Infectious diseases & immunity · 2026
Comparing virulence profile of dominant emm1 and emm12 group A streptococcus strains associated with scarlet fever in Shanghai.
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Zhou Xingyu, Cai Jiehao, Lu Yanyan, Huang Jiebin, Zeng Mei, Chen Mingliang
Аннотация
BACKGROUND: An increased incidence of group A Streptococcus-related scarlet fever has been observed in Shanghai since 2011, characterized by the co-circulation of both emm12 and emm1 strains. The comparative virulence potential of these two dominant strains, which is critical for understanding their dynamics and severity, remains largely under researched. This study aimed to systematically compare their virulence determinants to uncover the molecular basis for their successful dissemination.
METHODS: As the dominant strains that cause scarlet fever, 16 isolates each of both emm1 and emm12 were selected from the Children's Hospital at Fudan University between 2011 and 2022 using a stratified random sampling method. We compared the two strain types in terms of the positivity rate of virulence factors, adherence and internalization capacity into epithelial cells, biofilm formation capacity, and resistance to innate immune responses.
RESULTS: Genomic analysis revealed significant divergence between the emm1 and emm12 strains, particularly within the fibronectin-collagen-T antigen (FCT) region and fibronectin-binding protein and superantigen genes. These genetic differences were reflected in functionally distinct phenotypes. Emm1 strains (linked to FCT2) exhibited a superior colonization capacity, demonstrating rates of epithelial cell adherence and internalization that were approximately two-folds higher, and significantly enhanced biofilm formation compared to emm12 strains (linked to FCT4; P < 0.05). Furthermore, emm1 strains showed significantly greater resistance to innate immune clearance, with higher survival rates in human whole blood, serum, and phagocytic cells (P < 0.001).
CONCLUSIONS: The enhanced in vitro colonization and immune evasion fitness of emm1 strains are likely attributable to their distinct virulence gene repertoire and expression profile. These findings suggest that the co-dominance of emm1 and emm12 may be driven by divergent pathogenic strategies. The continuous investigation of shifts in the prevalence of emm types and associated virulence factors is essential for understanding their epidemiology and informing strategies for controlling scarlet fever.
METHODS: As the dominant strains that cause scarlet fever, 16 isolates each of both emm1 and emm12 were selected from the Children's Hospital at Fudan University between 2011 and 2022 using a stratified random sampling method. We compared the two strain types in terms of the positivity rate of virulence factors, adherence and internalization capacity into epithelial cells, biofilm formation capacity, and resistance to innate immune responses.
RESULTS: Genomic analysis revealed significant divergence between the emm1 and emm12 strains, particularly within the fibronectin-collagen-T antigen (FCT) region and fibronectin-binding protein and superantigen genes. These genetic differences were reflected in functionally distinct phenotypes. Emm1 strains (linked to FCT2) exhibited a superior colonization capacity, demonstrating rates of epithelial cell adherence and internalization that were approximately two-folds higher, and significantly enhanced biofilm formation compared to emm12 strains (linked to FCT4; P < 0.05). Furthermore, emm1 strains showed significantly greater resistance to innate immune clearance, with higher survival rates in human whole blood, serum, and phagocytic cells (P < 0.001).
CONCLUSIONS: The enhanced in vitro colonization and immune evasion fitness of emm1 strains are likely attributable to their distinct virulence gene repertoire and expression profile. These findings suggest that the co-dominance of emm1 and emm12 may be driven by divergent pathogenic strategies. The continuous investigation of shifts in the prevalence of emm types and associated virulence factors is essential for understanding their epidemiology and informing strategies for controlling scarlet fever.