I made the agar plate spread directly with the crude extract instead of doing serial dilution. So how can I calculate CFU from the agar plate? Or it can only be calculated from the serially diluted plate?
You can do the calculations from the crude extract, but if you have results from next dilutions, take these results in consideration too.
You can see ISO 7218 for guidance
Depending on the crude extract, you can have growth inhibitors that might affect bacterial recivery
If you know the volume and bacterial count in the original inoculum, then you can simply count the colonies. If you got more than 300 colonies, then you're recommended to do serial dilution of your bacterial suspension to avoid such crowded and overlapping colonies.
Thank you so much @Jameel M. Abduljalil. the volume I took is 0.1 ml and I got around 40+ colonies. So what is the formula should I use for calculating CFU/mL? or can I count the colonies directly instead of putting calculations?
You have to take into account the quantity of sample from you get the extract, as well as the quantity of solvent.
For instance, let’s say that you have 5 g of sample and 20 mL of solvent. After the extraction, each mL of extract corresponds to (5/20) 0.25 g of sample, and 0.1 mL of the crude extract in the plate corresponds to 0.025 g of sample.
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