Neuraminidase production by Erysipelothrix rhusiopathiae. 
In order to characterise neuraminidase activity by Erysipelothrix, 85 isolates of Erysipelothrix spp.  from a variety of sources including human clinical, marine and terrestrial animals, and the environment were investigated for neuraminidase production.  Neuraminidase activity was detected by a peanut lectin haemagglutination method.  The effects of media, incubation conditions and pH on the production and activity of neuraminidase were also investigated.  Enzyme activity was detected only in the supernatants of the isolates of Erysipelothrix rhusiopathiae which had been incubated in cooked meat broth and Todd Hewitt broth supplemented with horse serum after 16 and 36 h incubation at 37 degrees C. The maximum titres were reached at 40 h in cooked meat broth and 56 h in Todd Hewitt broth supplemented with horse serum.  All 58 isolates and the type strain (ATCC 19414) of E. rhusiopathiae produced detectable neuraminidase activity with titres between 10 and 320.  The optimal pH for the enzyme activity varied among the isolates with a pH between 6.0 and 7.0 covering the highest enzyme activity of the most.  There was no statistically significant difference in the level of neuraminidase activity between isolates from different sources (p > 0.05).  Neuraminidase activity was not detected in the non-pathogenic Erysipelothrix spp.  such as E. tonsillarum.  Neuraminidase was detected only in E. rhusiopathiae suggesting its possible role as a virulence factor.  Enzyme production and activity were medium and pH dependent.  The peanut lectin haemagglutination assay is a simple, rapid and sensitive method and is particularly useful for the analysis of multiple samples.