No abstract

A psychrotrophic Ffexiibacter sp., Flexibacter ovolyticus sp. nov., was isolated from the adherent bacterial epiflora of Atlantic halibut (Hippoglossus hippoglossus L.) eggs and was shown to be an opportunistic pathogen for halibut eggs and larvae. The strains which we isolated had the enzymatic capacity to dissolve both the chorion and the zona radiata of the egg shells. A total of 35 isolates were characterized by using morphological and biochemical tests. These strains were rod shaped, gram negative, Kovacs oxidase positive, and pale yellow and exhibited gliding motility, They did not produce acid from any of the wide range of carbohydrates tested. Our isolates had the ability to degrade gelatin, tyrosine, DNA, and Tween 80. Starch, cellulose, and chitin were not degraded. The strains were catalase and nitrate reductase positive, did not produce H,S, and did not grow under anaerobic conditions. F. ovofyticus resembles Ffexiibacter maritimus, but differs from the latter species in several biochemical and physiological characteristics. DNAs from F. ovofyticus strains had guanine-pluscytosine contents which ranged from 30.3 to 32.0 mol% (strains EKC001, EKD002T [T = type strain], and VKB004), and DNA-DNA hybridization studies revealed levels of relatedness between F. ovoZyticw EKD002T and F. maritimus NCMB 2154T and NCMB 2153 of 42.7 and 30.0%, respectively. Compared with previously described CytophQga and FZexibacter spp. with low guanine-plus-cytosine contents, F. ovofyticus constitutes a new species. Strain EKD002 (= NCIMB 13127) is the type strain of the new species.

In intensive aquaculture systems, high mortalities are frequently observed during the early life stages of marine fish. The aim of this study was to investigate differences in the susceptibility of turbot Scophthalmus maximus, halibut Hippoglossus hippoglossus and cod Gadus morhua to various strains of Vibrio anguillarum (serotypes O1, O2α and O2β), V. salmonicida and V. splendidus. The bath challenge experiments were performed using a multidish system, with 1 egg well -1. Unchallenged eggs and larvae were used as controls. Larvae in challenged groups that suffered high mortality rates were examined by immunohistochemistry. The overall results with respect to mortality showed that the O2α serotype was pathogenic to all 3 species, while the O1 serotype was pathogenic to halibut and cod. The immunohistochemical examinations revealed differences in histopathology. The O1 serotype produced more severe and highly developed infections than the O2α serotype. In larvae exposed to the O1 serotype, necrosis and bacterial cells were seen in the dermis, gastrointestinal tract, brain and eye area, while in larvae exposed to the O2α serotype, bacteria were usually limited to the gastrointestinal tract. These results suggest either that there are undetermined species differences in host immunity or that these pathogens are host-specific even in the early life stages of fish. The O2β strain did not cause an increased mortality to halibut and turbot.

A Francisella strain, GM2212, previously isolated from moribund farmed Atlantic cod (Gadus morhua) in Norway, is closely related to Francisella philomiragia among Francisella spp. according to its complete 16S rDNA, 16S-23S intergenic spacer, 23S rDNA, 23S-5S intergenic spacer, 5S rDNA, FopA, lipoprotein TUL4 (LpnA), malate dehydrogenase and hypothetical lipoprotein (LpnB) sequences. A comparison between GM2212 and the type strain of Francisella philomiragia were performed by DNA-DNA hybridization and fatty acid analysis. The DNA-DNA hybridization showed a 70% similarity. The fatty acid analysis showed only minor differences between the Francisella isolates. Due to the inconclusive result from the DNA-DNA hybridisation, major emphasis concerning the status of this isolate is made on previously published molecular, phenotypic and biochemical characters. All characteristics taken together support the establishment of GM2212 as a novel species, for which the name Francisella piscicida sp. nov. is proposed (=CNCM I-3511(T) = DSM 18777(T) = LMG registration number not yet available).

Vibrio anguitlarum isolates were sampled from cod fry showing clinieal signs of vibriosis at different cod farms along the western eoast of Norway. Exeept for one isolate, all were shown to cause mortality in laboratory challenge experiments. Using biochemical analysis and specific rabbit antisera (Ol-O5), all the pathogenic isolates were classified as typical V. anguitlarum serotype O2. SDS-PAGE and Western blot analysis of both whole bacterial cells and purified lipopolysaccharides (LPS) showed that the LPS struetures were heterogeneous. ELISA analyses using adsorbed antisera identified the presence of two different subgroups within serogroup O2, which correspond with O2a/O2a' and O2b/O2jS described previously.