Abstract

Two unidentified Gram-positive, catalase-negative, coccus-shaped organisms were recovered from pigs and subjected to a polyphasic taxonomic analysis. Based on cellular morphology and biochemical criteria, the isolates were tentatively assigned to the genus Streptococcus, although the organisms did not appear to correspond to any recognized species. Comparative 16S rRNA gene sequence studies confirmed this identification and showed that the nearest phylogenetic relatives of the unknown cocci were Streptococcus plurextorum 1956-02(T) and Streptococcus suis NCTC 10234(T) (97.9 and 96.0 % 16S rRNA gene sequence similarity, respectively). The new isolates were related most closely to S. suis CIP 103217(T) based on rpoB gene sequence analysis (<8 % sequence divergence). DNA-DNA pairing studies showed that one of the unidentified strains (2923-03(T)) displayed DNA relatedness values of 26.6 and 27.2 % with S. plurextorum CECT 7308(T) and S. suis NCTC 10234(T), respectively. On the basis of phenotypic and phylogenetic evidence, it is proposed that the unknown isolates from pigs be classified in the genus Streptococcus as members of Streptococcus porci sp. nov., with the type strain 2923-03(T) (=CECT 7374(T) =CCUG 55896(T)).