Multilocus sequence analysis reveals different lineages of Pseudomonas anguilliseptica associated with disease in farmed lumpfish (Cyclopterus lumpus L.).

The bacterium Pseudomonas anguilliseptica has in recent years emerged as a serious threat to production of lumpfish in Norway. Little is known about the population structure of this bacterium despite its association with disease in a wide range of different fish species throughout the world. The phylogenetic relationships between 53 isolates, primarily derived from diseased lumpfish, but including a number of reference strains from diverse geographical origins and fish species, were reconstructed by Multi-Locus Sequence Analysis (MLSA) using nine housekeeping genes (rpoB, atpD, gyrB, rpoD, ileS, aroE, carA, glnS and recA). MLSA revealed a high degree of relatedness between the studied isolates, altough the seven genotypes identified formed three main phylogenetic lineages. While four genotypes were identified amongst Norwegian lumpfish isolates, a single genotype dominated, irrespective of geographic origin. This suggests the existence of a dominant genotype associated with disease in production of lumpfish in Norwegian aquaculture. Elucidation of the population structure of the bacterium has provided valuable information for potential future vaccine development.

DNA gyrase and topoisomerase IV mutations in quinolone-resistant Flavobacterium psychrophilum isolated from diseased salmonids in Norway.

Flavobacterium psychrophilum is the causative agent of the recognized diseases 'bacterial coldwater disease' and 'rainbow trout fry syndrome' and is found in many farmed freshwater and marine fish species. In Norway, the bacterium has mainly been isolated from Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.). In the present study, 26 isolates from Norwegian farmed salmonids were examined. All isolates were tested for susceptibility towards various antibacterial drugs by the disk diffusion method, and minimum inhibitory concentration values for oxolinic acid and flumequine were established for selected isolates. All isolates from rainbow trout displayed reduced susceptibility towards quinolones, while brown trout and Atlantic salmon isolates were susceptible. The quinolone resistance determining regions (QRDRs) of the gyrA, gyrB, parC, and parE genes were sequenced. Sequence analysis of the QRDR of gyrA in quinolone resistant isolates revealed a threonine:arginine amino acid substitution at position 82 in all 16 isolates from Norwegian rainbow trout and a single reference strain isolated from rainbow trout in Sweden. No evidence for plasmid-mediated quinolone resistance was found in any of the isolates. Pulsed-field gel electrophoresis and phylogenetic analysis of parC and gyrB sequences indicate a clonal relationship between rainbow trout isolates.

Flavobacterium psychrophilum associated with septicaemia and necrotic myositis in Atlantic salmon Salmo salar: a case report.

We describe the first case from Norway of increased mortality in Atlantic salmon Salmo salar (L.), with septicaemia and necrotic myositis, associated with infection by Flavobacterium psychrophilum. The outbreak occurred in smolt of 60 to 100 g in fresh water on a land-based farm in Western Norway during winter 2008-2009. The water temperature was < 5 degrees C and the accumulated mortality was 7.0%. Necropsy of dead and moribund fish revealed a swollen dark spleen, pale liver, serohaemorrhagic ascites and haemorrhage in the abdominal fat and muscle. F. psychrophilum was isolated from the kidney and spleen of diseased fish. Muscle biopsy revealed the presence of long filamentous rods in necrotic areas of skeletal muscle. Immunohistochemistry was positive for F. psychrophilum. Identification of cultured isolates as F. psychrophilum was confirmed using phenotypic testing and sequencing of the 16S rRNA gene. Analysis by allele-specific polymerase chain reaction (allele-specific PCR) indicated that 2 different genotypes of the bacterium were present in the outbreak.