A gelatin test to detect activity and stability of proteases produced by Dichelobacter (Bacteroides) nodosus

Previously reported tests to distinguish thermostable and thermolabile proteases of Dichelobacter nodosus used hide powder azure as a test substrate. This paper describes an alternative test for protease stability using gelatin, an inexpensive and convenient substrate. The test required less equipment and time than the hide powder tests, and simplified the testing of multiple samples. Proteases from 2965 isolates of D. nodosus from samples collected as part of a footrot eradication scheme were tested using the gelatin method, 1707 produced thermostable, and 1258 produced thermolabile protease. Production of thermostable protease was used to identify isolates of D. nodosus which had the potential to cause the virulent form of ovine footrot. Comparisons were made with a hide powder test on 47 isolates. Further characterisation of all proteases was undertaken using polyacrylamide gel electrophoresis. Isoenzyme patterns of thermostable protease producing isolates were identified as S1 (1688 isolates) and S2 (19) whilst thermolabile protease producing isolates showed patterns U1 (1104 isolates), U2 (40), U3 (32), U4 (47), U5 (6), U6 (28) and S1 (1).