Identification of Yersinia ruckeri from diseased salmonid fish by Fourier transform infrared spectroscopy

Yersinia ruckeri is the causative agent of enteric redmouth disease (ERM), which mainly affects salmonid fish. Isolates of Y. ruckeri from diseased salmonid fish were obtained over a 6‐year period from eight fish farms in the State of Baden‐Württemberg, Southwest Germany. The strains were characterized by biochemical methods and Fourier transform infrared spectroscopy (FT‐IR) combined with artificial neural network analysis. These methods were complemented by 16S rDNA sequencing for several isolates. The set of strains from these fish farms included sorbitol‐positive, gelatinase‐positive and non‐motile Y. ruckeri. These variants were differentiated with an advanced FT‐IR module, which is part of a higher‐ranking method including more than 200 well‐defined Yersinia strains against a background of more than 1000 other Gram‐negative isolates. Validation of the newly constructed method yielded 97.4% of Y. ruckeri identified correctly on the species level. Thus, the FT‐IR analysis enables distinction of all Y. ruckeri from other Yersinia species (e.g. fish‐borne Y. enterocolitica) and other Enterobacteriaceae typically misidentified because of similar biochemical reaction profiles, especially Hafnia alvei. The differentiation of sorbitol‐positive variants of Y. ruckeri using FT‐IR was demonstrated.