Antigenic and cross-protection studies of biotype 1 and biotype 2 isolates of Yersinia ruckeri in rainbow trout, Oncorhynchus mykiss (Walbaum).

AIMS: The study investigated antigen characteristics of biotype (bt) 1 and bt 2 isolates of Yersinia ruckeri. METHODS AND RESULTS: The cell surface characteristics of Y. ruckeri were compared for their antigenic characteristics using polyclonal antibodies that revealed that both biotypes had a homogenous whole-cell protein antigenic profile. Notable differences in the antigenic properties were observed in the lipopolysaccharide profile of both biotypes. Two iron-regulated outer membrane proteins (IROMP) of c.90 and 100 kDa were shown to be major specific antigens. The results demonstrate for the first time differences in antigens between bt 1 and bt 2 isolates of serotype O1 isolates of Y. ruckeri. The protection induced in rainbow trout by a commercial monovalent, and bivalent inactivated vaccine was tested with the outcome that the ability of isolates to cause mortality in vaccinated fish varied with geographical location. In this context, vaccination studies suggested that the O antigen was the dominant immunogenic molecule involved in protection against the disease. CONCLUSIONS: The O antigen of Y. ruckeri was the dominant immunogenic molecule involved in the protection of rainbow trout against enteric redmouth disease. SIGNIFICANCE AND IMPACT OF THE STUDY: There are distinct phenotypic and antigenic differences in Y. ruckeri bt 1 and bt 2 with O antigen recognized as the dominant immunogenic molecule. The data have significance in explaining the lack of success of the earlier monovalent vaccine and demonstrate the effectiveness of the newer bivalent vaccine.

Novel non-motile phenotypes of Yersinia ruckeri suggest expansion of the current clonal complex theory.

The biochemical and cell surface characteristics of 63 non-motile isolates of Yersinia ruckeri from various sources were compared using the API 20E rapid identification system and conventional phenotypic methods. Eight individual phenotypic groups from a variety of fish species were observed from the data set. Non-motile isolates were not exclusively observed from serogroup O1; membership of biotype 2 was recorded for representatives from serogroups O2-O7. Variations in phenotypes highlights that new clonal groups are arising and that the current typing scheme requires expansion. Previously, it was hypothesized that disease was caused by a few virulent clones; data in this paper suggests that this assumption is not the case. The lipopolysaccharide (O antigen) type in the non-motile biotype was different from other isolates of Y. ruckeri.

Subcellular components of probiotics Kocuria SM1 and Rhodococcus SM2 induce protective immunity in rainbow trout (Oncorhynchus mykiss, Walbaum) against Vibrio anguillarum.

The efficacy of cellular components of probiotics Kocuria SM1 and Rhodococcus SM2 to protect rainbow trout (Oncorhynchus mykiss, Walbaum) against vibriosis was assessed. Groups of fish (average weight = 10-15 g) were immunized intraperitoneally (i.p.) with 0.1 ml of subcellular materials, i.e., 0.2 ± 0.05 mg protein per fish, comprising extracellular proteins (ECPs), cell wall proteins (CWPs) and whole cell proteins (WCPs) of SM1 and SM2, respectively, or with 0.1 ml of phosphate-buffered saline (PBS) to serve as the control. Seven days after administration, fish from each group were challenged i.p. with 0.1 ml of a suspension in PBS of 3 × 10(5) cells ml(-1) per fish of Vibrio anguillarum. Use of CWPs and WCPs demonstrated significantly (P < 0.05) better protection against V. anguillarum insofar as mortalities were reduced to 11-17% [relative percent survival (RPS) = 80-87%], although ECPs fared less well (mortalities = 33-38%; RPS = 56-62%; P > 0.05), compared to 86% mortalities of the controls. The mode of action reflected activation of innate immune factors by CWPs and WCPs, demonstrating significantly (P < 0.05) increased expression of respiratory burst (optical density; OD(550 nm)) from 0.039 to 0.043-0.045, peroxidase (OD(550 nm)) from 0.26 to 0.37-0.55, and bacterial killing activities (i.e., percentage of surviving bacteria reduced from 79% to 56-57% for SM2). Moreover, an elevation of leucocyte number (from 1.93% to 1.98-2.93%; P > 0.05) and immunoglubolin level (from 27 mg ml(-1) to 28.5-33 mg ml(-1); P > 0.05) were observed with the experimental groups. These results indicate that cell components of the probiotics stimulate an immune response.