i work on powder infant food , i take 1g then i put it in 70ml liquid media in flask and incubate it for 24h , then i take 1ml and diluted it three times in 9ml of water after that i take 0.2ml from tube 2 (1:100) then i spread it on solid media in petri dish , incubate for 24h and the count of colonies was 80, i calculate cfu and the result 80×100 CFU/ml is that correct? i need cfu/g because the orginal sample powder food? Can you help me?
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 in following link
http://technologyinscience.blogspot.com.eg/2011/11/cfu-colony-forming-unit-calculation.html#.WSHf_W4lHIU
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.
take a gm and add 10ml.....let it mix....take a ml and do cfu in petroff hausser chamber
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