Cross‐protection of a live‐attenuated Flavobacterium psychrophilum immersion vaccine against novel Flavobacterium spp. and Chryseobacterium spp. strains

Abstract

For salmonid producers, a common threat is Flavobacterium psychrophilum. Recent advancements in bacterial coldwater disease (BCWD) management include the development of a live‐attenuated immersion vaccine that cross‐protects against an array of F. psychrophilum strains. Emerging family Flavobacteriaceae cases associated with clinical disease have been increasing, including pathogenic isolates of Flavobacterium spp. and Chryseobacterium spp. The cross‐protective ability of a live‐attenuated F. psychrophilum vaccine was determined against three virulent Flavobacteriaceae isolates. Juvenile rainbow trout were vaccinated, developed high F. psychrophilum‐specific antibody titres and were challenged with Chryseobacterium spp. isolates (S25 and T28), a Flavobacterium sp. (S21) isolate, a mixed combination of S21:S25:T28, and a standard virulent F. psychrophilum CSF259‐93 strain. Results demonstrated strong protection in the CSF259‐93 vaccinated group (relative per cent survival (RPS)=94.44%) when compared to the relevant CSF259‐93 controls (p < .001). Protection was also observed for vaccinated fish challenged with the S21:S25:T28 mix (RPS = 85.18%; p < .001). However, protection was not observed with the S21, S25 or T28 isolates alone. Analysis of whole‐cell lysates revealed differences in protein banding by SDS‐PAGE, but conserved antigenic regions by Western blot in S25 and T28. Results demonstrate that this live‐attenuated vaccine provided protection against mixed flavobacterial infection and suggest further benefits against flavobacteriosis.

Atypical flavobacteria recovered from diseased fish in the Western United States

“…Successful vaccination against flavobacterial disease is another challenge complicated by the high diversity of piscine pathogenic species and the propensity for mixed species outbreaks. Recent studies with a live-attenuated vaccine against F. psychrophilum have shown some promising preliminary results for cross-protection and conserved antigens between F. psychrophilum and atypical Flavobacterium and Chryseobacterium isolates (Bruce et al, 2020), but there remains much work to be completed to reach targets for widespread protection.…”

“…Infected fish often display signs mimicking those caused by established etiologic agents, including skin ulceration, fin erosion, and gill necrosis (Loch and Faisal, 2016b;Jung et al, 2022;Malick et al, 2022). Additionally, fish may be concurrently infected by more than one species, and atypical flavobacteria may not be easily distinguished by conventional diagnostic methods (Bernardet et al, 2005;Bruce et al, 2020). Current limitations in epidemiological and pathological data obfuscate the risk these potential pathogens pose to aquaculture.…”

Genetic diversity and phenotypic characterization of Iodobacter limnosediminis associated with skin lesions in freshwater fish

“…and Flavobacterium sp. (Bruce et al, 2020). Further studies are needed to determine environmental circumstances, the route of invasion and proteolytic/cytotoxic activity of I. limnosediminis, to study whether it has similar affect on fish as for example F. psychrophilum (Iturriaga et al, 2017;Ostland et al, 2000).…”

Advancements in Fish Vaccination: Current Innovations and Future Horizons in Aquaculture Health Management

“…Moreover, it has led to the formulation of the B.17-ILM vaccine, a live attenuated vaccine that protects against F. psychrophilum in salmonids and rainbow trout [71,72]. The vaccine is composed of a rifampicin resistant strain of F. psychrophilum, has considerable research supporting its protection potency, and is currently undergoing trials so that it can become licensed and commercialized in the US [72][73][74].…”