In routine, I need those inoculum with a small number (NMT 100 CFU) to conduct growth promotion test. However, the inoculum preparation has not been validated so I need some references to perform this validation. Currently, I am preparing the inoculum by take a loop full of single colony (not more than 5 passage) to 10 mL of saline solution, then perform serial dilution. Each diluted solution is enumerated and incubate (bacteria at 30 - 35 deg C for NMT 3 days and yeast mold at 20 - 25 deg C at NMT 5 days). Along the incubation period, I store the diluted suspensions at 2 - 8 deg C. Then, I will use the diluted suspension right after incubation period and colonies observation. From this method however, seem like I don't use a fresh inoculum. Can anyone suggest the proper method to prepare inoculum to obtain 100 CFU? thank you in advanced.
I have no idea why you would incubate saline suspensions after dilution. There are some relevant publications - https://www.pda.org/pda-letter-portal/archives/full-article/growth-promotion-testing-for-em
Microbiologics , bioMerieux and others sell certified devices that establish ~100 cfu. It is not cost effective to do it yourself.
https://www.biomerieux-usa.com/industry/bioball
https://www.microbiologics.com/item-type/Product/product-format/EZ-Accu-Shot
Hi Phil Geis , As previously explained, I enumerate each diluted suspension by plate count method then incubate the plates (bacteria at 30 -35 deg C and yeast mold at 20 - 25), it aims to know which dilution level that contains inoculum at NMT 100 CFU. During incubation period of enumeration test, I store the diluted suspension at 2 - 8 deg C. I would prefer to say "storing" than "incubating" actually. At this point, I should not keep the diluted suspension at 2-8 deg C until I use it, but it seems difficult to prepare it freshly.
Thank you for your answer & references.
Thanks. The statement offered did not make that clear.
Please seriously consider the devices. Using valuable highly -skilled folks to perform this laborious routine function is not cost effective. Gather they're in the risk assessment business - not the device making business.
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