Four closely related species, Vibrio fischeri, Vibrio logei, Vibrio salmonicida and Vibrio wodanis, form a clade within the family Vibrionaceae; the taxonomic status and phylogenetic position of this clade have remained ambiguous for many years. To resolve this ambiguity, we tested these species against other species of the Vibrionaceae for phylogenetic and phenotypic differences. Sequence identities for the 16S rRNA gene were ≥97.4 % among members of the V. fischeri group, but were ≤95.5 % for members of this group in comparison with type species of other genera of the Vibrionaceae (i.e. Photobacterium and Vibrio, with which they overlap in G+C content, and Enterovibrio, Grimontia and Salinivibrio, with which they do not overlap in G+C content). Combined analysis of the recA, rpoA, pyrH, gyrB and 16S rRNA gene sequences revealed that the species of the V. fischeri group form a tightly clustered clade, distinct from these other genera. Furthermore, phenotypic traits differentiated the V. fischeri group from other genera of the Vibrionaceae, and a panel of 13 biochemical tests discriminated members of the V. fischeri group from type strains of Photobacterium and Vibrio. These results indicate that the four species of the V. fischeri group represent a lineage within the Vibrionaceae that is distinct from other genera. We therefore propose their reclassification in a new genus, Aliivibrio gen. nov. Aliivibrio is composed of four species: Aliivibrio fischeri comb. nov. (the type species) (type strain ATCC 7744T =CAIM 329T =CCUG 13450T =CIP 103206T =DSM 507T =LMG 4414T =NCIMB 1281T), Aliivibrio logei comb. nov. (type strain ATCC 29985T =CCUG 20283T =CIP 104991T =NCIMB 2252T), Aliivibrio salmonicida comb. nov. (type strain ATCC 43839T =CIP 103166T =LMG 14010T =NCIMB 2262T) and Aliivibrio wodanis comb. nov. (type strain ATCC BAA-104T =NCIMB 13582T =LMG 24053T).

Studies were conducted to determine the cause of outbreaks of luminous vibriosis in phyllosoma larvae of the packhorse rock lobster Jasus verreauxi reared in an experimental culture facility. On 2 separate occasions mortalities of up to 75% over a period of 4 wk were observed in 4th to 5th and 8th to 10th instar phyllosomas at water temperatures of 20 and 23°C, respectively. Affected larvae became opaque, exhibited small red spots throughout the body and pereiopods, and were faintly luminous when viewed in the dark. Histopathology showed that the gut and hepatopancreas tubules of moribund phyllosomas contained massive bacterial plaques. The hepatopancreas tubules of moribund larvae were atrophic and some contained necrotic cells sloughed into the lumen. Dense, pure cultures of a bacterium identified as Vibrio harveyi were isolated from moribund larvae. The disease syndrome was reproduced by in vivo challenge and V. harveyi was successfully reisolated from diseased larvae after apparently healthy larvae were exposed by immersion to baths of more than 10 4 V. harveyi ml -1 at 24°C. Injured larvae were more susceptible to infection than were healthy larvae. Survival of larvae experimentally and naturally exposed to V. harveyi was improved when antibiotics were administered via bath exposures.

Yersinia ruckeri is a salmonid pathogen with widespread distribution in cool-temperate waters including Australia and New Zealand, two isolated environments with recently developed salmonid farming industries. Phylogenetic comparison of 58 isolates from Australia, New Zealand, USA, Chile, Finland and China based on non-recombinant core genome SNPs revealed multiple deep-branching lineages, with a most recent common ancestor estimated at 18 500 years BP (12 355–24 757 95% HPD) and evidence of Australasian endemism. Evolution within the Tasmanian Atlantic salmon serotype O1b lineage has been slow, with 63 SNPs describing the variance over 27 years. Isolates from the prevailing lineage are poorly/non-motile compared to a lineage pre-vaccination, introduced in 1997, which is highly motile but has not been isolated since from epizootics. A non-motile phenotype has arisen independently in Tasmania compared to Europe and USA through a frameshift in fliI, encoding the ATPase of the flagella cluster. We report for the first time lipopolysaccharide O-antigen serotype O2 isolates in Tasmania. This phenotype results from deletion of the O-antigen cluster and consequent loss of high-molecular-weight O-antigen. This phenomenon has occurred independently on three occasions on three continents (Australasia, North America and Asia) as O2 isolates from the USA, China and Tasmania share the O-antigen deletion but occupy distant lineages. Despite the European and North American origins of the Australasian salmonid stocks, the lineages of Y. ruckeri in Australia and New Zealand are distinct from those of the northern hemisphere, suggesting they are pre-existing ancient strains that have emerged and evolved with the introduction of susceptible hosts following European colonization.

