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Cell number from dilution factor.

About microscopic forms of life, including Bacteria, Archea, protozoans, algae and fungi. Topics relating to viruses, viroids and prions also belong here.

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Cell number from dilution factor.

Postby zhar2 » Thu Jan 07, 2010 3:57 pm

How can i find bacteria concentration from dilutions?
If i got 2 dilutions of 10-5 & 10-6 (volume of 0.1 ml) & 36 colonies for 10-5 & 7 for 10-6.
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Postby JackBean » Thu Jan 07, 2010 6:57 pm

From one you get 3.6*10^6 and from second you get 7*10^6. If you have only these two numbers, you don't have much more choices, than to make average... (but the mistake will be pretty big)
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Re: Cell number from dilution factor.

Postby zhar2 » Thu Jan 07, 2010 9:29 pm

So ou just multiplied colonies by dilution factor?
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Postby JackBean » Thu Jan 07, 2010 9:33 pm

Sure
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Re: Cell number from dilution factor.

Postby mkwaje » Sat Jan 30, 2010 10:25 am

Actually using the old method of bacterial enumeration. you have to consider only the plates containing colonies between 30-300.. For fungal plates, they adjusted it to 25-250... At these colony numbers, there is a higher chance of getting the correct CFU. Discard the plates with lower than 30 or higher than 300 since the counts you will obtain if you use the formula will just be estimates.

cfu/ml = ave. # of colonies x DF
............total volume plated


Therefore, using only the 10^-5 dilution (since it has 36 colonies [falling between 30-300]), you'll have

cfu/ml = 36 x 10^5 = 3.6 x 10^7 CFU/ml
...............0.1

I didn't even need my calculator for this...

Good luck!
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