Genome sequence and virulence factors of a group G Streptococcus dysgalactiae subsp. equisimilis strain with a new element carrying erm(B)

A Streptococcus dysgalactiae subsp. equisimilis (SDSE) strain WCHSDSE-1, which caused an outbreak of tonsillopharyngitis among healthcare workers in China, was subjected to genome sequencing and analysis. WCHSDSE-1 belongs to the Lancefield group G, emm type stG211.1 and sequence type 44. WCHSDSE-1 has virulence factors for adherence, impairing the recruitment of neutrophils to infection sites and toxins including streptolysins O and S and exotoxin G. WCHSDSE-1 has a 45.4-kb element resembling a conjugative transposon. This element is absent from other known SDSE genomes and contains the macrolide-resistant gene erm(B). Conjugative transfer of erm(B) was not successful in mating experiments, suggesting that the element might have lost its ability of conjugation. An almost identical element, which contains the tetracycline-resistant gene tet(M) instead of erm(B), is present on the genome of Filifactor alocis ATCC 35896. The boundaries and insertion sites of the two elements were identified and both were flanked by a 3-bp direct repeat, which is characteristic of transposition. In conclusion, the spectrum of virulence factors of WCHSDSE-1 is similar to other SDSE strains causing invasive diseases. WCHSDSE-1 possesses a new transposable element encoding macrolide resistance, which could pick up different resistance genes and could be transferred across species in oral microflora.