Experimentally induced marine flexibacteriosis in Atlantic salmon smolts Salmo salar. I. Pathogenicity

Abstract

Tenacibaculum maritimum causes marine flexibacteriosis in many cultured fish species, including Atlantic salmon Salmo salar in Tasmania, Australia. Several aspects of the pathogenicity of this bacterium were investigated in naive Atlantic salmon smolts using different isolates, growth conditions and doses to produce a model of infection. We found that T. maritimum is pathogenic to Atlantic salmon using either marine Shieh's or marine Ordal's culture medium. The use of aeration in broth culture produced a dose effect in challenge due to a 'clumping' of the bacteria during culture. The virulence of a strain appears to be connected with this 'clumping'; the more adherent the cells, the more pathogenic the strain. Differences in virulence between 3 strains was apparent, with 1 of the strains (89/4747) being non-pathogenic and unable to produce disease in the host. The 2 other strains (89/4762, 00/3280) were highly virulent, resulting in 100% mortalities within 3 d. A reproducible model of infection has been established in the present study using strain 89/4762. Results from the present study provide a better insight into the nature of the disease. KEY WORDS: Tenacibaculum maritimum · Pathogenicity · Atlantic salmon · Infection model Resale or republication not permitted without written consent of the publisherDis Aquat Org 91: [121][122][123][124][125][126][127][128] 2010 MATERIALS AND METHODSPathogenicity experiments. Three different methods were used to assess the pathogenicity of Tenacibaculum maritimum in Atlantic salmon (Table 1). Expt 1 was a comparison of methods: 2 different growth media, marine Shieh's broth (MSB) and marine Anacker and Ordal's broth (Anacker & Ordal 1959) (MOB), with or without aeration were used during culture of bacteria. The assessment was made with strain 89/4762. Expt 2 was a comparison of the pathogenicity of 3 strains (89/4762, 89/4747, 00/3280) and Expt 3 compared dose effects for 1 strain (89/4762). Assessments of culture media and strains on pathogenicity were made in a semi-static experiment. As a recirculation system was used in Expt 3, there were 2 different control treatments. One control treatment was within the recirculation system and was called control (in); and another was still part of the system but had a separate water source, and was called control (out). The system was set up with a filter bank down to 0.8 µm for incoming water and 2 UV lights (400 J m 2-1 , 4000 l h -1 ) to reduce bacterial load.Experimental fish. Naive, disease-free Atlantic salmon smolts were obtained from a commercial hatchery. The fish were initially kept in freshwater and then acclimated to seawater (salinity 35) over a week starting at salinity 5. They were fed on a commercial diet (Atlantic HP, Skretting) at maintenance (1% body weight) during acclimation. Feeding ceased 48 h before challenge. Numbers of fish and replicates, weight and length of the fish, and water conditions for each experiment are summarised in Table 2.Bacteria cultures. Three strains of Tenacibaculum marit...

Morphopathological features of a severe ulcerative disease outbreak associated with Tenacibaculum maritimum in cultivated sole, Solea senegalensis (L.)

“…Unlike other skin conditions that occur with a high number of ulcers distributed anywhere on the body surface (Wiklund & Bylund 1993;Roberts 2001;Austin & Austin 2007;Bruno et al 2007;Kodama, Denso & Nakagawa 2007), in the present study, no more than 2-3 severe ulcerative lesions, mainly located in the fins, were observed in the same fish. Other gross pathological findings previously recorded (Carson, McCosh & Schmidtke 1992;Handlinger et al 1997;van Gelderen et al 2011) in Atlantic salmon naturally or experimentally infected with T. mari- timum, such as erosion of the oral cavity and jaws, eye damage or gill necrosis, were not observed in the current study, even in severely affected sole. These findings are consistent with the chronic form of the disease described in Atlantic salmon by van Gelderen et al (2011) using a dose-dependent infectious trial.…”

Experimental induction of mouthrot in Atlantic salmon smolts using Tenacibaculum maritimum from Western Canada

“…The temperature of 12°C used in all the experiments is much lower than previously performed challenge studies involving T. maritimum . This is particularly relevant when comparing to other experiments previously performed with Atlantic salmon smolts, where temperatures up to 20°C were used (Handlinger et al., ; Soltani et al., ; van Gelderen et al., , ). These higher temperatures are at the upper range of optimal rearing conditions for Atlantic salmon smolts, which may have had an influence on results (Jonsson, Forseth, Jensen, & Næsje, ).…”

“…In Tasmania, Australia, T. maritimum has been linked to tenacibaculosis in Atlantic salmon smolts. This disease has been reproduced in the laboratory by bath infecting fish for a short period of time (1 hr) at a high concentration (Handlinger et al., ; Soltani, Shanker, & Munday, ; Soltani et al., ; van Gelderen et al., ; van Gelderen, Carson, & Nowak, ). These experiments also showed that Atlantic salmon was more susceptible than rainbow trout ( Oncorhynchus mykiss , Walbaum) and that exposure at lower salinities (15 ppt) gave very low mortality (Handlinger et al., ; Soltani et al., ).…”

Physical characterisation of Tenacibaculum maritimum for vaccine development

“…Using the phenotypic markers described, the isolates were grouped and ranked in order to make selections for later pathogenicity and vaccination trials (van Gelderen et al. 2009, in press).…”