An experimentally induced bacterial infection of marine Atlantic salmon Salmo salar smolt gills was developed using strains of Tenacibaculum maritimum originally isolated from disease outbreaks in Tasmania. The gills of salmon were inoculated with a high concentration of bacteria (4 × 10 11 cells per fish) of either strain 00/3280 or 89/4747 T. maritimum. Gentle abrasion of the gills was used to enhance the progression of gill disease. One strain (00/3280) was highly pathogenic, causing morbidity and mortality within 24 h post-inoculation, and produced acute focal branchial necrosis associated with significant increases in plasma osmolality and lactate concentration compared with controls (non-inoculated) or strain 89/4747-inoculated fish. There were no differences in the whole body net ammonium flux between control (non-inoculated) and strain 00/3820-inoculated fish. Gill abrasion resulted in acute telangiectasis and focal lamellar hyperplasia in all fish regardless of bacterial inoculation. This work provides the basis of a challenge model suitable for investigating the pathophysiological processes associated with acute branchial necrosis in marine fish, suggesting that osmoregulatory and possibly respiratory dysfunction are the primary consequences of infection. KEY WORDS: Atlantic salmon · Tenacibaculum maritimum · Pathophysiology · Gill disease · Osmoregulation · Respiration Resale or republication not permitted without written consent of the publisherDis Aquat Org 61: [179][180][181][182][183][184][185] 2004 MATERIALS AND METHODS Preparation of bacterial cultures. Cultures ofTenacibaculum maritimum were isolated by the Department of Primary Industry, Water and Environment from the skin of farmed salmon from Tasmania, Australia, with clinical cases of cutaneous erosion disease. The cultures were designated 89/4747 (Atlantic salmon) and 00/3280 (rainbow trout) and were isolated in 1989 and 2000 respectively. The bacteria were isolated on the medium of Anacker & Ordal (1959), formulated with seawater. Isolates were identified using a 16S ribosomal RNA (rRNA) PCR primer set specific for T. maritimum (Carson 1998). Cultures were stored frozen at -80°C on MicroBank beads (Pro-Lab Diagnostics) until required.Cultures for infection trials were prepared by inoculating 200 ml of Shieh's medium (Song et al. 1988) formulated with seawater (mineral salts buffer, MSB) in a 1 l conical flask and incubated with gentle agitation (30 cycles min -1 ) at 20 to 22°C for 48 h. The cell suspension was harvested by centrifugation at 2500 µg RCF (relative centrifugal force) for 20 min and the pellet washed twice with sterile seawater. Harvested cells were resuspended in 15 ml of sterile seawater.Experimental series 1: Infection study. Atlantic salmon smolts of mean mass (± SE) 77.0 ± 2.9 g were acclimated to full strength seawater (35 ppt) over a period of 10 d, then allocated to triplicate tanks (4 fish per tank, n = 12 per treatment) and allowed to habituate for 24 h prior to anaesthetization with AQUI-S (0.04 ml l...

This comprehensive population study substantially improves our understanding of the epizootiological history and nature of an internationally important fish-pathogenic bacterium. The MLVA assay developed and presented represents a high-resolution typing tool particularly well suited for Yersinia ruckeri infection tracing, selection of strains for vaccine inclusion, and risk assessment. The ability of the assay to separate isolates into geographically linked and/or possibly host-specific clusters reflects its potential utility for maintenance of national biosecurity. The MLVA is internationally applicable and robust, and it provides clear, unambiguous, and easily interpreted results. Typing is reasonably inexpensive, with a moderate technological requirement, and may be completed from a harvested colony within a single working day. As the resulting MLVA profiles are readily portable, any Y. ruckeri strain may rapidly be placed in a global epizootiological context.