Culture Media Training Academy: Correct Dissolution of Dehydrated Culture Media

September 12, 2019

Ensuring that your media is dissolved fully before heating removes the risk of seeing un-dissolved media or burnt particles in your agar, which could easily be mistaken for microorganisms.  Help prevent problems in your lab with the correct dissolution of media.

Video Transcript

A problem that can occur with agar plates is the presence of black or dark particles that are caused by burning culture medium.

Here is a xylose lysine deoxycholate agar or XLD for the detection of Salmonella.

If prepared correctly, the agar is a clear red gel.

You can see here that there are black particles throughout the agar. This is especially a problem for this agar as the target organism, Salmonella, grow as black colonies on the agar, thus burnt particles could be misinterpreted for a pathogen.

This is an extreme level of burning and users may normally only see only a couple of charred particles.

One way this can occur is the improper dissolution of powder.

Here I have added the powder to the water. As you can see, it sits on top of the water before slowly dissolving.

If heat is applied now, before all powder is dissolved, parts of the powder may burn and form the precipitate you saw earlier.

To prevent this from happening, powder should be fully solubilized before heating.

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Category: Solution Spotlights