How can you count bacteria and what is the procedure?

Question

I want to know how to count bacteria to make my research more reliable... please help me...

Answer 1

Ms. K is right. Do a serial dilution...you should have a general idea of the approximate number of colonies you would get with your original sample (maybe somewhere around 10 to the 9). So, in order to be able to count the colonies on an agar plate, you probably want a number around 100 (which is 10 squared). So, you need to dilute your solution down by a factor of 10 to the 7. Sounds hard, but its really not.

Here's what you do: for your first dilution, dilute by a factor of 100. To do that you take a certain amount of your initial sample (say 1 mL) and add that to 99 mL dilution solution. Do this two more times. That will dilute your solution by a factor of 10 to the 6. For your final dilution, you just want a ten fold dilution. To do this add 1 mL of your solution to 9 mL's of your dilution solution. Then all you have to do is plate a few of the different solutions and count the colonies!

Sounds rather complicated, but really its not. Did this plenty in my microbiology class.

Answer 2

Do serial dilutions of the bacteria and put known amounts of the solution on to a nutrient agar plate. Each bacteria cell will grow into a colony in few days. Count the colonies. You can determine the density of the bacterial cells this way. Just back calculate to find the original density before you did the dilutions.

This is assuming you have bacteria that will grow on agar (some don't)