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Horizontal transfer of ΦHKU.vir and its role in the evolution of acapsular emm89 group A Streptococcus in Taiwan
Chuan Chiang-Ni1,2,3, Chien-Chung Lee4,5,6, Chia-Yu Chi7,8
1Department of Microbiology and Immunology, College of Medicine, Chang Gung University, No. 259 Wen-Hwa 1st Road, Kwei-Shan, Taoyuan, 333323, Taiwan. entchuan@gap.cgu.edu.tw.
Introduction:
The global resurgence of scarlet fever and invasive group A Streptococcus (GAS) infections has been noted over the past decade. In East Asia, specifically in Hong Kong and China, emm12 isolates that acquired prophage ΦHKU.vir, which carried SSA, SpeC, and Spd1 exotoxins, were over-presented in scarlet fever cases. The prevalence of ssa-positive emm12 isolates was increased significantly in Taiwan; however, it remains unclear whether this increase is mediated by the horizontal transfer of ΦHKU.vir homologs or the expansion of Hong Kong scarlet fever-associated emm12 isolates.
Materials And Methods:
This study included 240 non-emm1 isolates in Taiwan during 2009-2023. The genome and prophage sequences of clinical isolates were analyzed by whole genome sequencing.
Results:
The prophages carried ssa, speC, and spd1 in Taiwan emm12 isolates shared high nucleotide sequence identity with ΦHKU.vir. All analyzed emm12 isolates in Taiwan were phylogenetically closely related to Hong Kong emm12 isolates, suggesting that Taiwan ssa-positive emm12 isolates shared a common origin with those from Hong Kong. This study further identified ΦHKU.vir homologs in emm90 and acapsular emm89 isolates. Although the acquisition of ΦHKU.vir is related to the expansion of emm12 isolates in Hong Kong, this study suggests that the prophage exotoxin SSA did not have significant roles in enhancing bacterial cytotoxicity and intracelluar survival of the acapsular emm89 strains.
Conclusions:
The acquisition of prophages is important for the evolution of GAS. Monitoring the expansion of ΦHKU.vir in non-emm1/emm12 isolates is essential, as studying its impact on GAS pathogenicity will help in preventing and controlling GAS infections.
Insights
Group A Streptococcus (GAS) infections are rising globally. This study found that Taiwan
Area of Science:
- Microbiology
- Genomics
- Epidemiology
Background:
- Global resurgence of scarlet fever and invasive group A Streptococcus (GAS) infections.
- Over-representation of emm12 isolates carrying ΦHKU.vir prophage with exotoxins in East Asian scarlet fever cases.
- Increased prevalence of ssa-positive emm12 isolates in Taiwan, with unclear transmission dynamics.
Purpose of the Study:
- Investigate the origin and spread of ssa-positive emm12 isolates in Taiwan.
- Determine if the increase in Taiwan is due to horizontal gene transfer or clonal expansion.
- Identify the presence of ΦHKU.vir homologs in other GAS strains.
Main Methods:
- Whole genome sequencing of 240 non-emm1 GAS isolates from Taiwan (2009-2023).
- Analysis of prophage and genome sequences.
- Phylogenetic analysis to compare isolates with international strains.
Main Results:
- Taiwanese emm12 isolates carrying ssa, speC, and spd1 showed high sequence identity to ΦHKU.vir.
- Taiwanese emm12 isolates are phylogenetically linked to Hong Kong isolates, suggesting a common origin.
- ΦHKU.vir homologs were found in emm90 and acapsular emm89 isolates; SSA did not significantly enhance cytotoxicity in emm89.
Conclusions:
- Prophage acquisition is crucial for GAS evolution.
- Monitoring ΦHKU.vir expansion in non-emm1/emm12 isolates is vital.
- Understanding ΦHKU.vir's impact on GAS pathogenicity is key for infection control.
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