On 18 Mar 2002 16:09:56 -0000, kliska at novocol.com (Kim Liska) wrote:
>>I am looking for a bioburden test for creams/lotions. How do you dissolve a
>white cream into a clear liquid and what bioburden technique would be better
>to use (MPN, plate count, etc.) for this material? Thank you.
1) Creams and lotions should be self-preserving. That is, they
should pass a preservative efficacy test. If you perform a count and
then re-count after four hours, any pathogenic bacterium should have
had a 90% reduction in count. This is a 4 hour D-value.
Non-pathogens should have a 28 hour D-value. In my opinion, the
standard USP efficacy test is too qualitative and leaves room for
bacterial adaptation, because its "so-called acceptable" D-values are
far too long.
2) Now, as to the method, you need to perform a "Preparatory" test,
as outlined in the USP. This tests validates the enumeration method,
esp. because of preservative carry-over problems. Generally, for QC
that I use is a sterility test with a liquid preservative neutralizing
broth and pre-incubation and then a streak of the liquid on
neutralizing agar. I do not use counts, since the creams and lotions
should be sterile if the preservative is working.
3) For times when a count *is* really needed, I use the USP
Preparatory test and then the USP preservative neutralizing plate
count method. That is the only legal method I know of.