Clonal relationships between invasive and noninvasive Lancefield group C and G streptococci and emm-specific differences in invasiveness.

Lancefield group G and group C streptococci (GGS and GCS, respectively) are pathogens responsible for a number of life-threatening infections. A collection of 116 recent (1998 to 2004) invasive (n = 28) and noninvasive (n = 88) GGS and GCS clinical isolates from Portugal were characterized. All isolates were identified as Streptococcus dysgalactiae subsp. equisimilis and characterized by emm typing and DNA macrorestriction profiling using pulsed-field gel electrophoresis (PFGE). emm typing revealed the presence of 22 distinct types, including 3 novel types. PFGE identified 14 clones with more than two isolates, but over half of the isolates were concentrated in 3 large clones. Individual clones and emm types showed a low level of association, since the majority of the clones included more than one emm type and the same emm type was found among diverse genetic backgrounds. Two emm types, stg2078 and stg10, were significantly more frequent among invasive isolates, and another two, stg6792 and stg166b, were present only in noninvasive isolates, suggesting a correlation between emm type and invasive disease potential.