Vibrio anguillarumResistance to Rainbow Trout (Oncorhynchus mykiss) Serum: Role of O-Antigen Structure of Lipopolysaccharide

Abstract

The sensitivity of Vibrio anguillarum to the bactericidal effect of rainbow trout serum was investigated with different strains of serogroups O1 and O2a, which are the most frequently found serogroups in clinical outbreaks of vibriosis. All of the V. anguillarum strains were able to activate complement in rainbow trout serum, but smooth strains of V. anguillarum serogroup O1 were resistant to complement-mediated killing in the absence of specific antibodies. In the case of V. anguillarum serogroup O2a strains, 80% of the analyzed strains were resistant to rainbow trout serum even when specific antibodies were present. Analysis of the lipopolysaccharide structures of the tested V. anguillarum strains showed a positive correlation between the O-antigen size of the lipopolysaccharide and resistance to serum killing. The classical complement pathway was responsible for the antibody-dependent serum killing of susceptible V. anguillarum strains. When serum-resistant V. anguillarum serogroup O2a strains were grown in glucose-enriched Lennox L broth, they produced lipopolysaccharide molecules with fewer high-molecular-weight O-antigen units than did strains grown in broth without the addition of glucose. Strains grown in glucose-enriched medium became sensitive to rainbow trout serum killing, indicating that the high-molecular-weight O-antigen side chains prevented the activated complement from damaging the bacterium.

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

“…Although bt 2 isolates possessed a different overall structure, no correlation in virulence could be established. Of relevance, it has been demonstrated by Boesen et al (1999) that virulent isolates of Vibrio anguillarum, which possessed a smooth LPS structure, were resistant to serum killing. However, unlike mammals, fish appear to be immune to the septic shock effects of LPS (MacKenzie et al 2010).…”

Flavobacterium psychrophilum infections in salmonid fish

“…The results showed that both virulent and non-virulent F. psychrophilum were resistant to the action of the complement activity present in the rainbow trout serum. Whether this serum resistance is mediated by the presence of LPS and a polysaccharide capsule, as has been demonstrated for other fish pathogens Boesen et al 1999), remains to be elucidated.…”

Mutational analysis of the zinc metalloprotease EmpA ofVibrio anguillarum

“…Vibriosis causes a high mortality in infected fish and is responsible for great losses in aquaculture (Egiduis, 1987). The diverse products secreted by V. anguillarum have been reported as being associated with its pathogenesis, such as the iron-uptake system (Crosa, 1980), hemolysin (Kodama et al, 1984), lipopolysaccharide (LPS) (Norqvist & Wolf-Watxtz, 1993;Boesen et al, 1999) and cytotoxin (Kodama et al, 1985). In addition, the extracellular zinc metolloprotease, EmpA, was also identified as an important factor in virulence, as it helps bacterial pathogens to enter host cells (Inamura et al, 1985;Norqvist et al, 1990;Farrell & Crosa, 1991).…”