Phenotypical and genetic characterization of Yersinia ruckeri strains isolated from recent outbreaks in farmed rainbow trout Oncorhynchus mykiss (Walbaum) in Peru

A total of 30 strains of Yersinia ruckeri causing recent outbreaks in Peruvian trout culture systems, were studied by means of biochemical characteristics, serology, lipopolysaccharide (LPS) and outer membrane protein (OMP) analysis, and ERIC and REP PCR fingerprinting. All the Peruvian isolates were found to be fermentative, oxidase negative and positive for decarboxylation of lysine and ornithine and utilization of glucose and mannitol, allowing their presumptive identification as Y. ruckeri. Sequencing of the 16S rRNA gene confirmed that isolates were indeed Y. ruckeri (> 99.98% identity). Although most of the strains studied were motile and lipase positive corresponding to the biotype 1 of Y. ruckeri, 5 of these strains were negative from both tests, being identified as biotype 2. In addition, drug susceptibility tests determined high sensitivity to sulfamethoxazole/trimethoprim, oxytetracycline, ampicillin and enrofloxacin in all the isolates. Serologically, all the Peruvian strains studied were identified as belonging to the serotype O1 subgroup a. Analysis of the lipopolysaccharide (LPS) as well as total and outer membrane proteins (OMPs) profiles and the correspondent inmunoblotting, supported these results. Genotyping performed by means of ERIC- and REP-PCR determined major correlation of the Peruvian isolates with the type strain NCIMB 2194T regardless of the biotype.