Dear Ozge,

For calculating the colony forming unit bacteria, please see the following text:

colony-forming unit (CFU or cfu) is a measure of viable bacterial or fungal cells. In direct microscopic counts (cell counting using haemocytometer) where all cells, dead and living, are counted,but CFU measures only viable cells. For convenience the results are given as CFU/mL (colony-forming units per milliliter) for liquids, and CFU/g (colony-forming units per gram) for solids. CFU can be calculated using miles and misra method, it is useful to determine the microbiological load and magnitude of infection in blood and other samples.

Example:

Calculate the number of bacteria (CFU) per milliliter or gram of sample by dividing the number of colonies by the dilution factor The number of colonies per ml reported should reflect the precision of the method and should not include more than two significant figures.

The CFU/ml can be calculated using the formula:

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

For example, suppose the plate of the 10^6 dilution yielded a count of 130 colonies. Then, the number of bacteria in 1 ml of the original sample can be calculated as follows:

Bacteria/ml = (130) x (10^6) = 1.3 × 10^8 or 130,000,000.

CFU/mL Practice Problems - CFU/mL Calculation Examples

Problem 1:

Five ml of Bacterial Culture is added to 45 ml of sterile diluent. From this suspension, two serial, 1/100 dilutions are made, and 0.1 ml is plated onto Plate Count Agar from the last dilution. After incubation, 137 colonies are counted on the plate. Calculate CFU/mL of the original Sample?

Answer:

First thing we need to know is the Dilution Factor, or how much the original sample is diluted:

here Initially 5mL in 45mL = Final Volume / Sample volume = 50/5 = 10.

Then two serial dilutions of 1/100.

Total Dilution Factor = 10 * 100 *100 = 10^5

CFU/mL = cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

= (137 * 10^5)/0.1

=1.37*10^8

So Total colony forming units = 1.37*10^8 CFU/mL

Converting CFU/mL to Log value

For example,

Total colony forming units = 1.37*10^8 CFU/mL and you want to convert it into Log value,

Just take Log(CFU/mL)

Here, log (1.37*10^8) = 8.13924922.

Useful for expressing log reduction of microbes / biologic log reduction.

For illustration of the figures in this article, please use the following link:

http://technologyinscience.blogspot.co.il/2011/11/cfu-colony-forming-unit-calculation.html#.VpF-W_krLIW

Hoping this will be helpful,

Rafik

Basically, you have to measure it by plating out the various dilutions of the glycerol stock on agar plates made in growth medium and counting the colonies.

I think there is some difference between directly counting the glycerol stock and the activated bacteria (after 2 or 3 times culture in broth). So it's always recommended to activate the bacteria at the begining with broth culture to get the best result.

Dear Ozge

you can calculae CFU by:

1. make a seri dilution (make the specific bacterial concentrations).

2.inocolum 10µl of each bacterial concentration on non selective agar medium like BHI agar.

3. put palte in 37 C for overnight.

4. the plate that is related to the concentration af bacteria that is you can count onplate.

5. number of colny * 10* selective consentration.

Maybe İ am mistaken but we probably missed part with McFarland value. Which McFarland is equal to for example 3*10^6 CFU? 

 hi guys...i have 1 question regarding MIC (minimum inhibitory concentration ) for antibacterial assay...lactobacillus vs pathogens..to analyse this assay..what is the suitable unit of lactobacillus concentration to get the IC50?log cfu /ml or microlitre/ml?

Hi. Thanks for the information. I have a question. I the CFU is uncountable, how can I to represent with log. I need to show differences between CFU. Thanks!

Yes, this is a problem. If you get zero colonies, it can't be represented on a log scale. What people tend to do in this situation is to work out the lower limit of detection of the assay, and represent a zero result as being at that value. For example, if the lower limit of detection is 100 cfu, zero colonies is represented as 2 on the log10 scale.

The origin of the lower limit of detection is when there is a limit to the volume of sample that can be plated, which is only a portion of the sample. If you can only plate 100 µl out of a 10-ml sample (1/100), then if the whole sample had 100 cfu, you would only get 1 colony (on average).

It is important to be explicit about the lower limit of detection, and how such low cfu counts are being handled when describing the methodology.

Thanks Adams, your answer was useful. I get one colonie in all plate, so, the solution is same, with the lower limit of detection?

I have another question, for the statistical analysis. I dont know what is the most arpropriate transformation, whit log, log10, log n or log taylor. I found all in differents papers.

Thanks a lot!

Here is a link to the US FDA guidance on statistical analysis of cfu data;

https://www.fda.gov/ScienceResearch/FieldScience/ucm174294.htm

It recommends the use of the geometric mean.

