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Streptococcus suis, a swine pathogen that causes zoonotic infections in Europe and Asia, has increasingly been observed in South America. We reviewed all available reports from the continent and identified S. suis cases in Argentina, Brazil, Chile, French Guiana, and Uruguay. We also identified 8 novel infections from Argentina, bringing the total documented human cases in South America to 47. We reclassified 1 previously reported infection as S. parasuis. Among the 47 S. suis cases, 40 (85%) patients had meningitis, 2 (4%) had toxic shock-like illness, 2 (4%) had nonshock sepsis, 1 (2%) had arthritis, and 1 (2%) had endocarditis. The case-fatality rate was 4% (2/47). Infections were primarily linked to pig or pork exposure, although some occurred after consuming undercooked meat. Case distribution varied by country, and Argentina reported a disproportionately high number of cases despite a smaller swine industry. Our findings highlight the need for more consistent regional S. suis surveillance.

Streptococcus parasuis ( S. parasuis ) is a close relative of Streptococcus suis ( S. suis ), composed of former members of S. suis serotypes 20, 22 and 26. S. parasuis could infect pigs and cows, and recently, human infection cases have been reported, making S. parasuis a potential opportunistic zoonotic pathogen. In this study, we analysed the genomic characteristics of S. parasuis , using pan-genome analysis, and compare some phenotypic determinants such as capsular polysaccharide, integrative conjugative elements, CRISPR-Cas system and pili, and predicted the potential virulence genes by associated analysis of the clinical condition of isolated source animals and genotypes. Furthermore, to discuss the relationship with S. suis , we compared these characteristics of S. parasuis with those of S. suis . We found that the characteristics of S. parasuis are similar to those of S. suis , both of them have “open” pan-genome, their antimicrobial resistance gene profiles are similar and a srtF pilus cluster of S. suis was identified in S. parasuis genome. But S. parasuis still have its unique characteristics, two novel pilus clusters are and three different type CRISPR-Cas system were found. Therefore, this study provides novel insights into the interspecific and intraspecific genetic characteristics of S. parasuis , which can be useful for further study of this opportunistic pathogen, such as serotyping, diagnostics, vaccine development, and study of the pathogenesis mechanism.

(1) Background: S. parasuis is a potential opportunistic zoonotic pathogen that can infect pigs, cattle, and humans, composed of former members of S. suis serotypes 20, 22, and 26. In recent years, unclassified serotypes and a serotype 11 S. parasuis have been discovered. (2) Methods: We characterized two S. parasuis strains (FZ1 and FZ2) isolated from brain samples of paralyzed pigs and examined evolutionary divergence among 22 available S. parasuis and 8 serotype 2 S. suis genomes through whole-genome sequencing and comparative genomic analysis. We compared virulence genes (VGs) and antibiotic resistance genes (ARGs) and analyzed mobile genetic elements (MGEs) in FZ1 and FZ2. (3) Results: Comparative genomics revealed that srtC, ctpV, and sugC may represent key virulence determinants in S. parasuis, although their pathogenic potential appears attenuated compared to serotype 2 S. suis. In addition, S. parasuis exhibited primary resistance to aminoglycosides, macrolides, tetracyclines, and oxazolidinones, while demonstrating heightened susceptibility to oxazolidinone-class antibiotics. Moreover, we found an important association between MGEs and antibiotic resistance in S. parasuis FZ1 and FZ2. (4) Conclusions: This study provides new insights into the genomic and evolutionary characteristics of S. parasuis and provides a new basis for the study of bacterial pathogenesis and drug resistance in the future.

Streptococcus parasuis is currently not only an underestimated zoonotic pathogen but also a bacterial source of infection in food animals, posing a potential threat to global public health. Despite increased reports in recent years, systematic studies in Northwest China remain scarce. However, the lack of complete genomic sequence information has limited in-depth bioinformatics analysis of multidrug-resistant S. parasuis isolated from pigs. This study reports the whole-genome sequencing results of S. parasuis strain A1 isolated from pigs. The A1 genome consists of a single circular chromosome without circular plasmids, establishing it as a potential “blank” vector for constructing standardized gene cloning and expression systems in genetic engineering. Twenty-one antibiotic resistance genes were identified on the bacterial chromosome, conferring resistance to major antibiotics including glycopeptides, macrolides, lincosamides, streptogramins, aminoglycosides, tetracyclines, fluoroquinolones, cephalosporins, polypeptides, and β-lactams. Resistance mechanisms encompass target site modification, target site protection, antibiotic inactivation, and efflux pump-mediated drug efflux, demonstrating potent multidrug resistance potential. Additionally, 113 virulence factors were identified, spanning multiple functional domains including effector protein secretion systems, immune regulation, adhesion, stress survival, and biofilm formation. Among these, six virulence factors relate to nutritional metabolism, primarily involving iron uptake, pyrimidine biosynthesis, purine biosynthesis, and fatty acid metabolism. Antibiotic susceptibility testing confirmed the multidrug-resistant phenotype of this strain. Mouse infection experiments demonstrated that strain A1 exhibits strong pathogenicity, causing lethal infections in mice and significant histopathological damage to organs such as the liver and spleen. Concurrently, levels of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) were significantly elevated in the serum of infected mice. Whole-genome analysis revealed 24 horizontal gene transfer elements in A1, including 3 genomic islands, 13 transposons, and 8 remnant pre-phage sequences. Furthermore, 196 virulence-attenuating mutations and 10 potential pathogenicity-related deletion sites were identified. Therefore, this study contributes to the development of strategies for preventing and controlling S. parasuis infections and their spread within pig populations. It should be emphasized that this study is based solely on analysis of a single strain, and the generalizability of its conclusions requires validation with additional strains. Furthermore, the correspondence between resistance genes and phenotypes, as well as the specific regulatory and synergistic mechanisms of virulence factors, remain incompletely elucidated and warrant further investigation.

