The aim of the study was to evaluate biochemical features of 575 Polish isolates of S. suis from pigs with symptoms of streptococcosis and to improve methods of identification of the pathogen. The following tests were used to evaluate biochemical features of the strains: raffinose, inulin, mannitol, arginine and esculin fermentation, and production of acetoin, β-glucuronidase as well as amylase (on starch agar plates). Typical reactions were observed in 538 isolates (94%). The highest number of positive results was obtained in the β-glucuronidase production test in which 100% of the isolates demonstrate activity of mentioned enzyme. Since positive results were evidenced in 563 isolates (98%), raffinose fermentation was also a specific feature of the tested isolates. Less specific (93% of positive strains) results were proved for the following tests: acetoin and amylase production as well as inulin fermentation. Arginine dihydrolase activity was demonstrated in 523 tested isolates (91%) and 69% had the ability to hydrolyze esculin. The least specific result was obtained in the mannitol fermentation test: 33% of the typical reactions. 14 biochemical profiles were estimated among the analyzed isolates. 60% of the strains were classified in groups B and H. In group H only the strains with typical for S. suis pattern, reaching 22.3% of the tested isolates, were placed. This study confirmed S. suis to be highly heterogenous in biochemical profiles. In our opinion the evaluation of biochemical features is not a universal method and should not be considered as a basis for bacterial identification. This method can be used as an additional test for S. suis identification, supplemented by other, more reliable techniques.
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