This media tests for the ability of an organism to break down and use a vegetable lipid (tributyrin) present in the agar plates. If an organism is able to secrete lipase the lipid can be hydrolysed. The media usually contains spirit blue or methylene blue as an indicator. Use of the lipid can be observed as a zone of clearing around areas of growth. The zone has to be transparent for the test to be considered positive; color changes are not considered to be positive.