# Calculation Bacteria - (Nov/15/2012 )

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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-

1) 55 colonies at 10^4 dilution, means 550 colonies at 10^3 dilution, 5500 (10^2), 55000 (10) or 550.000 (=5,5x10^5) colonies being not diluted. So I am guessing you missed a factor 10 somewhere?

well, if you need more bacteria.. you need to grow more bacteria.. You cant "make" bacteria yourself, you cant increase the concentration or CFU , all that you can do is dilute...

2) again, check your math.. not sure how you calculate it...
Dilute.. just dilute it...

-pito-

Hi
I am just wondering, how I can Dilute 8.5 × 10*7 cfu/ml to 1 ×10*7 CFU/ml. I asked everybody in my lab, but they are unsure about this. Could you please give an example.

Thank you

-chandch-

I calculated in this way: 85 colonies at 10*5 dilution (100 microlitres). So in 1ml 850.
Then 850 × 10*5 cfu/ml
so 8.5 × 10*7 cfu/ml (original at O.D 0.4)

-chandch-

chandch on Thu Nov 15 20:18:44 2012 said:

I calculated in this way: 85 colonies at 10*5 dilution (100 microlitres). So in 1ml 850.
Then 850 × 10*5 cfu/ml
so 8.5 × 10*7 cfu/ml (original at O.D 0.4)

Aha, I see where the extra factor 10 comes from.. you used 100µl to plate..

You have to give all the facts...

-pito-

chandch on Thu Nov 15 20:12:56 2012 said:

Hi
I am just wondering, how I can Dilute 8.5 × 10*7 cfu/ml to 1 ×10*7 CFU/ml. I asked everybody in my lab, but they are unsure about this. Could you please give an example.

Thank you

8,5 to 1 , thats just diluting 8,5 times...

You do know how to make dilutions, right?

If you take (for example) 1 ml of the 8,5 "stock" and you add 7,5ml of water..
then you end up with 8,5ml in total, containing 8,5cfu in 8,5 ml.... meaning 1cfu in 1ml

-pito-

Thank you. So If I take 1 ml of 8.5 × 10*7 cfu/ml and add it to 7.5ml of water then it makes 1 ×10*7 CFU/ml. But, if we take 1ml from that aren't we decreasing it to 8.5 × 10*6 cfu/ml. For example, If I have a stock of 2.0 × 10*8 cfu/ml and if I take a 1 ml from that add to 9ml water, i think it makes 2.0 × 10*7 cfu/ml

-chandch-

chandch on Thu Nov 15 21:07:45 2012 said:

Thank you. So If I take 1 ml of 8.5 × 10*7 cfu/ml and add it to 7.5ml of water then it makes 1 ×10*7 CFU/ml. But, if we take 1ml from that aren't we decreasing it to 8.5 × 10*6 cfu/ml. For example, If I have a stock of 2.0 × 10*8 cfu/ml and if I take a 1 ml from that add to 9ml water, i think it makes 2.0 × 10*7 cfu/ml

yes, in your example, you diluted it 10 times...

But this "But, if we take 1ml from that aren't we decreasing it to 8.5 × 10*6 cfu/m" , I dont get it.

You mean, if you take 1 ml of the 8.5 × 10*7 cfu/ml and add that to 9ml of water? or?

-pito-

Yes, If I take 1 ml of the 8.5 × 10*7 cfu/ml and add that to 9ml of water, Is it 8.5 × 10*6 cfu/ml?
So to get 1 ×10*7 CFU/ml, do I need to add 1ml of 8.5 × 10*7 cfu/ml of to 7.5 ml of water?

Thank you

-chandch-

chandch on Thu Nov 15 21:53:17 2012 said:

Yes, If I take 1 ml of the 8.5 × 10*7 cfu/ml and add that to 9ml of water, Is it 8.5 × 10*6 cfu/ml?
So to get 1 ×10*7 CFU/ml, do I need to add 1ml of 8.5 × 10*7 cfu/ml of to 7.5 ml of water?

Thank you

If you take 1ml of the 8.5 × 10*7 cfu/ml and add that to 9ml of water, you will indeed have 8.5 × 10*6 cfu/ml?

So yes, you need to take 1ml of the 8.5 × 10*7 cfu/ml and add this to 7,5ml of water to get 1 ×10*7 CFU/ml

-pito-
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