3. Results and discussion
The universal assay described by Schwyn and Neilands (1997) was used for the detection of
siderophore by different microorganisms (fungi and bacteria) in solid medium. When CAS-agar plates
were prepared according to those authors most of fungi and bacteria (mainly Gram-positive) used in
this study did not grow. Lately, we changed the original methodology by preparing CAS-blue agar
plates overlaid with a layer of MEA or nutrient agar media. Again most basidiomicetes either grew
poorly or did not grow, and the Gram-positive bacteria were strongly inhibited. Thus, a procedure
for separating the CAS reagent from the growing cells was de- veloped by us and plates containing
half culture medium and half CAS-blue agar were prepared. This modification in the original CAS
assay made it possible study the siderophore production by all the microorganisms selected for this
work, with no problem of growth inhibition.