I am analyzing a treatment on fungal spores to observe the killing effect of the treatment on the pathogen. For the treatment I spread 1 million fungal spores on media plate, treat the plates for different time duration, collect the spores from the media, perform serial dilution and then plate out. I want to compare the effect of treatment at different time points. I often get 1/2 colonies or sometimes 0 after 3 min of treatment without any dilution. I plate then in triplicate and sometimes I get 0 in one, 1 in 2nd and 2/3 in the third one. If I take average it becomes around 1.5. How should I express that while presenting the data? Should i just write it as 0 and assume 100% are killed?
A colony forming unit (CFU) is a unit used to estimate the number of viable bacteria or fungal cells in a sample. Concentrations of colony forming units can be expressed using logarithmic notation, where the value shown is the base 10 logarithm of the concentration. Counting colonies is traditionally performed manually using a pen and click-connter. Alternately semi-automatic (software) and automatic (hardware+software) solutions can be used. The software used to count colonies are OpenCFU, NICE, ImageJ and Cell Profiler. Instead of colony forming unit ,the parameters Most Probable Number (MPN) and Modified Fishman Units (MFU) can be used to used to count the microbial cells. Therefore, I suggest to count the number accurately using any of the method and dont assume 100% is killed.
Thanks for your answer. But what about limit of detection (LOD). Shouldn't I have a LOD?
In MPN method you may count from 10 spores to hundred thousand spores depend on dilution factor. By using software you may count a single spore also.
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Hello Tahria Najnin
Several useful references on attachment 1
https://technologyinscience.blogspot.com/2011/11/cfu-colony-forming-unit-calculation.html
2
https://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1959.tb01482.x/pdf
3
https://biology.mit.edu/sites/default/files/hemacytometer%20activity%20revised%207-23-13.pdf
5
https://www.dummies.com/education/science/biology/how-to-count-the-number-of-cells/
6
http://www.sas.upenn.edu/LabManuals/biol275/Table_of_Contents_files/14-Enumeration.pdf
11
https://ocw.ehu.eus/file.php/253/Temas/2_BASIC_METHODS_FOR_THE_ENUMERATION_OF_MICROORGANISMS.pdf
i
http://faculty.weber.edu/coberg/class/3853/3853%20Microbial%20Testing%20Procedures.htm
l
https://www4.ncsu.edu/~lagillen/SSC%20532/Chapter%2010/Chapter%2010.html
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