We present herein an improved assay for detecting the
presence of extracellular proteases from microorganisms on
agar plates. Using different substrates (gelatin, BSA,
hemoglobin) incorporated into the agar and varying the culture
medium composition, we were able to detect proteolytic
activities from Pseudomonas aeruginosa, Micrococcus
luteus and Serratia marcescens as well as the
influence that these components displayed in the expression
of these enzymes. For all microorganisms tested we found that
in agar-BHI or yeast extract medium containing gelatin the
sensitivity of proteinase detection was considerably greater
than in BSA-agar or hemoglobin-agar. However, when BSA or
hemoglobin were added to the culture medium, there was an
increase in growth along with a marked reduction in the amount
of proteinase production. In the case of M. luteus the
incorporation of glycerol in BHI or yeast extract gelatin-agar
induced protease liberation. Our results indicate that the
technique described here is of value for detecting
extracellular proteases directly in the culture medium, by
means of a qualitative assay, simple, inexpensive, straight
forward method to assess the presence of the proteolytic
activity of a given microorganism colony with great freedom in
substrate selection.
