## 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.

zhar2
Garter
Posts: 5
Joined: Thu Jan 07, 2010 3:55 pm

### Cell number from dilution factor.

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.

JackBean
Inland Taipan
Posts: 5694
Joined: Mon Sep 14, 2009 7:12 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)
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

zhar2
Garter
Posts: 5
Joined: Thu Jan 07, 2010 3:55 pm

### Re: Cell number from dilution factor.

So ou just multiplied colonies by dilution factor?

JackBean
Inland Taipan
Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm
Sure
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

mkwaje
Coral
Posts: 146
Joined: Mon Jul 03, 2006 2:48 am
Location: Philippines

### Re: Cell number from dilution factor.

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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