AUTHOR=Chiang-Ni Chuan , Liu Yen-Shan , Lin Chieh-Yu , Hsu Chih-Yun , Shi Yong-An , Chen Yi-Ywan M. , Lai Chih-Ho , Chiu Cheng-Hsun 

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

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.685343

DOI=10.3389/fmicb.2021.685343

ISSN=1664-302X

ABSTRACT=<p>The acquisition of the phage-encoded superantigen <italic>ssa</italic> by scarlet fever-associated group A <italic>Streptococcus</italic> (<italic>Streptococcus pyogenes</italic>, GAS) is found in North Asia. Nonetheless, the impact of acquiring <italic>ssa</italic> by GAS in invasive infections is unclear. This study initially analyzed the prevalence of <italic>ssa</italic>+ GAS among isolates from sterile tissues and blood. Among 220 isolates in northern Taiwan, the prevalence of <italic>ssa</italic>+ isolates increased from 1.5% in 2008–2010 to 40% in 2017–2019. Spontaneous mutations in <italic>covR</italic>/<italic>covS</italic>, 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 <italic>ssa</italic>+ isolates lacked detectable phosphorylated CovR. Transcription of <italic>ssa</italic> is upregulated in the <italic>covS</italic> mutant. Furthermore, in <italic>emm</italic>1 and <italic>emm</italic>12 <italic>covS</italic> mutants, <italic>ssa</italic> deletion significantly reduced their capacity to grow in human whole blood. Finally, this study showed that the <italic>ssa</italic> gene could be transferred from <italic>emm</italic>12-type isolates to the <italic>emm</italic>1-type wild-type strain and <italic>covS</italic> mutants through phage infection and lysogenic conversion. As the prevalence of <italic>ssa</italic>+ isolates increased significantly, the role of streptococcal superantigen in GAS pathogenesis, particularly in invasive <italic>covR/covS</italic> mutants, should be further analyzed.</p>