Prevalence, antimicrobial resistance, and genomic characterization of Streptococcus suis in swine herds of Guangxi, China.

Abstract

Streptococcus suis is a critical zoonotic pathogen that poses a significant threat to global public health and the swine industry. However, comprehensive epidemiological and genomic data on S. suis in swine herds across southern China remain limited. In this study, we conducted a large-scale surveillance of S. suis isolates from pig farms in Guangxi, China. A total of 210 S. suis isolates were recovered from 2706 throat swabs (7.76%) collected across 12 representative pig farms. Antimicrobial susceptibility testing revealed high resistance rates to erythromycin, trimethoprim/sulfamethoxazole, and florfenicol, with widespread multidrug resistance (MDR) phenotypes. Whole-genome sequencing (WGS) uncovered high diversity in predicted cps types and sequence types (STs). Furthermore, 21 antimicrobial resistance genes associated with seven antimicrobial classes were identified, with resistance genotypes largely correlating with the observed phenotypes. Notably, closely related isolates with minimal single-nucleotide polymorphism (SNP) variations were identified across geographically distinct farms, indicating the clonal dissemination of specific strains within the region. Global phylogenetic analysis demonstrated that the Guangxi isolates clustered closely with both swine- and human-derived strains from public databases. Taken together, these findings highlight the high prevalence, genetic heterogeneity, and extensive MDR profiles of S. suis in southern China, underscoring the critical need for continuous surveillance and prudent antimicrobial use under a One Health framework.