Abstract
Streptococcus suis is a zoonotic pathogen that causes invasive infections in humans and pigs. Although S. suis serotype 2 is prevalent among patient and swine infections, other serotypes are occasionally detected in humans. Of these, serotype 24 clonal complex (CC) 221/234 are recognized as emerging clones of human infection. Genomic exploration of three S. suis serotype 24 CC221/234 strains revealed antimicrobial resistance genes, pathotyping, virulence-associated gene (VAG) profiles, minimum core genome (MCG) typing, and comparison of the genomes. Based on these analyzes, all three serotype 24 strains were MCG7-3 and should be classified in the intermediate/weakly virulent (I/WV) group. All selected serotype 24 strains were susceptible to several antibiotics including β-lactam, fluoroquinolone, and chloramphenicol. Resistance to tetracycline, macrolide, and clindamycin was observed and attributed to the genes tet(O) and erm(B). Genomic comparison revealed the strains S12X, LSS66, LS0L, LS0E, 92–4,172, and IMT40201 that had phylogenetic affinity with serotype 24 CC221/234. Analysis of 80 virulence-associated genes (VAG) showed that all three serotype 24 strains lacked 24 genes consisting of adhesin P, epf, hyl, ihk, irr, mrp, nadR, neuB, NisK/R, ofs, permease (SSU0835), rgg, revS, salK/R, sao, sly, spyM3_0908, srtBCD, srtF, srtG, SSU05_0473, virA, virB4, and virD4. Eleven specific sequences were identified in the 3 serotype 24 genomes that differed from the genomes of the representative strains of epidemic (E; SC84), highly virulent (HV; P1/7), I/WV (89–1,591), and avirulent (T15 and 05HAS68).
Highlights
Streptococcus suis, an important swine pathogen, causes invasive infections in humans who have been in close contact with infected pigs or contaminated pork-derived products (Goyette-Desjardins et al, 2014)
Most human clinical sequence types (STs) are grouped into limited clonal complexes (CCs) consisting of CC1, CC16, CC94, CC20, CC25, CC28, CC104, CC221/234, and CC233/379 (Okura et al, 2016; Hatrongjit et al, 2020)
ST7 (CC1), responsible for the 1998 and 2005 epidemics, was mostly present in China, while CC16 and CC94 were predominant in Europe, human cases were reported in Thailand (Hatrongjit et al, 2020)
Summary
Streptococcus suis, an important swine pathogen, causes invasive infections in humans who have been in close contact with infected pigs or contaminated pork-derived products (Goyette-Desjardins et al, 2014). Human cases have been reported due to the rare serotypes 4, 5, 7, 9, 14, 16, 21, 24, and 31 (Nghia et al, 2008; Callejo et al, 2014; Goyette-Desjardins et al, 2014; Hatrongjit et al, 2015; Kerdsin et al, 2017; Liang et al, 2021). We reported three human cases of S. suis serotype 24 that belonged to the clonal complex (CC) 221/234 (Kerdsin et al, 2018). Seven human cases infected by S. suis CC221/234 strains have been reported; five of them were serotype 24 and the rest belonged to serotypes 5 and 31 (Kerdsin et al, 2011, 2016, 2018; Hatrongjit et al, 2015). This study could provide insight into genomic characteristics, putative virulence genes, genetic relationships, and the prediction of pathogenic capacity of this serotype
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