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United States Department of Agriculture

Agricultural Research Service

Title: Starch Hydrolysis Testing of Multiple Isolates for Rapid Differentiation of Streptococcus Iniae

Authors
item Evans, Joyce
item Klesius, Phillip
item Shoemaker, Craig

Submitted to: European Association of Fish Pathologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 13, 2004
Publication Date: October 1, 2004
Citation: Evans, J.J., Klesius, P.H., Shoemaker, C.A. 2004. Starch hydrolysis testing of multiple isolates for rapid differentiation of streptococcus iniae. Bulletin of the European Association of Fish Pathologists. 24(5)2004:231-239.

Interpretive Summary: The starch hydrolysis test is used to aid in species differentiation among various disease causing bacteria in fish. Streptococcus iniae is one of the few Streptococcus organisms producing starch hydrolysis. This test is essential for its identification and for the differentiation of the streptococcal species causing fish disease outbreaks. We evaluated 10 pathogenic streptococcal isolates, Streptococcus iniae, S. agalactiae and Enterococcus spp., for their ability to hydrolyze starch on a single starch agar plate following 18 h incubation. Only S. iniae hydrolyzed starch. This method maximizes the number of isolates tested and minimizes supplies needed and time required for results. We have improved this method to increase the number of isolates that can be tested at once for rapid and cost effective results. Furthermore, these results indicate that starch hydrolysis may be quantified by this method.

Technical Abstract: We evaluated 10 pathogenic streptococcal isolates, Streptococcus iniae, S. agalactiae, and Enterococcus spp. API 20 and CH 50 for their ability to hydrolyze starch on a single starch agar plate in replicate following 18 h incubation at 35°C. Twenty- eight additional S. iniae isolates from different geographical regions and fish species were also evaluated by this method. This starch hydrolysis technique maximizes the number of isolates tested and minimizes supplies needed and time required for results. In another experiment, we evaluated starch reactions (hydrolysis by this method and starch acidification using API 20 and CH 50 multi-test systems) of related streptococcal species and compared these results to what has been reported for these species. Only S. iniae hydrolyzed starch. Starch acidification of S. iniae was noted in API 20 and CH 50 assays. Starch acidification of S. iniae from multi-test systems should not be interpreted as starch hydrolysis.

Last Modified: 4/16/2014
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