Thank you!

thanks

Hi,

Colony Forming Unit Calculation:

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

https://www.youtube.com/watch?v=jdnOjoOO6qY

Serial Dilution of Bacterial Culture:

http://technologyinscience.blogspot.com/2014/08/serial-dilution-of-bacterial-culture.html

http://technologyinscience.blogspot.com/2011/11/cfu-colony-forming-unit-calculation.html

https://www.youtube.com/watch?v=jdnOjoOO6qY

hi. Thanks for the information. I have a question. Can any of you give an example how can I transfer the number of colonies to cfu/gm?

Me, the same. I m not clear about how to calculate CFU/g .  My work, I calculate by

Example. 

10g of silage was placed into 90 ml water. The solution was serial diluted .

. then 0.01 ml of the dilution was spread onto the agar plate.

the number of fungi colonies that I obtained are 50 colonies at 1/100. 

CFU/ml = 50 x 100/ 0.1 = 50000 CFU/ml 

--Dry weight of 10 g silage is 4.53 g

--then  50000 CFU/ml /4.53 g =11035 cfu/g 

it is correct? please help me...

but I read from the other book but it is different. So, I m not sure which one is correct. 

--You can read about the formula calculation from below link 

https://books.google.co.th/books?id=YGUcnCOidEgC&pg=PA274&lpg=PA274&dq=soil+AND+dry+weight+AND+CFU/g+AND+serial+dilution&source=bl&ots=hiEuokwbRU&sig=BY34s0IX1w5vZhkrbf22TG5AzSI&hl=th&sa=X&ved=0ahUKEwjhiYeLxurSAhWLNY8KHTmOC0kQ6AEIRjAF#v=onepage&q=soil%20AND%20dry%20weight%20AND%20CFU%2Fg%20AND%20serial%20dilution&f=false

https://books.google.co.th/books?id=ZTJsbXsikagC&pg=PA345&lpg=PA345&dq=moist+soil+dilution+AND+CFU/g&source=bl&ots=VeIwzS3VT3&sig=1PjSBH6phb4M_nT3_8uCtZtYSjs&hl=th&sa=X&ved=0ahUKEwioo-OJxJXTAhVIt48KHdmjBRs4ChDoAQgXMAA#v=onepage&q=moist%20soil%20dilution%20AND%20CFU%2Fg&f=false

How to calculate CFU/g (moist soil)?. Available from: https://www.researchgate.net/post/How_to_calculate_CFU_g_moist_soil [accessed Apr 9, 2017].

How can we calculate the number of bacterial cells in nutrient broth with spectrophotometer.

The usual estimate is that OD600=1 (1 cm path length) represents on the order of 109 CFU/ml. This is a rough estimate, however. It needs to be calibrated by plating serial dilutions of the culture on agar and counting colonies.

http://www.fedegari.com/wp-content/uploads/2016/07/ST19_EBook_F0-What-it-means-How-to-calculate-it-How-to-use-it.pdf

Thanks Rafik for your valuable information

@Emin please note the McFarland number and the cell counts are variable for any given bacteria depending on their morphology. But rough guide lines are available.

Approx. cell density (1X10^8 CFU/mL)

MF at 600 nm Ab

1.5 - MF No0.5

3.0 - MF No.1

6.0 - MF No.2

9.0 - MF No.3

12.0 - - MF No.4

Hi

I think can use spectrophotometer

thanks

issam

You can calculate it in different methods:

1- standard plate count using suitable medium for cultivation then counting the yielded colonies.

2- direct microscopic count using haemocytometer.

3- spectrophotometric method comparing with McFarland standard solution.

Dear All,

I want to prepare 2×10^10 cfu/ml but the highest Macfarland std is 3×10^9 and I really have no time and staff for plate culturing. What should I do?

Dear , you can find useful information in link below:

technologyinscience.blogspot.com/2011/11/cfu-colony-forming-unit-calculation.html

I want calculate CFU/g of Green tea extract. I taken 1g sample dissolved in 9ml saline solution and 0.1 ml is plated onto Plate Count Agar from the dilution. After incubation, 10 colonies are counted on the plate. Calculate CFU/mL of the original Sample?

The volume of the saline will have been increased somewhat by the addition of 1 g of material, but we will ignore that for now. Taking the original sample volume to be 9 ml, you plate 0.1 ml, which is 1/90 of the sample and got 10 colonies. (Ideally, you would make this measurement in triplicate and take the average.) Multiply by 90 to get the number of colonies in the original sample, which is 900. Divide by the sample volume in ml to get CFU/ml = 100. Alternatively, if you want CFU/g, divide the CFU in the whole sample (900) by the grams of extract dissolved (1) to get 900 CFU/g.

