Pathogenic activities of live cells and extracellular products of the fish pathogen Pasteurella piscicida

Abstract

The pathobiological activities in aiuo and in uifro of live cells and extracellular products (ECP) of eleven Pasteurellu piscicida strains of different origin were examined. Infectivity trials showed that P. piscicida did not possess strict host specificity since the majority of the isolates were virulent for gilthead seabream, rainbow trout and turbot, with LDS0 values ranging between lo3 and lo6 live cells. However, none of the strains tested were pathogenic for mice (LD5,, > lo* cells). In addition, the ECP were strongly toxic for fish (LDS0 ranging from 1-0 to 4.6 pg protein per g fish), which clearly demonstrates their important role in the pathogenesis of pasteurellosis.All the ECP samples were cytotoxic for fish and homoiothermic cell lines, possessed notable phospholipase activity and displayed haemolytic activity for sheep, salmon and turbot erythrocytes (but not for trout erythrocytes).However, the production of proteolytic enzymes differed among the P. piscicidu strains. Although no strain displayed elastase activity, five isolates (the Japanese and Italian strains) hydrolysed casein and gelatin. All these biological activities in uiuo and in uifru were lost after heat treatment (100 "C for 10 min). The general enzymic patterns of both live cells and ECP evaluated by the API-ZYM system also revealed some variation among the P. piscicida isolates. Generally, whole cells showed a wider range of enzymic activities than ECP. The results presented here are important for the selection of strains in the development of effective polyvalent pasteurellosis vaccines containing both whole cells and ECP.

Sequential pathology of experimental pasteurellosis in gilthead seabream Sparus aurata. A light- and electron-microscopic study

“…The presence of numerous degenerate erythrocytes in the blood or phagocytosed by macrophages corroborates the presence of the haemolytic activity demonstrated in vitro (Magarifios et al 1992). However, the reduction in the number of circulating erythrocytes in fish injected with Pasteurella piscicida was not significant.…”

“…The lethal dose (LDS,) of the strain for this fish species was 1.6 X cells fish-' (Toranzo et a!. 1991, Magarifios et al 1992. Cultures were stored frozen at -70°C in Tryptic Soy Broth (TSB, Difco) with 15% (v/v) glycerol until use.…”

In vitro killing of Pasteurella piscicida by fish macrophages

“…Strain DI-21 was isolated from gilthead sea bream in Spain and strain EPOY-8803-11 from red grouper Epinephelus akaara in Japan. Both isolates had previously been tested for pathogenicity in trout and gilthead sea bream; DI-21 was established as pathogenic (LDSo values ranging between 103 and 105) and EPOY-8803-11 as non-pathogenic (LD5" > 2 X 10') for both fish species (Toranzo et al 1991, Magarinos et al 1992.…”

Viability of starved Pasteurella piscicida in seawater monitored by flow cytometry and the effect of antibiotics on its resuscitation

“…This strain proved to be pathogenic for fish with a lethal dose (LD 50 ) the propidium iodide. All the measurements were carried out in triplicate and data were statistically analysed by the LYSIS ranging from 10 3 to 10 5 depending on the fish species tested (Magariños et al 1992).…”

“…The FCM experiments for assessing the viability of micro-organism was first isolated from natural populations of Past. piscicida cells were based on the membrane integrity white perch (Morone americanus) and striped bass (Morone analysis, using the fluorescent intercalating dye propidium saxatilis) in the early 1960s (Sniezsko et al 1964), but the iodide, and the study of the accumulation of rhodamine 123 disease has now a world-wide distribution and a diverse host since, under appropriate conditions, the extent to which indirange (Toranzo et al 1991 ;Kusuda and Salati 1993).…”