Population Genetics of Streptococcus dysgalactiae Subspecies equisimilis Reveals Widely Dispersed Clones and Extensive Recombination

Abstract

Background Streptococcus dysgalactiae subspecies equisimilis (SDSE) is an emerging global pathogen that can colonize and infect humans. Although most SDSE isolates possess the Lancefield group G carbohydrate, a significant minority have the group C carbohydrate. Isolates are further sub-typed on the basis of differences within the emm gene. To gain a better understanding of their molecular epidemiology and evolutionary relationships, multilocus sequence typing (MLST) analysis was performed on SDSE isolates collected from Australia, Europe and North America.Methodology/Principal FindingsThe 178 SDSE isolates, representing 37 emm types, segregate into 80 distinct sequence types (STs) that form 17 clonal complexes (CCs). Eight STs recovered from all three continents account for >50% of the isolates. Thus, a small number of STs are highly prevalent and have a wide geographic distribution. Both ST and CC strongly correlate with group carbohydrate. In contrast, eleven STs were associated with >1 emm type, suggestive of recombinational replacements involving the emm gene; furthermore, 35% of the emm types are associated with genetically distant STs. Data also reveal a history of extensive inter- and intra-species recombination involving the housekeeping genes used for MLST. Sequence analysis of single locus variants identified through goeBURST indicates that genetic change mediated by recombination occurred ∼4.4 times more frequently than by point mutation.Conclusions/SignificanceA few genetic lineages with an intercontinental distribution dominate among SDSE causing infections in humans. The distinction between group C and G isolates reflects recent evolution, and no long-term genetic isolation between them was found. Lateral gene transfer and recombination involving housekeeping genes and the emm gene are important mechanisms driving genetic variability in the SDSE population.

Group C Streptococcus dysgalactiae subsp. equisimilis in south-east Brazil: genetic diversity, resistance profile and the first report of human and equine isolates belonging to the same multilocus sequence typing lineage

“…The DNA was extracted (Moore et al, 2004) and MLST was performed as described previously (Ahmad et al, 2009;McMillan et al, 2010). Further analyses included the construction of a global optimal eBURST diagram using goeBURST version 1.2.1 (http://goeburst.…”

Soft tissue infection caused by Streptococcus dysgalactiae subsp. equisimilis possessing group Aantigen: a and review of the literature

“…Usually SDSE strains have the group G antigen, more rarely the group C one. According to results of several large investigations (on more than 100 isolates), SDSE isolates with G antigen consisted from 70% to more than 90%, and those with C antigen -from 5% to 26% of the examined SDSE population [2][3][4][5][6][7][8]. The SDSE strains with group A and L antigens are isolated much less frequently [2, [9][10][11][12][13][14][15][16].…”

“…The SDSE strains with group A and L antigens are isolated much less frequently [2, [9][10][11][12][13][14][15][16]. In SDSE populations, the participation of strains with group A antigen may amount up to some 3.5% [2,17], and those with L antigen -up to 0.5% [4,6,8]. Group A antigen is carried by some strains of both SDSE and S. anginosus [18], which is why the term "group A streptococci" (GAS) should not be treated as synonymous to S. pyogenes.…”

“…About 50 emm types have been described in SDSE so far [6]. It has been observed that different emm types dominate in different geographical regions [19].…”

“…It has been observed that different emm types dominate in different geographical regions [19]. Several intercontinental clonal complexes of SDSE have been characterized [6].…”