Expert view: Sterility testing of challenging samples
While membrane filtration is often straightforward, some sample types can be challenging. These include difficult-to-filter viscous oils, water-in-oil emulsions and fatty base ointments as well as samples containing substances that inhibit microbial growth.
High‑density cell cultures can also prove problematic. However, membrane filtration can be made to work for most products perfectly well.
Pharmacopeia standards, such as USP <71> and EP <2.6.1>, recommend membrane filtration as the preferred method for sterility testing whenever the nature of the product permits. Filtration methods have the advantage of allowing large sample volumes to be tested for meeting standards requirements and recommendations. Also, for products with antimicrobial activity, filtration allows rinsing and thus the removal of the inhibitory characteristics of the product.