Evidence for two haemolytic activities fromAeromonas salmonicida

Abstract

Aeromonas salmonicida is the aetiological agent of furunculosis, an economically important disease of fish, particularly salmonids reared under intensive conditions [1]. There has been much interest recently in the investigation of toxins and other pathogenic mechanisms with a view to producing effective vaccines. A factor having leukocytolytic activity has been partially characterized [2]; proteolytic activity may be responsible for the necrosis of tissue seen in infected fish [3,4]. However, the anaemic response of infected fish [5] and the presence of extensive haemosiderin deposits in haemopoietic tissue [6] have resulted in the suggestion that haemolysins may play a role in pathogenesis. Extracellular products obtained by the agar overlay technique have been shown to be toxic and contain haemolytic activity against trout erythrocytes [7]. However, the complex nature of such material is likely to make it difficult to purify the factors responsible. We report here the first detailed study of haemolysin production by A. salmonicida and present evidence for the existence of two distinct haemolytic activities.