Differentiation of human and animal strains of Streptococcus dysgalactiae by pulsed-field gel electrophoresis

The genetic diversity among 54 human isolates and 33 animal isolates belonging to the species Streptococcus dysgalactiae (20 alpha-haemolytic Streptococcus dysgalactiae, 23 Streptococcus equisimilis, 43 group G streptococci and one group L streptococcus) was evaluated by macrorestriction analysis of chromosomal DNA with SmaI and resolution by pulsed-field gel electrophoresis. This technique revealed a high degree of intraspecies polymorphism, leading to the differentiation of 80 distinct banding patterns, and identified the presence of two major clusters, one containing isolates of human origin and the other isolates of animal origin. These results suggest that human and animal isolates of S. dysgalactiae are genetically distinct, and support the recent proposal of the subspecies S. dysgalactiae subsp. equisimilis for human isolates. The heterogeneity revealed within isolates from the same host type indicates that pulsed-field gel electrophoresis is a powerful epidemiological tool for studying S. dysgalactiae infections.