Assessment of gelatin gel and elastase tests for detection of protease activity of Dichelobacter nodosus isolates from ovine footrot.

Protease tests (the gelatin gel protease thermostability test, the elastase test or both) were performed on 4296 isolates of Dichelobacter nodosus derived from 452 outbreaks of ovine footrot occurring in New South Wales. Both tests showed a high level of repeatability. In the gelatin gel test, culture broths were heated for 16 min at 66.8 degrees C. Heated broths containing thermostable protease digested gelatin (positive gelatin gel test) while those broths containing thermolabile protease failed to digest gelatin (negative gelatin gel test). Gelatin gel positive isolates were unable to be graded into subcategories on the basis of the percentage stability of their protease. In the elastase test, the ability of isolates to digest (positive elastase test) or not digest elastin particles (negative test) was measured up to 28 days incubation. Individual elastase positive isolates yielded a graded result based on the number of days to reach a positive result. There was a very high level of agreement between the gelatin gel and the elastase tests consistent with their separating isolates into two groups based on protease activity (either gelatin gel positive and elastase positive or gelatin gel negative and elastase negative). Either test is suitable for use in footrol control and eradication schemes. The gelatin gel test provides clearcut separation of isolates into positive and negative categories and has the major advantage of yielding a more rapid result than the elastase test. The elastase test should be utilised where a graded assessment of protease activity is desired.