Serological and Molecular Typing of Tenacibaculum Maritimum from New Zealand Farmed Salmon, Oncorhynchus Tshawytscha

Tenacibaculum maritimum is a cosmopolitan bacterial pathogen with the potential to cause significant losses in a broad range of farmed and wild marine fish species. This study investigated the antigenic diversity of T. maritimum isolated in culture from farmed Chinook (king) salmon (Oncorhynchus tshawytscha) from the Marlborough Sounds in New Zealand. A total of 36 isolates were examined using antibody serotyping and rapid molecular serotyping via multiplex PCR (mPCR) targeting genes encoding O-antigen biosynthesis enzymes. Serological analysis using three different polyclonal antisera developed against T. maritimum isolated from farmed Atlantic salmon (Salmo salar) in Tasmania, Australia revealed that there are three putative serotypes of T. maritimum that occur in New Zealand. The predominant serotype was defined by a positive reaction to all three Tasmanian antisera (antisera A, B and C), designated as serotype ABC. This serotype was found at all nine farm locations tested and represented 81% of all isolates examined. The same library of isolates was evaluated by mPCR serotyping and found three O-AGC types among tested isolates. O-AGC Type 3 was not only the predominant type (72%) present, but it also had a wide distribution, having been isolated at eight of the nine farms. Two other O-AGC types (O-AGC Type 2–1 and O-AGC Type 3–2) were identified, providing evidence of genetic variation. However, there was only partial concordance between the two serotyping techniques, which is likely linked to differences in the way serotypes are defined in the two approaches that were used. Nevertheless, in broad terms there is good evidence of intraspecific antigenic variation within our library of isolates, and collectively these data will be of crucial importance for assessing the pathogenicity of the isolates and the subsequent development of a vaccine for this emerging disease in New Zealand marine salmon farms.