Identification of isolates of Streptococcus canis infecting humans

During a survey of Group G and C streptococcal infections of humans two epi demiologically unrelated Group G streptococcal isolates were identified, on e from a case of bacteremia and one from a wound infection. These isolates were atypical among this sample in that the emm gene could not be amplified from them by PCR. Biochemical characterization identified the isolates as Streptococcus canis, an organism normally associated with animal hosts. The biochemical identification was confirmed by sequencing of the 16S rRNA gen e from both isolates and comparison with sequences of the S. canis type str ain and other related streptococci of animals and humans. Comparative seque ncing of fragments of two other housekeeping genes, sodA and mutS, confirme d that the isolates are most closely related to S. canis. The identificatio n of two isolates of S. canis from a relatively small sample set suggests t hat the practice of identifying streptococci only by the Lancefield serolog ical group may result in underestimation of the presence of S. canis in the human population.