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Tenacibaculum maritimum is the aetiological agent of an ulcerative disease known as tenacibaculosis, which affects a large number of marine fish species in the world and is of considerable economic significance to aquaculture producers. Problems associated with epizootics include high mortality rates, increased susceptibility to other pathogens, high labour costs of treatment and enormous expenditures on chemotherapy. In the present article we review current knowledge on this bacterial pathogen, focusing on important aspects such as the phenotypic, serologic and genetic characterization of the bacterium, its geographical distribution and the host species affected. The epizootiology of the disease, the routes of transmission and the putative reservoirs of T. maritimum are also discussed. We include a summary of molecular diagnostic procedures, the current status of prevention and control strategies, the main virulence mechanisms of the pathogen, and we attempt to highlight fruitful areas for continued research. TAXONOMYThe taxonomy of Tenacibaculum maritimum was a matter of controversy and confusion for decades, and it has only recently been clarified by Suzuki et al. (2001). Masumura & Wakabayashi (1977) isolated a gliding bacterium that had caused mass mortalities among certain cultured marine fish. These strains were characterized by Hikida et al. (1979), who announced their intention to make a separate formal proposal of the name Flexibacter marinus. Since the epithet marinus had already been used in the name Vibrio marinus, the authors changed their mind on the use of this epithet, and the eventual formal proposal was a taxon called Flexibacter maritimus (Wakabayashi et al. 1986, Holmes 1992. Reichenbach (1989) listed the pathogen as Cytophaga marina, but the priority of the name Flexibacter maritimus was later recognized (Holmes 1992). These results were confirmed by Bernardet & Grimont (1989), who also validated the name Flexibacter maritimus based on DNA-DNA hybridisation methods.However, the resolution of phenotypic characterization and 16S ribosomal RNA (rRNA) sequence analysis is insufficient to distinguish closely related organisms. Thus, Suzuki et al. (2001), based on the nucleotide sequence of the gyrB, proposed that Flexibacter maritimus should be transferred to the new genus Tenacibaculum, in which 7 members are currently included. Table 1 shows the main differential characteristics of the described species of the genus Tenacibaculum. GEOGRAPHICAL DISTRIBUTION AND HOST SPECIESThe geographical distribution of Tenacibaculum maritimum in wild and farmed fish is shown in Table 2. 256 Characteristic T. maritimum T. ovolyticum T. mesophilum T. amilotyticum T. skagerrakense T. lutimarisOrigin Diseased red sea Halibut egg, Sponge and Macroalgae, Pelagic, Tidal flat, bream fingerling, Japan Norway macroalgae, Japan Japan Denmark Korea Cells size (µm) 2-30 × 0.5 2-20 × 0.5 1.5-10 × 0.5 2-4 × 0.4 2-15 × 0.5 2-10 × 0. Percentage of NaCl in the medium Table 1. Differential phenotypic characteris...

Tenacibaculum maritimum is the etiological agent of marine flexibacteriosis disease, with the potential to cause severe mortalities in various cultured marine fishes. The development of effective preventive measures (i.e. vaccination) requires biochemical, serological and genetic knowledge of the pathogen. With this aim, the biochemical and antigenic characteristics of T. maritimum strains isolated from sole, turbot and gilthead sea bream were analysed. Rabbit antisera were prepared against sole and turbot strains to examine the antigenic relationships between the 29 isolates and 3 reference strains. The results of the slide agglutination test, dot-blot assay and immunoblotting of lipopolysaccharides (LPS) and membrane proteins were evaluated. All bacteria studied were biochemically identical to the T. maritimum reference strains. The slide agglutination assays using O-antigens revealed cross-reaction for all strains regardless of the host species and serum employed. However, when the dot-blot assays were performed, the existence of antigenic heterogeneity was demonstrated. This heterogeneity was supported by immunoblot analysis of the LPS, which clearly revealed 2 major serological groups that were distinguishable without the use of absorbed antiserum: Serotypes O1 and O2. These 2 serotypes seem to be host-specfic. In addition, 2 sole isolates and the Japanese reference strains displayed cross-reaction with both sera in all serological assays, and are considered to constitute a minor serotype, O1/O2. Analysis of total and outer membrane proteins revealed that all strains share a considerable number of common bands that are antigenically related.

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ABSTRACT:The antibacterial activity present in the s k~n mucus of turbot Scophthalmus maximus, seabream Sparus aurdtd and seabass Dicentrarchus labrdx against Pasteul-ella piscicida and Flex~bac-ter maritimus was evaluated. Using assays on agar plates, none of the mucus samples from the above fish showed any antibacterial activity against E maritimus isolates. Turbot mucus inhibited the growth of the P piscicida but mucus from seabream and seabass did not. Assays in liquid systems to determine the survival of the above pathogens In the presence of skin mucus corroborated the results obtained by the agar plate method. The bactericidal properties of the mucus were lost after heat treatment at pH 3.5 and all skin mucus samples displayed act~vity against Staphylococcus aureus ATCC 25923, a straln resistant to lysozyme. These findings indicated that thermolabile substances other than lysozyme were responsible for the antibacterial activity in mucus of marine fish. Enzymatic and heat treatments of the mucus also showed that factors other than complement were involved and that the active component(s) was likely a glycoprotein. Regardless of the source of isolation and degree of virulence, all P piscicida and E maritimus strains adhered strongly to the skin mucus of the 3 fish species tested. Taking all of the foregoing results into consideration, it appears that whereas a possible portal of entry for E maritlmus Into the fish body is the skin, in P piscicida another pathway must be involved.

The pathobiological activities in aiuo and in uifro of live cells and extracellular products (ECP) of eleven Pasteurellu piscicida strains of different origin were examined. Infectivity trials showed that P. piscicida did not possess strict host specificity since the majority of the isolates were virulent for gilthead seabream, rainbow trout and turbot, with LDS0 values ranging between lo3 and lo6 live cells. However, none of the strains tested were pathogenic for mice (LD5,, > lo* cells). In addition, the ECP were strongly toxic for fish (LDS0 ranging from 1-0 to 4.6 pg protein per g fish), which clearly demonstrates their important role in the pathogenesis of pasteurellosis.All the ECP samples were cytotoxic for fish and homoiothermic cell lines, possessed notable phospholipase activity and displayed haemolytic activity for sheep, salmon and turbot erythrocytes (but not for trout erythrocytes).However, the production of proteolytic enzymes differed among the P. piscicidu strains. Although no strain displayed elastase activity, five isolates (the Japanese and Italian strains) hydrolysed casein and gelatin. All these biological activities in uiuo and in uifru were lost after heat treatment (100 "C for 10 min). The general enzymic patterns of both live cells and ECP evaluated by the API-ZYM system also revealed some variation among the P. piscicida isolates. Generally, whole cells showed a wider range of enzymic activities than ECP. The results presented here are important for the selection of strains in the development of effective polyvalent pasteurellosis vaccines containing both whole cells and ECP.

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