First Report of Yersinia ruckeri Biotype 2 in the USA

Abstract

A polyphasic characterization of atypical isolates of Yersinia ruckeri (causative agent of enteric redmouth disease in trout) obtained from hatchery-reared brown trout Salmo trutta in South Carolina was performed. The Y. ruckeri isolates were biochemically and genetically distinct from reference cultures, including the type strain, but were unequivocally ascribed to the species Y. ruckeri, based on API 20E, VITEK, fatty acid methyl ester profiles, and 16S rRNA gene sequencing analysis. These isolates were nonmotile and unable to hydrolyze Tween 20/80 and were therefore classified as Y. ruckeri biotype 2. Genetic fingerprint typing of the isolates via enterobacterial repetitive intergenic consensus (amplified by polymerase chain reaction) and fragment length polymorphism showed biotype 2 as a homogeneous group distinguishable from other Y. ruckeri isolates. This is the first report of Y. ruckeri biotype 2 in the USA.

Yersinia ruckeri biotype 2 isolates from mainland Europe and the UK likely represent different clonal groups

“…There have been a series of recent reports of outbreaks of ERM caused by Yersinia ruckeri biotype 2 isolates (Austin et al 2003, Fouz et al 2006, Arias et al 2007). This study shows that the emergence and dissemination of these isolates is complicated.…”

“…ERM has been successfully controlled by vaccination with monovalent killed whole cell commercial vaccines, generally based on the Hagerman type strain (Horne & Barnes 1999). However, reports of ERM vaccine breakdown have emerged in Europe and the USA, which are attributed to biotype 2 (Tween 80-negative, nonmotile) isolates of Y. ruckeri (Austin et al 2003, Fouz et al 2006, Arias et al 2007. Biotype 2 isolates were first described as having caused the disease in UK rainbow trout by Davies & Frerichs (1989).…”

“…However, pulsotyping confirmed the earlier observations of Davies (1991a) that UK and European serotype O1 isolates causing ERM in rainbow trout formed distinct, non-overlapping subpopulations. These subpopulations had greater homology to US isolates than to each other, suggesting that Y. ruckeri was introduced separately into the UK and Europe from the USA and subsequent cross-border transfer of UK and European isolates has been limited.There have been a series of recent reports of outbreaks of ERM caused by Yersinia ruckeri biotype 2 isolates (Austin et al 2003, Fouz et al 2006, Arias et al 2007). This study shows that the emergence and dissemination of these isolates is complicated.…”

Serological and molecular heterogeneity among Yersinia ruckeri strains isolated from farmed Atlantic salmon Salmo salar in Chile

“…Although formulations of most commercial vaccines are based only on serovar I (Hagerman strain), different degrees of cross-protection among serotypes have been reported (Stevenson & Airdrie 1984). In recent years, reports of ERM vaccine breakdown have emerged in Europe and the USA, which were mostly attributed to biotype 2 strains (Austin et al 2003, Fouz et al 2006, Arias et al 2007, Wheeler et al 2009). …”

“…Outer membrane protein profiles of the strains studied. Lanes: 1, 1533 (O1b); 2, 8960; 3, 8526; 4, 9394; 5, 2550; 6, 8386; 7, 8958; 8, 11.29 (O2b); 9, 6807; 10, 11.4 (O1a) (Austin et al 2003, Fouz et al 2006, Arias et al 2007). Other cases (with lower incidence and mortality) were caused by strains of serotype O2b (Romalde et al 2003).…”