What is the Difference Between "Pre-Reduction" and "Post-Reduction" of PRAS plates?

July 21, 2016

What is the Difference Between

What is the difference between pre-reduction and post-reduction of plated anaerobe media?


The 'Pre' in pre-reduction refers to that time before the plate is made. Reduction is done at this step to prevent oxidized products, that are harmful to anaerobes, from being formed during sterilization (autoclaving) of the medium. Harmful oxidized products formed at this stage of media make-up cannot be removed later.

The 'Post' in post-reduction refers to that time after the plate is made. Reduction is done at this step to prepare the plate for use, i.e. inoculation with anaerobes. This is done to provide an optimal environment for the anaerobic, bacteria to initiate growth.

To make 'PRAS' medium (pre-reduced, anaerobically sterilized) requires the pre-reduction step.

Some media 'made for anaerobes' only get the post-reduction treatment. A convenient way to visualize the recalcitrance of oxidized products to subsequent alteration is to imagine a rusty nail being put into an anaerobic environment... it does not reduce (remove/reverse) the rust... anymore than putting an oxidized plate, made without pre-reduction, into an anaerobic environment to convert it to a 'PRAS' plate.

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