Well that depends on what you are trying to grow on them. For legionella we use Buffered Charcoal yeast extract which is basically black due to the presence of activated charcoal. However, as I said before this needs to be assessed for what you are trying to grow as the charcoal might inhibit it. Of course if you are only after the color you can add filter sterilized food dye to the media but again you have to test whether it causes inhibition of your bacteria.

Thank you Hanna Alalam ,

Actually I'm working with agar to investigate to chemotaxis of nematodes in interaction with root exudates. I'm looking for a black dye without organic materials, which may intervene in the chemotaxis of the nematode.

I already tried with activated charcoal. However, charcoals residues on the agar plate disrupt the image capture (my goal is to take pictures of the plate and then identify nematodes trackings on my computer). Optimally, the coloured agar should be purified (no tracks of residues).

Hi Simon Dingsdag

Thank you for your advices !

Last time I stained the agar with acid fuchsin (red). The result was promising, but the agar was not dark enough. So I increased the fuchsin concentration. The agar is still in preparation. But I will tell you if its works.

If the result is not promising, I will try the sudan black.

Concerning the black cardboard, I already tried unsuccessfully this alternatives.

Thanks a lot

Alan