A comparison of different methods for determining elastase activity of Pseudomonas aeruginosa strains from mink

We have characterized 20 Pseudomonas aeruginosa strains isolated from pneumonic mink lungs with regard to elastase production and serotype. P. aeruginosa PAO1, a well-characterized elastase-producing strain, and two elastase-deficient mutants of PAO1 were used for comparative purposes. Elastase activity was assayed on elastin agar and by using 14C-elastin coated microtiter plates. Elastase antigen was measured using a double antibody sandwich ELISA (enzyme-linked immunosorbent assay). Total proteolytic activity was determined on skim milk agar plates. The results from ELISA showed that all strains produced antigenically similar elastase, although the amounts produced varied considerably between strains. There was a good correlation regarding elastase assays between ELISA and 14C-elastin, elastin agar and total proteolytic activity on skim milk agar. No correlation was found between serotype and elastase activity. The results showed that the 14C-elastin assay is a simple and sensitive method of determining elastolytic activity of P. aeruginosa strains.