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## Bacterial Calculation

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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### Bacterial Calculation

Hi
I am trying to calculate colony forming units calculation. I cultured bacteria overnight (15ml) and did O.D reading at 0.4 and did serial dilution (10*1 to 10*9) and I got 55 colonies at 10*4 dilution. So I got 5.5 × 10*6 cfu/ml (original, if I am right). But I need 1 ×10*7 CFU/ml (for my experiment). How can I Increase it it. Please give example calculation.

2) I also cultured bacteria overnight (15ml) and did O.D reading at 0.4 and did serial dilution (10*1 to 10*9) and I got 85 colonies at 10*5 dilution. So I got 8.5 × 10*7 cfu/ml (original, if I am right). But I need 1 ×10*7 CFU/ml (for my experiment). How I can I reduce it down?

Thank you
chandch
Garter

Posts: 1
Joined: Thu Nov 15, 2012 6:00 pm

if you get 55 colonies at 10^4 dilution, shouldn't you have 5.5 . 10^5 CFU?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.

JackBean
Inland Taipan

Posts: 5694
Joined: Mon Sep 14, 2009 7:12 pm

Check out this serial dilution calculator for the future. Automated and flexible. [link]
Last edited by JackBean on Sun Jan 13, 2013 12:00 pm, edited 1 time in total.
Reason: link removed
vanwa71
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Posts: 3
Joined: Sun Jan 13, 2013 1:05 am

### Re: Bacterial Calculation

Hallo,
You don`t need a serial dilution calculator ... seriously.
If you get 55 colonies at a 10^4 dilution, then you have 5.5*10^5 cfu/mL (in case you used an aliquot of 1 mL). If you count 85 colonies at a 10^5 dilution then it`s 8.5*10^6 cfu/mL, which is already close to the concentration you need. To get more precise values, you could grow the cells to a higher density than you actually need and dilute them to the desired concentration.
EnricoPallazzo
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Joined: Sun Dec 04, 2011 6:13 pm

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