I'm trying to figure out the methodology according to the American Pharmacopeia to use in non-sterile cosmetic assays.
If I dilute 10g of my sample with a neutralizing broth, letheen in this case, do I need to follow up with a pre-inoculation of 10mL of this dilution into another 90mL of TSB?
It seems redundant to me, since letheen is already a growth promoting broth. I'd just follow through with incubation and use the original dilution as my sample.
Any help is welcome, I've been breaking my head over this and can't seem to find an answer.
In USP 61's suitability of the counting method, there's a section regarding neutralizing agents. Since the product I'll be testing has antimicrobial activity, I have been suggested and recommended the use of Letheen broth to inactivate QACs and other substances. That's where my doubt stems from.
Your product includes quat actives?
Can you neutralize, demonstrate suitability? per 61's TSB- then forgot Letheen. If TSB does not work, try Modified Letheen (per US FDA*) and do not bother with TSB.
* https://www.fda.gov/food/laboratory-methods-food/bam-chapter-23-methods-cosmetics
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