We report here the complete genome sequence of the virulent strain JIP02/86 (ATCC 49511) of Flavobacterium psychrophilum, a widely distributed pathogen of wild and cultured salmonid fish. The genome consists of a 2,861,988-base pair (bp) circular chromosome with 2,432 predicted protein-coding genes. Among these predicted proteins, stress response mediators, gliding motility proteins, adhesins and many putative secreted proteases are probably involved in colonization, invasion and destruction of the host tissues. The genome sequence provides the basis for explaining the relationships of the pathogen to the host and opens new perspectives for the development of more efficient disease control strategies. It also allows for a better understanding of the physiology and evolution of a significant representative of the family Flavobacteriaceae, whose members are associated with an interesting diversity of lifestyles and habitats.
Members of most Chryseobacterium species occur in aquatic environments or food products, while strains of some other species are pathogenic to humans and animals. A collection of 52 Chryseobacterium sp. strains isolated from diseased fish, one frog isolate and 22 reference strains were included in a polyphasic taxonomy study. Fourteen clusters of strains were delineated following the comparison of whole-cell protein profiles. Most of these clusters were confirmed when the phenotypic and RAPD profiles and the 16S rRNA gene sequences were compared. Fatty acid composition helped differentiate the Chryseobacterium strains from members of related genera. None of the fish isolates could be allocated to the two species previously reported from fish but two isolates belonged to C. joostei, while the frog isolate was identified as Elizabethkingia meningoseptica, a human pathogen previously included in the genus Chryseobacterium. Three clusters grouping from 3 to 13 isolates will probably constitute the core of new Chryseobacterium species but all other isolates occupied separate or uncertain positions in the genus. This study further demonstrated the overall high similarity displayed by most Chryseobacterium strains whatever the technique used and the resulting difficulty in delineating new species in the genus. Members of this bacterial group should be considered potential emergent pathogens in various fish and frog species, farming conditions and geographical areas.
Following severe outbreaks of a disease with dermal necrosis, several bacterial strains were isolated from sea bass (Dicentrarchus labrax) reared on French coasts. A phenotypic study revealed that the isolates closely resembled Flexibacter maritimus. Nine selected strains were compared to 8 F. maritimus reference strains from other geographical origins and to the type strain NCIMB 2154T. DNA base composition of the strains tested was in the G + C range of 30.6 to 32 mol%. A study on the DNA relatedness among the strains by the S1 nuclease DNA-DNA hybridization method showed that the 12 strains tested formed a tight genomic species with DNA homologies above 74%. The profiles obtained from API ZYM galleries, polyacrylamide gel electrophoresis of whole-cell proteins, and fatty acids analysis revealed that F. maritimus is a very homogeneous bacterial species. This is the first identification of this fish pathogen in France and its first isolation from sea bass.
Aim: To investigate the distribution of antimicrobial resistance to phenicols in the fish pathogenic bacteria Aeromonas salmonicida, motile Aeromonas, Yersinia ruckeri, lactic bacteria and the nutritionally fastidious Flavobacterium psychrophilum. The last species was screened on two media (diluted Mueller-Hinton and peptoneenriched Anacker and Ordal), both supplemented with horse serum. Methods and Results: Minimal inhibitory concentration (MIC) assessment, using the agar dilution method according to proposed standards, confirmed that chloramphenicol resistance was more frequent and expressed at higher levels than florfenicol resistance. A significant resistant population, highlighted by the bimodal distribution of MICs, was detected only for chloramphenicol in A. salmonicida. No link could be found with the geographical origin of the isolates or fish species. Other cases of resistance appeared randomly distributed or related to the natural properties of the bacterial species. Although the two media used for testing F. psychrophilum resulted in comparable performances in dilution methods, Anacker and Ordal was more adapted to disc diffusion tests. Conclusion: Despite wide use, resistance to florfenicol does not seem to occur frequently in French fish farms. Significance and Impact of the Study: It is important to maintain a surveillance, as development of florfenicol resistance has occasionally been documented. For this purpose, and for the species studied in this work, the recently proposed standards appear generally well-adapted.
Five strains of gliding bacteria were isolated in France from farmed diseased rainbow trouts reared at low water temperature. The resemblance of these bacteria to the known fish pathogen "Cytophaga psychrophila" led to their comparative study with reference strain NCMB 1947 and with an American isolate. Morphological, physiological, and biochemical characteristics of the seven strains proved to be similar. Comparison of their DNA by the S1 nuclease DNA-DNA hybridization method showed that the seven strains formed a tight genomic species with DNA relatedness above 90%. This is the first identification of this fish pathogen in a European country. The main phenotypic characteristics differentiating this bacterium from other nonpathogenic gliding bacteria of fish origin include a poor gliding movement, yellow compact or weakly rhizoid colonies on solid media, and the presence of flexirubin-type pigments. The inability to metabolize any carbohydrates, the strong proteolytic activity, the absence of growth in more than 0.5% NaCl, and the tolerance to a maximum temperature of 25°C are also useful characteristics of this group of bacteria.
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