I am currently trying to quantify the viable count of trichoderma spp. in a compost sample. However I do not have much literature on the range for plate count of fungi. should I be following the standard 25-250 colony range for APC or should I follow the the 10-150 colony range as recommended by the american FDA for yeast and mold? thank you so much for answering.
Plate count for mycelial fungi in your context is pretty meaningless. You can't separate individual cells of mycelium so hundreds of actively-growing cells may compose a single colony. Conversely, dormant condia liberated by culture may offer great numbers of colonies. Even more of a problem would be chasing the count of one fungal genus.
Please do not consider FDA's methods for foods/drugs/cosmetics as useful for the study of compost. The limits to which you refer are practical in estimating numbers. Counts beyond the specified numbers are not consdiered accurate due to the the size of fungal colonies on typical agar plates,
I have found the 10 to 150 range better; above 150 there is the risk of confluent growth.
@ Dwight, my experience is 30 to 100 range is better for fungi. Above 100 colonies is very difficult to count for fungi and less than 30 colonies is too small a sample size to present an accurate representation of the original sample.
About 50-100 colonies in one plate, this number can be counted, but if the number of colonies increased more than this number, it can not be counted easily.
I agree with Geis. For fungi, plate count is valid if you are using spores but if you are using filamentous mycelia, I don't think it is valid. Even if you plate the fungi, one colony can originate from one or multiple mycelia cells, it is not an accurate method to quantify fungi.
Plus, the compost sample may consist of numerous fungi other than Trichoderma. How can you be sure which colony is Trichoderma and which is not? Even if you are using Trichoderma selective medium, it does not guarantee that other fungi won't be able to grow on that media. If you plate the compost, the only thing that you can confirm is the presence or absence of Trichoderma.
Is there a reason why you need to do plate count for Trichoderma in the compost? If you wan to see the ability of Trichoderma to degrade organic matter, you can just do further tests on the compost and compare between sample with Trichoderma and sample without Trichoderma.
Hope this helps.
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