Yersinia ruckeri Biotypes 1 and 2 in France: presence and antibiotic susceptibility

Abstract

Yersinia ruckeri is the causative agent of yersiniosis, a disease reported in a number of fish species, especially rainbow trout. This study was undertaken to describe the phenotypes of Y. ruckeri on French rainbow trout farms. More than 100 isolates, collected during recent outbreaks on trout farms, were characterized by phenotypic tests, namely using biochemical tests of the API 20E system, serotyping, biotyping (tests for motility and lipase activity) and by describing the pattern of susceptibility to several antibiotics. The isolates showed a low phenotypic diversity with a prevalent serotype (O1) and API 20E profile 5 1(3)07 100. As in other European countries, Biotype 2 (BT2), which lacks both motility and secreted lipase activity, was found to be present in France. The emergence of 'French' BT2 was different than that observed for other European countries (Finland, Spain, Denmark and the UK). The antibiotic pattern was uniform for all isolates, regardless of the geographical area studied. The results indicate that no resistance has yet emerged, and the efficacy of the antibiotic generally used against yersiniosis in France, trimethoprim/sulfamethoxasol, is not compromised (minimum inhibitory concentrations [MIC] of between 0.016 and 0.128 µg ml-1). Enrofloxacin and doxycycline, not used as a first-line treatment in fish diseases, have reasonably good efficacies (with MICs ≤0.128 and 0.256, respectively).

Yersinia ruckeri Isolates Recovered from Diseased Atlantic Salmon (Salmo salar) in Scotland Are More Diverse than Those from Rainbow Trout (Oncorhynchus mykiss) and Represent Distinct Subpopulations

“…Although the number of rainbow trout isolates examined in the present study was smaller than that of Atlantic salmon isolates, they were isolated from widespread geographic regions over a 13-year period and are representative of the rainbow trout Y. ruckeri population in the United Kingdom. The observed homogeneity of rainbow trout isolates is also in agreement with various other recent studies (16,17,25,49). Greater sampling from rainbow trout may have revealed increased diversity, but the samples analyzed represented all isolates submitted for serotyping over the 13-year time period (probably reflecting the success of vaccination in rainbow trout).…”

“…In contrast to the majority of the isolates recovered from rainbow trout, the Atlantic salmon isolates were exclusively members of biotype 1. This observation suggests that the biotype 2 phenotype has not yet emerged in Scottish Atlantic salmon isolates as it has in European and North American rainbow trout isolates (16,17,(22)(23)(24)(25)(26)(27); however, it should be noted that the biotype 2 phenotype was previously described in a small number of older Atlantic salmon isolates originating from Norway (18) and the United Kingdom (24). The biotype 2 phenotype has arisen independently on at least four occasions within serotype O1 rainbow trout isolates in Europe and the United States by specific mutations in the genes (fliR, flhA, and flhB) involved in flagellar secretion; its distribution in Europe is not due simply to the expansion and distribution of a single clone (24,42).…”

“…It has long been recognized that serotype O1 isolates of Y. ruckeri have far greater prevalence in, and are more pathogenic toward, rainbow trout than are other serotypes; as pointed out above, it has been proposed that the epidemic expansion and dissemination of serotype O1 Y. ruckeri occurred when the pathogen found an alternative niche in intensively cultured rainbow trout (42). Conversely, non-O1 serotypes are usually associated with nonsalmonid species or with the environment, leading to the suggestion that different Y. ruckeri isolates exhibit various degrees of host specificity and virulence or adaptation for survival in the environment (16,31,63). Different pulsotypes and multilocus sequence types of Y. ruckeri are also associated with specific host species, strengthening the proposal for adaptive niche specialization (34,57).…”

“…The motile lipase-positive and nonmotile lipase-negative isolates were designated biotypes 1 and 2, respectively (22). Since the first identification of biotype 2 isolates in the United Kingdom, nonmotile variants have been described elsewhere in Europe (16,17,(23)(24)(25), the United States (26), and Australia (7). Indeed, biotype 2 Y. ruckeri strains are causing increasing concern because they are responsible for disease in fish previously vaccinated against biotype 1 strains (17,20,23,26,27).…”

“…Serotyping is particularly important for strain differentiation of Y. ruckeri, and the O-serotyping scheme of Davies (14) is the most commonly used (12,(15)(16)(17). In this scheme, five O serotypes, O1, O2, O5, O6, and O7, are recognized by rapid slide agglutination assay using defined O antigens (14); the individual O serotypes correspond to discrete lipopolysaccharide (LPS) types as identified by SDS-PAGE and Western blotting (18).…”