Horizontal transfer of ΦHKU.vir and its role in the evolution of acapsular emm89 group A Streptococcus in Taiwan.

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.