Flexibacter MaritimusAssociated with a Bacterial Stomatitis in Atlantic Salmon Smolts Reared in Net-Pens in British Columbia

Filamentous yellow-pigmented bacteria (YPB) were consistently isolated from outbreaks of bacterial stomatitis (“mouth rot”) affecting smolts of Atlantic salmon Salmo salar after seawater entry in British Columbia. Six representative YPB isolates were selected, and phenotypic characterization demonstrated that they shared morphological, physiological, and biochemical similarities with the Flexibacter maritimus reference strains ATCC 43397 and ATCC 43398T (type strain). Polyclonal antisera raised against one British Columbia mouth rot isolate (MRJ) and strains ATCC 43397 and ATCC 43398T were used to examine the antigenic relationships between the YPB from British Columbia and these reference strains. Using agglutination, immunodiffusion, and western immunoblots, it was demonstrated that the British Columbian YPB were antigenically related to ATCC 43397 and ATCC 43398T. Furthermore, immunohistochemistry indicated that the filamentous YPB recovered from outbreaks of mouth rot were antigenically related to those seen histologically. Taken together, it was concluded that these YPB recovered from Atlantic salmon mouth rot in British Columbia are strains of F. maritimus.