particularly around the vent at the bases of the pectoral and pelvic fins and

Particularly around the vent at the bases of the

This preview shows page 326 - 328 out of 594 pages.

particularly around the vent, at the bases of the pectoral and pelvic fins, and head (Huntly et al., 1992). Erythrocyte membranes were degraded (=haemolytic activity). It was concluded that this phospholipase exhibited GCAT activity. Production of haemolysins by Aer. salmonicida may also contribute to the pathogenesis of furunculosis, insofar as it has been established that ECP contain components with pronounced haemolytic activity for trout erythrocytes (Munro et al., 1980). Titball and Munn (1981) carried out the first extensive study of haemolysin production by Aer. salmonicida. These authors reported the existence of two distinct haemolytic activities. Essentially, they determined that the supernatant from un- shaken broth cultures contained haemolytic activity against erythrocytes from a diverse range of vertebrate species, with maximal activity against horse red blood cells. Titball and Munn termed this "H" activity. If cultures were shaken, however, the resulting supernatant yielded an activity against trout erythrocytes only (this was designated the "T" activity). Furthermore, the H-lysin was reported as unstable in culture supernatants, sensitive to heat after exposure to 56°C for 5min, and became membrane-bound when solutions were filtered. In contrast, the T-lysin was stable in supernatants, and was inactivated by normal rainbow trout serum. Nomura and Saito (1982) also studied the extracellular haemolytic toxin which was recorded as cytotoxic for sheep and salmonid erythrocytes. These investigators observed that the production of haemolysin was stimulated by the addition of enzymic hydrolysates of protein, but suppressed by carbohydrates, such as glucose or sucrose. Moreover, bivalent metal ions, e.s. Ca^+, Co^+ and Mn2+, and phosphate ion ([HP04]^-) were necessary for production of the haemolysin. The optimum pH range and optimum temperature for toxin production was 7.5-8.0 and 20°C, respectively. Nomura and Saito (1982) concluded that the haemolysin was produced during the stationary phase of the growth cycle, and was relatively heat-labile, being inactivated at 60° C. These observations coincided with those of Titball and Munn (1981). In continued studies of the T- and H-lysins, Titball and Munn (1983, 1985a) purified the components, and examined properties of the haemolytic activity. Thus, the T-lysin activity was separated into two factors, namely a caseinase and another.
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Pathogenicity 307 apparently membrane-associated (Ti) activity, which by itself caused only incomplete lysis. In fact, complete lysis of trout erythrocytes occurred only in the presence of both Ti activity and the caseinase (also see Rockey et al, 1988). Titball and Munn (1983) believed that this phenomenon was due to the co-operative effect of both activities on the red blood cell membrane, rather than the conversion of T^ to T- lysin by caseinase. This opinion was reached because the inhibition of caseinase resulted in the loss of complete lytic potential from supernatant fluids containing T-lysin. Titball and Munn (1985a) regarded the H-lysin to be a proteinaceous sub- stance, on the basis of results of the ultraviolet absorption spectrum. Additionally,
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