My fellow researchers, how can i convert colony forming unit per gram cell (CFU/g) to gram per liter cell (g/l) or kilogram per liter cell (kg/l)

Un estandar de McFarland ?

Dear Ozge Uysal,

Dear,

theoretically, the growth of a bacterial cell gives a single colony.

so, we can according to this logic,

inoculate any bacterial sample to know the number of initial cells.

Doing repetitions with different dilutions is essential.

I agree with Dr. Adam's response.

Make a suspension of the thawed glycerol suspension in saline. Now rotate this in full speed on a vortex mixture to break all clumps. Plate it out on a suitable agar medium. Incubate the plates appropriately and the count the colonies which is the required number of CFU.

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

No dilution may be required of the original glycerol suspension as the viability in the frozen culture will be low.

Dear

Ozge Uysal

see attached file there is formula , you can used to find CFU

I agree too..with Dr. Adam's response.

Dear Ozge,

We have calculated CFU (colony forming unit) in case of yeasts as well as bacteria. Colony-forming unit (CFU or cfu) is a measure to know viable bacterial or fungal cells in a given sample. Miles and Misra technique is employed to calculate CFU. It can be done in liquid ( colony forming units per ml) and solids ( colony forming unit per gram).

The following formula is used to calculate CFU.

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

Wish you best of luck in your scientific career.

Prof.Dr.Mahendra Pal

Founder Director of Narayan Consultancy on VPH and Microbiology

I agree with Dr. Adam's response

this is can be done by special equation

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

The following formula is used to calculate CFU.

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

Dr. Ozge Uysal

By looking at above Answers if the query yet remained.........?

• For antibacterial activity if you are trying to know about the CFU or number of bacteria against which you will try to know antibacterial potential of your material. Simply you can take the absorbance of fresh culture using spectrophotometer ( Absorbance @ 600nm 0.063 ) or match your culture with McFarland turbidity standard having approx. cell density (1X10^8 CFU/mL).

Simply,

CFU/ml = (no. of colonies x dilution factor) / volume of culture plate(ml)

You can calculate the cfu/ml for bacteria by making some dilutions and taking the last dilution, then you must use hemocytometer to calculate the colonies number, then you must apply the following equation:

cfu/ml= (Colonies number x dilution factor) / Volume of culter plate

With regards.

Real Time PCR,

Standard Curve,....

Hi

CFU/ml = (no. of colonies x dilution factor) / volume of culture plate(ml)

Diluting Samples, Plating and Incubation

If you simply smear a microbe sample on an agar plate, you'll see so many colony-forming units that the individual colonies will blend together, making them impossible to count. To solve this problem, mix the sample into a liquid medium, take a small amount of that mixture and further dilute it. Repeat this process 6 to 10 times. Spread the final dilution on an agar plate and incubate it for four to seven days before you count the colonies.

Calculate the number of bacteria (CFU) per mL or gram of sample by dividing the number of colonies by the dilution factor The number of colonies per mL reported should reflect the precision of the method and should not include more than two significant figures.

The CFU/ml can be calculated using the formula:

CFU/mL = (no. of colonies x dilution factor) / volume of culture plate

For example, suppose the plate of the 10^6 dilution yielded a count of 130 colonies. Then, the number of bacteria in 1 ml of the original sample can be calculated as follows:

Bacteria/ml = (130) x (10^6) = 1.3 × 10^8 or 130,000,000.

CFU/mL Practice Problems - CFU/mL Calculation Examples

Problem 1:

Five ml of Bacterial Culture is added to 45 ml of sterile diluent. From this suspension, two serial, 1/100 dilutions are made, and 0.1 ml is plated onto Plate Count Agar from the last dilution. After incubation, 137 colonies are counted on the plate. Calculate CFU/mL of the original Sample?

Answer:

First thing we need to know is the Dilution Factor, or how much the original sample is diluted:

Here Initially 5mL in 45mL = Final Volume / Sample volume = 50/5 = 10.

Then two serial dilutions of 1/100.

Total Dilution Factor = 10 * 100 *100 = 10^5

CFU/mL = cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

= (137 * 10^5)/0.1

=1.37*10^8

So Total colony forming units = 1.37*10^8 CFU/mL

Converting CFU/mL to Log value

For example,

Total colony forming units = 1.37*10^8 CFU/mL and you want to convert it into Log value,

Just take Log (CFU/mL)

Here, log (1.37*10^8) = 8.13924922.

