Phenotypic, serological and genetic characterization of Flavobacterium psychrophilum strains isolated from salmonids in Chile

Abstract

Characterization of 20 Flavobacterium psychrophilum strains isolated from farmed Atlantic salmon and rainbow trout in Chile was done using phenotypic, antigenic and genetic techniques. Experimental infections were also performed to assess the virulence of two representative isolates and of the type strain. Biochemical and physiological analyses showed that Chilean F. psychrophilum strains, regardless of the host species, constitute a phenotypically very homogeneous group matching with previous descriptions of this pathogen. However, serological assays indicated the existence of antigenic heterogeneity with four patterns of serological reactions. The first group contained most (14 of 20) of the F. psychrophilum isolates showing cross-reaction with the antisera obtained against Atlantic salmon and rainbow trout isolates. Group 2 corresponded to four other rainbow trout isolates (1658, 1731, 1762 and 29009) that did not agglutinate with anti-1150 serum. Two minor serological groups were identified for the remaining isolates (Groups 3 and 4). Marked homogeneity was also revealed by genetic studies including 16S rRNA alleles, random amplified polymorphic DNA and REP-PCR showing that a major genetic group of F. psychrophilum may be dominant in disease outbreaks in farms. Restriction fragment length polymorphism of PCR analysis showed that gyrase genotypes B-S or B-R were found in Chilean isolates from rainbow trout and Atlantic salmon, whereas genotype A was not found. Virulence assays using Atlantic salmon indicated no relationship between the degree of pathogenicity and the host origin of the F. psychrophilum strains.

Phase variation in Flavobacterium psychrophilum: characterization of two distinct colony phenotypes

“…The variability in the number of O-polysaccharide chain repeating units could be linked to the difference in the serotypes of the rough variants, as these structures have been used for serotyping F. psychrophilum . The LPSs of both the smooth and rough cells of F. psychrophilum were found to be smooth, which is in accordance with previous studies , Valdebenito & Avendaño-Herrera 2009. Since no distinct differences in total protein, OMP and LPS banding patterns were found between the smooth and rough cells, the possible differences in surface structures are probably located somewhere else, e.g.…”

“…The whole cell protein and OMP banding pattern of the caseinase negative and non-motile rough variant P6-3R/07 was also clearly different from the banding patterns of the other isolates, but further investigations are needed to explain these differences. The OMP banding patterns of the isolates in the present study were quite similar overall to the OMP banding patterns of Danish and Chilean Flavobacterium psychrophilum isolates (Møller et al 2005, Valdebenito & Avendaño-Herrera 2009. The LPS profiles did not reveal any differences between the smooth and rough cells either; only variability between isolates was found.…”

“…Holt 1987, Bertolini et al 1994, Lorenzen & Olesen 1997, Crump et al 2001, Valdebenito & Avendaño-Herrera 2009, and several of the characteristics have, in many studies, been identical between isolates. However, some differences in biochemical characteristics (Bertolini et al 1994), cell surface appearance, whole cell proteins (Holt 1987), association with rainbow trout Oncorhynchus mykiss phagocytes (Wiklund & Dalsgaard 2003), hydrophobicity and hemagglutination (Møller et al 2003) have been found between F. psychrophilum isolates.…”

Investigation of the presence and antibiotic susceptibilities of Flavobacterium psychrophilum in rainbow trout farms (Oncorhynchus mykiss Walbaum, 1792) in The Middle and Eastern Black Sea Regions of

“…In this study, also it was observed that all five isolates showed high level of homogeneity in their biochemical and morphological characteristics. Moreover, the phenotypic characteristics of these strains were similar to those identified in previous studies (21,23,34).…”

Bacteriophage Resistance Mechanisms in the Fish Pathogen Flavobacterium psychrophilum: Linking Genomic Mutations to Changes in Bacterial Virulence Factors

“…The pathogen occurs frequently in salmonid production sites and has been a problem in aquaculture worldwide since the first isolation in Washington, USA (1). Genetic characterization of F. psychrophilum strains has shown a low level of diversity with a distinct association of specific strains with particular fish species (2,3). The complete genome sequence of the virulent F. psychrophilum strain JIPO2/86 (ATCC 49511) revealed a 2,861,988-bp circular chromosome with 2,432 predicted protein-coding genes.…”