What is PRAS Media?

The superior recovery of anaerobes on PRAS media is a direct consequence of its oxygen-free manufacturing. Unlike conventional media, which are prepared in the presence of atmospheric oxygen, PRAS media is produced and sterilized under strictly anaerobic conditions. This prevents the formation of oxidized compounds, like peroxides, that are toxic to many fastidious anaerobes.

• A 1970 study by McMinn and Crawford found that prereduced anaerobically sterilized media recovered more than twice the number of anaerobic bacteria from clinical specimens compared to conventional methods. Many of the isolates recovered only on PRAS media would not grow when placed in fluid thioglycolate medium. (McMinn, M. T., & Crawford, J. J. (1970). Recovery of anaerobic microorganisms from clinical specimens in prereduced media versus recovery by routine clinical laboratory methods. Applied Microbiology, 20(4), 435–441.)

The core of Oxyrase’s technology is its patented oxygen-free preparation, which is what makes their media a true PRAS product. Our process uses the Oxyrase® Enzyme System to actively remove dissolved oxygen from the media before and during sterilization. This not only creates a reduced environment but also prevents the formation of inhibitory oxidized compounds.

• The technology’s foundation comes from the work of Dr. Howard Adler and his colleagues at Oak Ridge National Laboratory, who found that cell-membrane fractions from Escherichia coli and related microorganisms could effectively reduce oxygen to water. This discovery led to the development of the Oxyrase Enzyme System. (Oxyrase, Inc. (1996). The Use of Microbial Membranes to Achieve Anaerobiosis: The Oxyrase® Enzyme System. Publication dated September 4, 1996.)

While many anaerobic culturing systems require added labor and bulky equipment, Oxyrase products are designed to streamline the workflow. Our products eliminate the post-reduction process. Further evidence for this is the OxyPlate™, which acts as a self-contained anaerobic chamber, allowing for individual plate handling and standard incubator use.

• A study published in the Journal of Clinical Microbiology evaluated the Oxyrase OxyPlate system’s ability to support the growth of clinically significant anaerobes compared to a conventional anaerobe chamber. The study concluded that the OxyPlate system was effective in creating an anaerobic atmosphere and supporting bacterial growth, making it a “useful addition to the clinical microbiology laboratory lacking resources for traditional anaerobic culturing techniques.” (Wiggs, L. S., et al. (1998). Evaluation of the Oxyrase OxyPlate Anaerobe Incubation System. Journal of Clinical Microbiology, 36(6), 1664–1667.)

The long shelf life of Oxyrase media is a direct benefit of the Oxyrase® Enzyme System’s continuous oxygen-scavenging activity. The media is packaged in oxygen-impermeable film, and the enzyme system maintains the reduced state of the medium.

The Clinical Microbiology Procedures Handbook (2016) recommends PRAS media as the optimal choice for anaerobic bacteria growth (Wiley Online Library).

The cost-effectiveness of Oxyrase PRAS media is based on its ability to lower overall lab expenses despite a potentially higher per-plate price. The evidence points to savings on labor, equipment, and consumables.

• The elimination of anaerobic chambers, jars, and bags directly reduces equipment and maintenance costs.

• The improved recovery rates mean fewer negative or inconclusive results, reducing the need for repeat testing and the associated costs of labor and materials.

• The extended shelf life minimizes product waste from expired media, which is a common issue with conventional plates.