Pathogenetic characteristics of human isolates of Streptococcus suis in Henan Province from 2020 to 2023

Objective To investigate the pathogenetic characteristics of clinical isolates of Streptococcus suis in Henan Province from 2020 to 2023.Methods Eight clinical isolates of S. suis in Henan Province from 2020 to 2023 were identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and real-time fluorescence polymerase chain reaction (PCR). Serotype and virulence genes were detected by the serum agglutination test and PCR, and antibiotic susceptibility was evaluated using the microbroth dilution method. Multilocus sequence typing (MLST), minimum core genome (MCG), identification of antibiotic resistance genes and core genome single nucleotide polymorphism (cgSNP) analysis were conducted using whole genome sequencing.Results Among the 8 S. suis strains, serotype 2 accounted for 75.0%, followed by serotype 14 at 25.0%; ST353 (62.5%) was the predominant genotype, followed by ST1 (25.0%) and ST7 (12.5%); they all belonged to the MCG1 group; the main virulence genotypes were mrp(NA2)/sly+/ef+/gapdh+ (75.0%), and the rest were mrp(EU)/sly+/ef+/gapdh+ (25.0%); these isolates carried tetracycline, macrolide, lincosamide and aminoglycoside resistance genes, and their resistance rates to tetracycline, erythromycin and clindamycin were 100.0%, 87.5% and 87.5%, respectively, and 62.5% strains were intermediate-resistant to penicillin; cgSNP analysis indicated that these isolates were closer to the isolates from Guangdong, Zhejiang and Guangxi Provinces; five ST353 strains and one ST7 strain belonged to Clade I, whereas two ST1 strains belonged to Clade II.Conclusion The human isolates of S. suis in Henan Province were mainly ST353, which harbors multiple virulence and antibiotic resistance genes.