Morphological and biochemical differences among isolates of Yersinia ruckeri obtained from wide geographical areas

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Abstract
The morphological and biochemical characteristics of 147 strains of Yersinia ruckeri obtained from Australia, South Africa, North America and Europe were compared. The majority of strains could be divided into coccobacillary organisms or medium sized rods, but this morphological diversity was not correlated with any particular biochemical characteristic. Overall, 18% of strains were non‐motile but this was geographically biased in that 23 out of 26 non‐motile strains were isolated in the UK. Gelatin and casein hydrolysis, acetoin production, sorbitol fermentation and Tween hydrolysis were the most variable biochemical reactions. Tween hydrolysis reactions differed from the other variable characteristics in that, with the exception of a single motile reference strain, all Tween hydrolysis negative strains were non‐motile and vice versa. It is suggested that non‐motile, Tween hydrolysis negative strains be recognised as Y. ruckeri biotype 2.