real world importance of serial dilution serial#
Then we'll end up throwing away 4 of them. ) for the serial dilution experiment, where is the dilution factor (e.g., for 10-fold sequential dilution, 10), p is the plating dilution ratio when a fraction of the dilution volume is placed on an agar plate (e.g., when 5 of the dilution volume is plated, p 20), and the ratio of plate size to colony size are a plate are a. So we might do 5 dilutions and grow up 5 plates. Every time we dilute, we'll also make a new plate to incubate. You make serial dilutions of 10-3 followed by 10-2 and 10-1 dilutions. Why do we do it repeatedly? Because we don't know how much dilution we need. You have bacteria at a concentration of 1 x 103 CFU/mL (in real life you dont. What if you are trying to count a population in the thousands or millions? You could literally have a carpet of colonies (also known as a 'confluent lawn') growing on your petri dish. For example, even 500 colonies on a petri dish would look something like this:
But we still have a problem - too many colonies to count. So, we're going to take a little bit of our culture, put it on a plate, and grow it up. Assuming you didn't stop to eat or sleep.Īnd clearly, this module is going to pick that method apart and pound it into the figurative whiteboard.įirst of all, we're going to use the Viable Plate Count method - the only method that can tell a live cell from a dead one (for a rundown on counting methods, look here).
At 1 CFU per second, that would take 11.6 days to count.
Let's say a culture contains about a million CFUs.
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