We have calculated CFU (colony forming unit) in case of bacteria and yeasts. Colony-forming unit (CFU or cfu) is a measure to know viable bacterial or fungal cells in a given sample. Miles and Misra technique is employed to calculate CFU. It can be performed in liquid ( colony forming units per ml) and solids ( colony forming unit per gram).

The following formula is used to calculate CFU.

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

You may refer laboratory handbook, "Collins and Lyne's Microbiological Methods" .

Thanks a lot all for valuable suggestions and guidelines.

CFU/ml = (no. of colonies x dilution factor) / volume of culture plate

CFU/ml = (no. of colonies x dilution factor) / volume of culture plate

Dear Ozge

CFU stands for Colony Forming Units, a microbiology term used to quantify how many bacteria exist in a solution. Depending on the concentration of your sample, you need to perform multiple dilutions and plate the different samples onto petri dishes. If you have too many bacterial colonies, they are hard to count, and if there are too few, the sample may not be representative. It is generally a good idea to plate the original solution, then a 1/10 dilution (1 part solution, 9 parts saline), a 1/100 dilution and possibly a 1/1000 dilution.

Perform a preliminary count of each dish once the bacteria incubates, which usually takes one or two days. Count only individual colonies, which should be distinct, isolated dots, not a whole blob of different colonies grown together. Choose the plate which has more than 30 of these colonies but less than 300.

Count the number of individual colonies. This is the CFU number of your dilution -- you will have to perform a simple calculation to determine the CFU of the original sample. For this example, use a hypothetical plate containing 46 colonies.

Determine the size of the dilution you used. (Ideally, you labeled the petri dishes ahead of time.) For this example, mix 1 mL of bacterial culture with 99 mL of saline. This is a 1/100 dilution.

Multiply the degree of the dilution by the amount you actually plated. If you plated 0.1 mL of your 1/100 dilution onto the agar, you multiply 0.1 x 1/100, for a result of 1/1000 or 0.001.

Divide the CFU of the dilution (the number of colonies you counted) by the result from step 4. For this example, you work out 46 ÷ 1/1000, which is the same as 46 x 1,000. The result is 46,000 CFU in the original sample.

Hello

Kindly look at links here

Article A method for high throughput determination of viable bacteri...

https://orbitbiotech.com/how-to-calculate-cfu-colony-forming-unit-cfu-colony-forming-unit-cfu-ml-cfu-g-cell-count-microbial-counting/

Good Luck

Fruitful discussions.

Use the Miles and Misra technique where CFU/ml= No. of colonies*dilution factor/Volume of inoculum (volume of sample plate)

I have a problem, because if I can count the number of bacteria in the unit CFU/ ml, I would like to know how to convert this amount to the unit gram per liter?

HELLO Joanna Chojniak-Gronek

it's simple, if you will have the number/mL you can then calculate the number/Liter... cependant, ce nombre ne peut pas être converti en grammes car il s'agit de bactéries.

Thank You for answer. I know how calculate number of bacteria/ml to number of bacteria/L. But in some materials I found unit gram per liter, so I don't know how caltulate or convert to those unit.

I just want to know the protocol, how we can separate the sample from the Inoculant after one or two weeks of formulation to check CFU value and then how we can calculate CFU value?

The CFU/ml can be calculated using the formula:

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

https://youtu.be/jdnOjoOO6qY

www.aphis.usda.gov › vet_biologics › publications › BBSOP0019

CFU= (No. of colonies* Dilution factor)/volume of inoculum used for plating

Use the formula:

[Number of colonies counted] × 10 × [how many times the sample must be multiplied to get to the original concentration: for example, 105] = Number of colony forming units (CFU) per milliliter of starting culture. This is the bacterial growth in your petri dishes.

Considering above literature and with the help of digital collony counter unit, it is very easy to measure.

https://www.youtube.com/watch?v=jdnOjoOO6qY

Miles and Misra technique is employed to calculate CFU

You can use the following formula to calculate colony forming unit (CFU)

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate

CFU per ml=Average number of colonies for a dilution×50×dilution factor (Miles and Misra)

You first make a 10 fold serial dilution. select the plates between ( 30 - 300 cfu) as reported by Miles and Misra technique is employed to calculate CFU

You can use the following formula to calculate colony forming unit (CFU)

cfu/ml = (no. of colonies x dilution factor) / volume of culture plat.

