Background
An increasing incidence of Streptococcus dysgalactiae subspecies equisimilis (SDSE) human infections has been reported together with substantial genetic diversity and geographical variation in the prevalence of SDSE lineages. The current study aimed at exploring potential differences in disease presentation of SDSE lineages causing human infections in Portugal.
Methods
From 2011 to 2018, 1458 SDSE isolates were recovered from invasive (n=379) and non-invasive (n=1079) infections. Lancefield group and emm type were determined for all isolates. High throughput sequencing (Illumina) was performed for representative isolates and seven-gene multilocus (MLST) sequence type (ST) was extracted from genomic data. MLST clonal complexes (CCs) were defined by goeBURST using all data available at PubMLST.
Results
SDSE isolates belonged to Lancefield groups G (n=1030), C (n=423), A (n=4) or L (n=1). Among the 43 emm types found, stG62647 was the most frequent (n=347, 23.4%) and included mostly group C isolates (n=300). emm type stC74a was overrepresented among invasive infections, stG166b in skin and soft tissue infections and stC36 and stC839 among respiratory tract infections (all p<0.01). While stC74a and stG166b isolates were mainly associated with CCs with worldwide distribution (including the highly prevalent CC17 and CC29), stC36 (mainly CC49 and CC68, represented by STs uncommon elsewhere) and stC839 (CC3) were associated with infrequent CCs.
Conclusions
SDSE isolates causing human infections in Portugal are genetically diverse. This study highlighted differences in propensity to cause particular infections between SDSE lineages.