Product Neutralization for Rapid Microbiological Test Methods

Q. We have developed an in-house broth to neutralize a preservative for traditional microbiological testing following USP <61> Microbiological Examination of Non-Sterile Products: Microbial Enumeration Tests.  We would like to use a rapid-test method to release product faster, but is there a broth that will be effective on our products?

A. Choosing the right rapid-test method is important.  Some rapid-test method manufacturers require use of their proprietary broth while other systems are more flexible.  Flexible rapid-test method systems allow users to closely follow their validated, traditional method, including the type of media and incubation temperature used.  Flexible systems allow users to incorporate additional neutralizing agents or use broths developed in-house.

Trypticase Soy (Soybean-Casein) and Letheen are typical broth options for testing many pharmaceutical products. For products that are particularly difficult to neutralize, Trypticase Azolectin Tween (TAT) broth is commonly selected as an enrichment medium. TAT broth is low in ATP, supports the growth of a wide range of micro-organisms, and contains the neutralizing agents polysorbate 20 and lecithin.  

Single broth enrichments, with and without added neutralizing agents and at appropriate product concentrations, have been validated using rapid-test methods for effective microbial-limits testing across a wide range of products. If you have successfully validated your product using the traditional, growth-based method, adopting a flexible, growth-based rapid method that allows the use of your validated, in-house broth is highly likely to be successful.

With the availability of flexible systems capable of using a variety of broths, concerns about product neutralization should not prevent microbiologists from looking seriously at rapid microbiological methods.

—Lori Daane, PhD, vice-president for scientific affairs at Celsis.

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