CFU/ml = (Number of colonies × dilution factor)/ Volume of culture plated

Cfu/ml=(no of colonies × dilution factor)/(volumeof culture plate)

You can calculate the CFU, suppose you have a plate of the 10^6 dilution that yielded a count of 130 colonies. Then, the number of bacteria in 1 ml of the original sample can be calculated as follows: Bacteria/ml = (130) x (10^6) = 1.3 × 10^8 or 130,000,000.

ok

So I saw an article referencing log 7 to log 8 CFU/mL of bacteria in a wound biofilm. Do I interpret this to mean that in this study there were 10^7 to 10^8 bacteria per mL^3?

Wade Farrow that is the correct interpretation, except that your units are off. Did you perhaps mean cm^3? Another common practice is to report change in bacterial number on a log scale. For instance, if the biofilm started with 10^8 CFU/mL and reduced to 10^7 CFU/mL after a treatment was applied, a log 1 reduction has occurred. Also, remember that CFU is not quite the same thing as bacteria; it is just a proxy measurement. This is especially important to keep in mind when comparing results reported as CFU and those reported as Most Probable Number (MPN).

is it possible to calculate it by machine???

Hi,

You can check the below link for cfu/ml calculation :

https://youtu.be/Z7qXfqlmF0M

Hope this helps.

Hope this helps.

CFU/ ml is calculated after serial dilution and incubation of the culture plates using the formula:

Average colony count x dilution factor/ volume of inoculum plated

manual work depends on experience , which is varied from one to another

I agree with previous answers

https://www.youtube.com/watch?v=jdnOjoOO6qY

Counting CFU requires the following -

Dilution factor of sample you are using to isolate the particular bacterial or fungal species.

The volume used for the isolation (Inoculum volume)

CFU/ml is calculated by formula

no of colonies x dilution factor

-------------------------------------------------

inoculum volume

First count the no of colony observed after required time period of growth for that microorganism, manually or by colony counter then calculate the CFU/ml by above formula.

Good discussion

CFU can be calculated as:

CFU/mL= Number of colonies X reciprocal of the dilution factor

E.g. Suppose the dilution was made from 10-1 – 10-5 and from these dilution 1ml of aliquots were spread on appropriate media. After incubation time you may count the number of colonies as 417 from 10-1, 363 from10-2, 150 from 10-3, and 8 from 10-4

The CFU is 150 X 103 = 1.5 X 105 CFU/mL

N. B. The number of colonies should be between 30-300

i dont know

its better to depend of well calibrated instrument , to speed work and quality of the work

CFU= no .of colonies X dilution factor /volume of culture plate

You can use the following text as a guideline for calculating cfu...."Plating techniques are simple, sensitive, and widely used for

viable counts of bacteria and other microorganisms in samples of

food, water, and soil. Several problems, however, can lead to

inaccurate counts. Low counts will result if clumps of cells are

not broken up and the microorganisms well dispersed. Because it

is not possible to be certain that each colony arose from an individual

cell, the results are often expressed in terms of colony

forming units (CFU) rather than the number of microorganisms.

The samples should yield between 30 and 300 colonies for most

accurate counting (counts of 25 to 250 are used in some applications).

Of course the counts will also be low if the medium

employed cannot support growth of all the viable microorganisms

present. The hot agar used in the pour-plate technique may

injure or kill sensitive cells; thus spread plates sometimes give

higher counts than pour plate".................... For detail you can read Microbiology by Presscott

CFu/ml is equal to (the number of colonies counted * the dilution factor)/ volume of inoculum. one has to make sure the colony counted should be in the range of 30 and 300. That is the only colonies counted that is appropriate for calculating the CFu

Dear Ozge Uysal

I think the answers here are very informative and valuable. Cheers!

CFU/mL= Number of colonies X r the dilution factor/Volume plated

Suppose you got 300 colonies at 10-6 dilution point and poured 0.1 ml

then calculate it as 300x10^6/0.1=3x10^9 CFU/ml

Very insightful answers on calculating colony forming unit of a microbial cell.

Enumeration of bacteria as CFU

For example, 1 ml of probiotic culture solution was diluted 7 times in peptone water using 9 ml of peptone water.

Therefore, the dilution factor = Final Volume/Sample volume × diluted concentration

=10/1 × 107 or 10 × 107

Then 1 ml of diluted probiotic solution was inoculated and cultured for 24 hours at 37˚C. The colony counted for each plate was 88.

CFU/ml = (no. of colonies x dilution factor)/volume inoculated on culture plate

= (88 x 10 × 107) /1

= 8.8× 109 CFU/ml

= 9.94 log CFU

It is better to cultivate frozen bacteria and use fresh over night bacteria for testing?

answers are here very informative and easy to understand..thank you every one.