Incidence and Effects of Acquisition of the Phage-Encoded ssa Superantigen Gene in Invasive Group A Streptococcus

Abstract

The acquisition of the phage-encoded superantigen ssa by scarlet fever-associated group A Streptococcus (Streptococcus pyogenes, GAS) is found in North Asia. Nonetheless, the impact of acquiring ssa by GAS in invasive infections is unclear. This study initially analyzed the prevalence of ssa+ GAS among isolates from sterile tissues and blood. Among 220 isolates in northern Taiwan, the prevalence of ssa+ isolates increased from 1.5% in 2008–2010 to 40% in 2017–2019. Spontaneous mutations in covR/covS, which result in the functional loss of capacity to phosphorylate CovR, are frequently recovered from GAS invasive infection cases. Consistent with this, Phostag western blot results indicated that among the invasive infection isolates studied, 10% of the ssa+ isolates lacked detectable phosphorylated CovR. Transcription of ssa is upregulated in the covS mutant. Furthermore, in emm1 and emm12 covS mutants, ssa deletion significantly reduced their capacity to grow in human whole blood. Finally, this study showed that the ssa gene could be transferred from emm12-type isolates to the emm1-type wild-type strain and covS mutants through phage infection and lysogenic conversion. As the prevalence of ssa+ isolates increased significantly, the role of streptococcal superantigen in GAS pathogenesis, particularly in invasive covR/covS mutants, should be further analyzed.

The Bacterial Markers of Identification of Invasive CovR/CovS-Inactivated Group A Streptococcus

“…Our previous study identified, by Phostag Western blotting ( Fig. 1B ), 29 CovS-inactivated clinical isolates ( 31 ). In this study, we found that only nine isolates (31%) exhibited a distinguishable encapsulated colony morphology ( Fig.…”

“…Strain AP3 is a mouse-passaged isolate of A20 which has a frameshift deletion in the covS gene ( 33 ) and was designed as the covS mutant in this study. The rocA mutant, RocA-truncated mutant, hasA mutants, and CovR/CovS-inactivated clinical isolates have been described previously ( 26 , 31 , 33 ). GAS strains were cultured on Trypticase soy agar containing 5% sheep blood or in tryptic soy broth (Becton, Dickinson and Co., Sparks, MD, USA) supplemented with 0.5% yeast extract (TSBY).…”

Nationwide upsurge in invasive disease in the context of longitudinal surveillance of carriage and invasiveStreptococcus pyogenes2009-2023, the Netherlands: a molecular epidemiological study

“…This new clone can be differentiated from M1global by 27 lineage-defining single-nucleotide polymorphisms (SNP) and is characterized by increased SpeA production (11,17), resulting from a SNP in the transfermessenger RNA gene ssrA (15). Numerous countries, including the United States, Canada, the Netherlands, Australia, and Taiwan, have reported on the presence and expansion of the M1UK lineage among iGAS patients, confirming global dissemination and further evolution of this new variant (15,(18)(19)(20)(21).…”