I have this specific query that I am trying to get answered.

USP sterility testing by membrane filtration validation has as its key step a bacteriostasis/fungistasis test. This test is required to validate that the "product" being tested has no "inhibitory substance" which might give a false negative.

So far so good.

The USP validation step details how this is to be done. First the product is "filtered" through the membrane filter. Then it is "RINSED" with 200ml of peptone buffer. Approximately 10-100 cfu of bacteria or fungus is added to 100ml of peptone buffer and again passed through the membrane filter. Finally, the growth medium is added to the cannister and the cannister is incubated.

My questions are as follows:
1. Rinsing the filter membrane with 200ml of peptone buffer for many products will leave no detectable residue of the product on the membrane. I have tested this with my product and we detected NO product on the membrane after the 200ml rinsing process.
I suspect this is true of a number of highly soluble substances.
What I am saying is that there is no detectable interaction between the product and microbe in this validation process. So how does this USP validation process help me establish that my product has no inhibitory effect on microorganism's growth.

It seems that a more sensible approach would be to skip the rinse and add growth medium with 10-100 cfu of microbes to the cannister and evaluate the growth.

So; does anyone agree? does my thought process make sense? has anyone else encountered this ? any thoughts would be very welcome.

I have this specific query that I am trying to get answered.

USP sterility testing by membrane filtration validation has as its key step a bacteriostasis/fungistasis test. This test is required to validate that the "product" being tested has no "inhibitory substance" which might give a false negative.

So far so good.

The USP validation step details how this is to be done. First the product is "filtered" through the membrane filter. Then it is "RINSED" with 200ml of peptone buffer. Approximately 10-100 cfu of bacteria or fungus is added to 100ml of peptone buffer and again passed through the membrane filter. Finally, the growth medium is added to the cannister and the cannister is incubated.

My questions are as follows:
1. Rinsing the filter membrane with 200ml of peptone buffer for many products will leave no detectable residue of the product on the membrane. I have tested this with my product and we detected NO product on the membrane after the 200ml rinsing process.
I suspect this is true of a number of highly soluble substances.
What I am saying is that there is no detectable interaction between the product and microbe in this validation process. So how does this USP validation process help me establish that my product has no inhibitory effect on microorganism's growth.

It seems that a more sensible approach would be to skip the rinse and add growth medium with 10-100 cfu of microbes to the cannister and evaluate the growth.

So; does anyone agree? does my thought process make sense? has anyone else encountered this ? any thoughts would be very welcome.

These tests are pasrt of the "Validation ofNeutralization methods - Recovery Comparison" under USP <1227>

When you filter the antimicrobial agent through the membrane filter, it passes through and all the residual antimicrobail agents those get adhered to the filter paper are also washed by the subsequent peptone rinses. Now, when you add your challenged microrganisms, they should be able to give recovery (as per USP criteria) and if they are not, it means the antimicrobial agents are not getting rinsed and still remain on filter paper.

Thus the method is not validated and doesnot meet the neutralizer efficacy and neutralizer toxicity.

Ajit,
actually my question is a little complicated.

My product is neither antimicrobial nor has preservative in it. What I was asking is as follows:
1. Is it acceptable to structure a validation protocol which actually tests the BF properties of my product if any. This can be done easily if we simply skip the rinse part of the test in this protocol.
Successful recovery percentage would then establish that the product itself has no BF properties.

The logic behind this is that it will allow us to skip the "recommended" revalidation which lists as one of its reasons "several microbes develop resistance to antimicrobial and preservative components of products". If during the validation we can prove that our product is neither an antimicrobial nor has preservative in it and has no BF tendencies; we can effectively make a case that the validation is life cycle barring any changes in product or production processes.