[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: The results showed that eight S. suis strains isolated from humans were mainly serotype 2 (75.0%), while the rest were serotype 14 (25.0%). ST353 (62.5%) was the predominant genotype, followed by ST1 (25.0%) and ST7 (12.5%). All isolates belonged to the MCG1 group. The virulence genotypes of these isolates were primarily mrp(NA2)/sly+/ef+/gapdh+(75.0%), while the remaining 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. The cgSNP analysis indicated that these isolates were closer to the isolates from Guangdong, Zhejiang and Guangxi Provinces, with five ST353 strains and one ST7 strain belonging to Clade Ⅰ, and two ST1 strains belonging to Clade Ⅱ. Conclusion: The human isolates of S. suis in Henan Province are mainly ST353, harboring multiple virulence and antibiotic resistance genes.