Use of elastase test, gelatin gel test and electrophoretic zymogram to determine virulence of Dichelobacter nodosus isolated from ovine foot rot

A comparative study using the elastase test, gelatin gel test and electrophoretic zymogram was conducted for virulence determination of 96 Dichelobacter nodosus isolates from clinical cases of ovine foot rot. Despite being time consuming, the elastase test provided a classification of D nodosus bacteria in general agreement with the severity of clinical characteristics. The gelatin gel test showed some correlation with the elastase test. While isolates showing elastase activity at 14 days or less were likely to produce more proteases which were of higher thermostability, those showing elastase activity at 21 to 28 days, or elastase negative up to 28 days tended to produce less proteases which were also of lower thermostability. The electrophoretic zymogram based on the virulent pattern 1 (V1), virulent pattern 2 (V2) and benign pattern (B) did not cover all isolates from the field as nine (9·4 per cent) of the 96 isolates formed specific isoenzyme patterns that were different from the V1, V2 and B patterns of classification. However, the patterns formed by these nine isolates could be fitted into another previously reported isoenzyme classification. Nevertheless, the electrophoretic zymogram by itself did not provide adequate information in regard to intermediate foot rot. It appeared that a combination of two tests such as elastase test and zymogram or gelatin gel test and zymogram would offer a useful complementary definition of the virulence of D nodosus bacteria.