It is better to test the media not only for the compendial microorganisms but also for those specific microorganisms which have been recovered from past tests (e.g. a Sterility Test contaminant or a frequent environmental monitoring isolate). (For reference Pl. see FDA Guidelines on sterile drug produced by aseptic processing, PIC/S on sterile testing and USP chapter <71> and <1116>). You can also justify with the following statements
a.Can You say that the new batch of media is as good as a previously qualified batch? This question cannot be answered adequately except by statistical comparison, given the variability of microbio-logical data. So the best solution is to test the media.
b. There is no such media which could be non selective.All the media are selective although the level of selectivity is different.Therefore it is better to test the selectivity of media specially for the microorganism isolated from environment and as sterility test contaminants to avoid any false negative results.