Independent Evaluation of Prepared Gamma Irradiated Dehydrated Culture Media to Traditional Bulk Dehydrated Culture Media from Various Manufacturers

Introduction:  Microorganisms require nutrients, energy source and certain environmental conditions in order to grow. Due to the diversity of microorganisms, there are numerous types of media required for growth. Prior to use, media often requires a sterilization step, e.g. autoclave sterilization; however, autoclave sterilization can lead to the breakdown of certain carbohydrates. A new technique employing gamma irradiation has been adopted as a viable alternative that uses water soluble polyvinyl alcohol (PVA) film pouches (inert in solution) fabricated to hold the dehydrated media eliminating the need for autoclave sterilization.

Purpose:  Evaluation of growth parameters (appearance, growth promotion, sterility and pH) in order to compare commercially available dehydrated media and one ready-to-use PVA media.

Methods:  Nine different types of media, including bulk dehydrated culture media from two manufacturers and the alternative PVA media pouches were evaluated. Three separate batches of each media were prepared and evaluated in triplicate. For growth promotion, replicates were inoculated with 10 to 100 CFU and growth turbidity scored using McFarland Standards using a scale from zero to four. The total scores were tabulated and averaged for each media tested.

Results:  PVA media performed as well as the autoclaved media prepared from commercial dehydrated media for all nine formulations evaluated. The PVA media produced a total score of 138, with a 2.56 average per replicate. The two traditionally made medias produced total scores of 132 and 121 with average scores of 2.44 and 2.24, respectively.

Significance: The data generated within the evaluation indicated that the PVA media performed equivalent to current commercially available bulk dehydrated media and can provide the end user a high level of quality assurance and quicker time to results by eliminating the need for traditional media preparation steps.