In 7 instances between 2000 and 2003, clinical investigation of populations of fresh-and seawater-reared, vaccinated, Atlantic salmon Salmo salar suffering total losses of between 0.1 and 35% revealed infection with a Gram-positive rod-shaped bacterium. The isolations were geographically widespread, occurring in both Norway and Scotland. In all cases, a Gram-positive bacterium, subsequently identified as Rhodococcus erythropolis, was isolated in pure culture. Infections, although systemic, were focused within the peritoneal cavity. While initial attempts to reproduce the disease by intraperitoneal injection of unvaccinated Atlantic salmon failed, Koch's postulates were subsequently fulfilled in fish vaccinated with a commercially available oil-adjuvanted vaccine. MATERIALS AND METHODS Fish.Moribund fish from all 7 disease outbreaks (see Table 1) were sampled for pathological and bacteriological examination.Histopathology. Gills, heart, liver, kidney, spleen, pancreatic tissue, skeletal musculature and occasionally brain were sampled for histopathology. The samples were fixed in 4% neutral buffered formalin, embedded in paraffin wax and routinely processed. The sections were stained by haematoxylin and eosin (H&E). A selected number of slides were also stained using Gram and May Grünwald Giemsa stains.Bacteriology. For bacteriological examination, samples from kidney and in some cases ascitic fluid, were inoculated onto blood agar (BA, 4% bovine or equine blood ) and blood agar supplemented with 1.5% NaCl (BAS) followed by aerobic incubation at 22 and 15°C, respectively. Plates were observed for 7 d. Bacterial isolates were subsequently stored at -80°C.Biochemical characterisation. Basic biochemical characterisation was performed using standard methods. Each strain was also tested using BIOLOG (Hayward) and API 20 NE (Biomerieux) kits according to the manufacturers' instructions. The ability of each strain to assimilate various carbon sources was examined by inoculating API 50 CH kits (Biomerieux) with bacteria suspended in a medium comprising 1.5 g agar, 2.0 g ammonium sulphate, 0.25 g Casamino acids (Difco) and 1 ml trace element solution.DNA sequencing. The 16S rRNA gene of Strains 00/50/6670 and 4115 were amplified using PCR and primers FD1 and RP2 (Weisburg et al. 1991). DNA sequencing was performed using the BigDye™ terminator cycle sequencing ready reaction kit (PE Applied Biosystems) and an automatic ABI prism 377 sequencer (Perkin Elmer). Sequence analysis was performed using the sequencer program (Gene Codes) and BLAST search analysis (Altschul et al. 1997).Phylogenetic analysis. Sequences were aligned using CLUSTAL W (Thompson et al. 1994). A neighbour-joining tree based on Kimura 2-parameter distances was calculated using PAUP* 4.0 (Swofford 2000). The tree was bootstrapped 1000 times to assess node reliability.Enterobacterial repetitive intergenic consensus PCR (ERIC-PCR). ERIC-PCR was performed using the forward primer 5'-atg taa gct cct ggg gat tca c-3' and reverse primer 5'-aag taa gtg...

MIC testing of Vibrio anguillarum isolates recovered from diseased farmed Atlantic cod revealed oxolinic acid MICs of ≤0.001, 0.06, and 16 μg ml−1. Single gyrA Ser-Ile substitutions were identified at position 83 of the intermediate and resistant strains, while a parC Ser-Leu substitution at position 85 was found only in the resistant strain.