Microbial challenge/product sterility test

Aerosol Challenge. At the risk of oversimplifying the procedural demands of microbial testing, here is a summary of how a microbial challenge/product sterility test is performed. There are two types of whole-package microbial barrier tests currently in use. 

All finished products are tested for sterility in a controlled-access clean room environment in a laminar flow hood, which provides no greater level of a microbial challenge than that encountered in the fill environment. The testing environment consists of a gowning room and sterility test suite that meets the same air quality standards as the hlling suite. 

A sterile product incorporated a preservative system to cover withdrawal of a multidose liquid product. The product passed the USP XX microbial challenge test when first made and packed. After six months it was noticed that the level of ethylenediamine tetra acetate (EDTA) had significantly reduced, possibly by chelation with heavy metals + surface adsorption onto the plastic. A repeat microbial challenge test was not passed. It was theorised that this was due to slight preservative loss coupled to the loss of EDTA which tended to enhance the preservative efficacy, i.e. a chemical + physical change (preservative adsorption) had created a drop in preservative efficacy. Changing the EDTA/preservative levels was subsequently necessary in order to meet the microbial challenge test over the full shelf-life period. 

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