Streptococcus dysgalactiae

Streptococcus dysgalactiae is a gram positive, beta-haemolytic, coccal bacterium belonging to the family Streptococcaceae. It is capable of infecting both humans and animals, but is most frequently encountered as a commensal of the alimentary tract, genital tract, or less commonly, as a part of the skin flora. The clinical manifestations in human disease range from superficial skin-infections and tonsillitis, to severe necrotising fasciitis and bacteraemia. The incidence of invasive disease has been reported to be rising. Several different animal species are susceptible to infection by S. dysgalactiae, but bovine mastitis and infectious arthritis in lambs (joint ill) have been most frequently reported.

Streptococcus dysgalactiae is currently divided into the subspecies Streptococcus dysgalactiae subsp. equisimilis and Streptococcus dysgalactiae subsp. dysgalactiae; the former mostly associated with human disease, and the latter almost exclusively encountered in veterinary medicine. Their exact taxonomic delineation, however, is a matter of ongoing debate (See taxonomy).

The names are derived from Greek; Streptococcus meaning chain forming (Streptos) rounded berry-like bodies (kokkos), referring to their usual appearance under a light-microscope. Dys (bad) galactiae (milk) alludes to their propensity to cause bovine mastitis. Equi (horse) similis (like) infers similarity to the closely related species, Streptococcus equi.