The non‐specific activation of rainbow trout, Salmo gairdneri Richardson, complement by Aeromonas salmonicida extracellular products and the correlation of complement activity with the inactivation of lethal toxicity products

Abstract

The possible mechanism of inactivation of the toxieity of Aeromonas salmonicida extracellular products (ECP) by normal rainbow trout serum was investigated using juvenile rainbow trout. ECP was prepared from culture supernatant by an acetone precipitation method. The ECP was incubated with normal rainbow trout serum at 20°C for 2 h, and the interrelationship between ECP proteolytic activity and immune complex-initiating, haemolytic complement activity (CH50) of normal serum against antibody-sensitized goldfish red blood cells was evaluated. When normal serum was incubated with increasing concentrations of ECP, the CH50 activity of serum decreased. The CH50 activity was completely abolished in serum treated with undiluted ECP. ECP treated with serum was administered to trout intraperitoneally to determine mortality. All the fish receiving untreated ECP (0-05 ml = 0-5 mg protein) alone died within 24 h. When ECP was treated with serum at 1:1 to 4:1 (serum: ECP) in volume a similar high mortality was produced. These inocula possessed high protease activity and no or low CH50 activity. However, mortality decreased and finally no mortality was recorded as ECP was treated with large volumes of serum (9:1 to 19:1). These inocula had lower protease activity and considerably higher CHso activity. Fish receiving ECP treated with heat-inactivated serum at 19:1 showed 100% mortality. A serum: ECP inoculum derived from fish which had been administered lipopolysacchadde from Salmonella enteritidis and which possessed a low CHoo activity also gave a high mortality when used at 19:1. These results suggest that rainbow trout complement is implicated in the inactivation of toxieity of A. salmonicida ECP.

Spontaneous bactericidal and complement activities in serum of rainbow trout (Oncorhynchus mykiss) genetically selected for resistance or susceptibility to furunculosis

“…In salmonids, cogent observations have been reported with the parasite C. salmositica (Wehnert & Woo, 1980;Bower & Evelyn, 1988), Vibrio anguillarum (Trust et al, 1981), and A. salmonicida (Sakai, 1984). In all cases, inactivation of the pathogen or of its virulence factors were e#ective in the absence of specific antibodies, and such was the case, too, in our experiments.…”

“…Evidence for the existence of the alternative pathway in salmonids was reported by Nonaka et al (1981), Iida & Wakabayashi (1983) and Sakai (1983). Although its e$cacy against virulent organisms has sometimes been questioned (Ourth & Bachinski, 1987;Jenkins et al, 1991), it is suspected to play a protective role in serious infections caused by the flagellate Cryptobia salmositica (Wehnert & Woo, 1980;Bower & Evelyn, 1988) and the bacterium Aeromonas salmonicida (Sakai, 1984).…”

The role of extracellular protease produced by Vibrio anguillarum.

“…In the present study, bactericidal activity of eel serum was decreased by the treatment with protease (Table 4). The same phenomenon was reported by SAKAI (1984), who demonstrated that hemolytic activity (CH50) of rainbow trout serum was considerably reduced by treatment with A. salmonicida protease. The depletion of complement induced by the protease may play a part in increasing susceptibility of Japanese eel to V. anguillarum (Table 1).…”

“…Recently various virulence factors of Aeromonas salmonicida, the causative agent of fish furun culosis, have been investigated and the roles of its protease in the pathogenesis of the infection were also examined (SAKAI, 1984(SAKAI, , 1985bTITBALL, 1985;FYFE et al, 1986). These volumi nous studies were thought to be carried out due to the incompletion of effective vaccine.…”

The trapping of intravenously injected extracellular products fromAeromonas salmonicidain head kidney and spleen of vaccinated and nonvaccinated Atlantic salmon,Salmo salarL.

“…Activation of the alternative pathway can also be mediated in vitro by extracellular products from the salmonid pathogen Aeromonas salmonicida (Sakai, 1984a).…”