Advancements in Characterizing Tenacibaculum Infections in Canada

Abstract

Tenacibaculum is a genus of gram negative, marine, filamentous bacteria, associated with the presence of disease (tenacibaculosis) at aquaculture sites worldwide; however, infections induced by this genus are poorly characterized. Documents regarding the genus Tenacibaculum and close relatives were compiled for a literature review, concentrating on ecology, identification, and impacts of potentially pathogenic species, with a focus on Atlantic salmon in Canada. Tenacibaculum species likely have a cosmopolitan distribution, but local distributions around aquaculture sites are unknown. Eight species of Tenacibaculum are currently believed to be related to numerous mortality events of fishes and few mortality events in bivalves. The clinical signs in fishes often include epidermal ulcers, atypical behaviors, and mortality. Clinical signs in bivalves often include gross ulcers and discoloration of tissues. The observed disease may differ based on the host, isolate, transmission route, and local environmental conditions. Species-specific identification techniques are limited; high sequence similarities using conventional genes (16S rDNA) indicate that new genes should be investigated. Annotating full genomes, next-generation sequencing, multilocus sequence analysis/typing (MLSA/MLST), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF), and fatty acid methylesters (FAME) profiles could be further explored for identification purposes. However, each aforementioned technique has disadvantages. Since tenacibaculosis has been observed world-wide in fishes and other eukaryotes, and the disease has substantial economic impacts, continued research is needed.

Keywords: Tenacibaculum; aquaculture; bivalves; fishes; tenacibaculosis.

Figure 1

Histology of an Atlantic salmon (Salmo salar) with mouthrot in British Columbia (Canada). Top: There is extensive ulceration of the mucosal epithelium with thick basophilic plaques (A–C) and marked diffuse inflammation of the dermis (*). Bottom: A magnified portion of a tooth and a plaque of filamentous bacteria (B), where bacteria are seen disseminating into surrounding tissues with surrounding macrophages, necrotic cells, and fibrin and with disruption of connective tissue (black square). Optimization of photomicrograph illumination and color balance followed published methods [124] and was provided by G. M. Marty.

Figure 2

Clinical presentation of mouthrot in Atlantic salmon (Salmo salar) in British Columbia (Canada). (A–C): Yellow plaques (arrow) on the pre-maxilla, maxilla, and palatine teeth. (D,E) Yellow plaques (arrow) on the gill-raker or the gill filaments, while discoloration, clumping, and hemorrhaging of the filaments is also present. F: Two yellow plaques (arrow) on the flank on the fish. Pictures are courtesy of the Fish Health Team of Mowi Canada West.