Abstract
Streptococcus dysgalactiae subsp. equisimilis (groups C and G streptococci [GCS/GGS]) is an increasingly recognized human pathogen, although it may follow indirect pathways. Prospective surveillance of selected households in 3 remote Aboriginal communities in Australia provided 337 GCS/GGS isolates that were emm sequence-typed. Lancefield group C isolates (GCS) were localized to specific households and group G isolates (GGS) were more evenly distributed. GCS/GGS was more frequently recovered from the throat than group A streptococci (GAS [S. pyogenes]) but rarely recovered from skin sores, and then only with Staphylococcus aureus or GAS. Symptomatic GGS/GGC pharyngitis was also rare. Specific emm sequence types of GCS/GGS did not appear to cycle through the communities (sequential strain replacement) in a manner suggesting acquisition of type-specific immunity. These communities already have high levels of streptococcal and poststreptococcal disease. GCS/GGS may increase in importance as it acquires key virulence factors from GAS by lateral gene transfer.
Highlights
Streptococcus dysgalactiae subsp. equisimilis is an increasingly recognized human pathogen, it may follow indirect pathways
Using molecular techniques to differentiate M protein classes, Bessen et al found that class I strains show a correlation with SOF-negative strains and contain serotypes associated with acute rheumatic fever (ARF) [9], whereas class II strains are associated with skin tropism
group G isolates (GGS)/group C isolates (GCS) was recovered from persons with 9 episodes of pyoderma, but always with Staphylococcus aureus, and in 2 persons with group A streptococci (GAS)
Summary
Streptococcus dysgalactiae subsp. equisimilis (groups C and G streptococci [GCS/GGS]) is an increasingly recognized human pathogen, it may follow indirect pathways. Specific emm sequence types of GCS/GGS did not appear to cycle through the communities (sequential strain replacement) in a manner suggesting acquisition of type-specific immunity. These communities already have high levels of streptococcal and poststreptococcal disease. Subsequent studies of the bacterial genome, including multilocus sequence typing of housekeeping genes, has demonstrated that large colony–forming human GCS and GGS are members of 1 species, S. dysgalactiae subsp. We used molecular typing to characterize the epidemiology of GCS/GGS throat carriage, pharyngitis, and skin infection in these communities and to examine their relationship to GAS epidemiology and ARF
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