AUTHOR=Zhang Yuwei , Lv FenFen , Su Yan , Zhang Huan , Zhang Baojiang 

TITLE=Complete genome sequencing and comparative genomic analysis of three donkey Streptococcus equi subsp. equi isolates

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1285027

DOI=10.3389/fmicb.2023.1285027

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p><italic>Streptococcus equi</italic> subspecies <italic>equi</italic> (<italic>S. equi</italic>) is the causative agent of strangles, which is one of the most common and highly contagious respiratory infectious illnesses in horses. <italic>Streptococcus equi</italic> (<italic>S. equi</italic>) is a horse-specific pathogen that originated from the closely related zoonotic pathogen <italic>Streptococcus equi</italic> subspecies <italic>zooepidemicus</italic> (<italic>S. zooepidemicus</italic>). Despite decades of research, the movement of genetic material across host-restricted diseases remains a mystery.</p></sec><sec><title>Methods</title><p>Three <italic>S. equi</italic> donkey isolates (HTP133, HTP232, and HT1112) were recently isolated from a strangles epidemic on donkey farms in China’s Xinjiang Province. In this study, we performed a comprehensive comparative analysis of these isolates using whole genome sequencing and compared them to the published genomic sequences of equine strain <italic>S. equi</italic> 4047 to uncover evidence of genetic events that shaped the evolution of these donkey <italic>S. equi</italic> isolates’ genomes.</p></sec><sec><title>Results</title><p>Whole genome sequencing indicated that both strains were closely related, with comparable gene compositions and a high rate of shared core genomes (1788-2004). Our comparative genomic study indicated that the genome structure is substantially conserved across three donkey strains; however, there are several rearrangements and inversions when compared to the horse isolate <italic>S. equi</italic> 4047. The virulence factors conveyed by genomic islands and prophages, in particular, played a key role in shaping the pathogenic capacity and genetic diversity of these <italic>S. equi</italic> strains. Furthermore, we discovered that the HT133 isolate had a strong colonization ability and increased motility; the HT1112 isolates had a significantly higher ability for antimicrobial resistance and biofilm formation, and the HT232 isolate gained pathogenic specialization by acquiring a bacteriophage encoding hyaluronate lyase.</p></sec><sec><title>Discussion</title><p>In summary, our findings show that genetic exchange across <italic>S. equi</italic> strains influences the development of the donkey <italic>S. equi</italic> genome, offering important genetic insights for future epidemiological studies of <italic>S. equi</italic> infection.</p></sec>