This study was performed to investigate the presence and characteristics of the oxazolidinone resistance genes optrA and cfr(D) in Streptococcus parasuis. In total, 36 Streptococcus isolates (30 Streptococcus suis isolates, 6 Streptococcus parasuis isolates) were collected from pig farms in China in 2020–2021, using PCR to determine the presence of optrA and cfr. Then, 2 of the 36 Streptococcus isolates were further processed as follows. Whole-genome sequencing and de novo assembly were employed to analyze the genetic environment of the optrA and cfr(D) genes. Conjugation and inverse PCR were employed to verify the transferability of optrA and cfr(D). The optrA and cfr(D) genes were identified in two S. parasuis strains named SS17 and SS20, respectively. The optrA of the two isolates was located on chromosomes invariably associated with the araC gene and Tn554, which carry the resistance genes erm(A) and ant(9). The two plasmids that carry cfr(D), pSS17 (7550 bp) and pSS20-1 (7550 bp) have 100% nucleotide sequence identity. The cfr(D) was flanked by GMP synthase and IS1202. The findings of this study extend the current knowledge of the genetic background of optrA and cfr(D) and indicate that Tn554 and IS1202 may play an important role in the transmission of optrA and cfr(D), respectively.

( ) and ( ) are prevalent pathogens in pig populations and are often associated with co-infections, leading to substantial economic losses in the swine industry. However, there is currently a shortage of rapid detection methods. In this study, a dual loop-mediated isothermal amplification combined with lateral flow dipstick (LAMP-LFD) assay was developed for the simultaneous and convenient detection of S. suis and G. parasuis. The assay utilized primers targeting the conserved regions of the gdh gene of S. suis and the infB gene of . Optimal primer sets were identified, and reaction conditions, including temperature, time, and primer concentration ratios, were optimized using single-variable control method. The LAMP-LFD assay was established with biotin and digoxin or biotin and 6-FAM-labeled FIP/BIP primers, combined with LFD. The assay was most effective at a reaction temperature of 62°C, a primer concentration ratio of 1:4, and a reaction time of 40 minutes. The minimum detection limits were 22 and 18 copies/μL for recombinant plasmids and 19 and 20 CFU for bacterial samples of S. suis and G. parasuis, respectively. The assay showed no cross-reactivity with other pathogens and exhibited high adaptability across various thermal platforms, including PCR instruments, metal baths, and water baths. Clinical testing of 106 samples revealed positive rates of 11.32% (12/106) for S. suis, 25.47% (27/106) for , and 2.83% (3/106) for mixed infections. This simple, rapid, specific, and sensitive dual LAMP-LFD assay provides robust technical support for the prevention and control of swine streptococcosis and Glässer's disease.

( ), is a key respiratory pathogen responsible for Glässer's disease in pigs, characterized by polyserositis, arthritis, and pulmonary lesions. While it disrupts the respiratory microbiota, its impact on the gut-lung axis, a critical pathway for systemic immune and metabolic crosstalk, remains unexplored. We established a piglet infection model using the highly virulent G. parasuis strain XX0306 (serotype 5). Systemic effects were investigated through integrated 16S rDNA sequencing of the lung and gut microbiota, complemented by untargeted metabolomics of intestinal contents. We performed histopathological examination and measured serum biomarkers (diamine oxidase and D-lactate) to assess intestinal barrier integrity. Correlation analysis linked microbial shifts to host metabolic alterations. Infection induced profound dysbiosis in both the lung and gut microbiota. Pulmonary microbial diversity and functional potential declined. Gut dysbiosis featured a loss of beneficial bacteria and enrichment of potential pathogens (e.g., , , ). Functional prediction indicated significant alterations in 12 gut microbial metabolic pathways, with downregulated amino acid metabolism and upregulated carbohydrate/lipid metabolism and xenobiotic degradation. Metabolomics identified 30 differentially abundant metabolites (e.g., argininosuccinate, liquiritigenin, citrulline), primarily enriched in cytochrome P450-mediated xenobiotic metabolism and arginine biosynthesis. Argininosuccinate levels correlated with pathogenic genera ( , , ). Infected piglets exhibited significant intestinal barrier damage, evidenced by elevated serum diamine oxidase (DAO) and D-lactate (D-LA). This study demonstrates that infection extensively remodels the gut-lung axis microbiota and host metabolome, leading to intestinal barrier impairment. The perturbation of arginine biosynthesis may compromise host immunity. These results provide novel mechanistic insights into the pathogenesis of Glässer's disease.

Porcine respiratory disease complex is a multifactorial disease syndrome in swine in which bacterial pathogens play important roles. Among them, Streptococcus suis (SS), Glaesserella parasuis (GPS), and Actinobacillus pleuropneumoniae (APP) are important bacterial agents associated with respiratory disease in pigs, underscoring the need for a rapid, accurate, and simultaneous detection method. In this study, we developed a triplex real‐time PCR assay for the simultaneous detection of SS, GPS, and APP, and evaluated its performance in tonsil samples from clinically healthy pigs. The assay showed high specificity, sensitivity, and reproducibility. A total of 228 tonsil samples were analyzed in parallel by triplex real‐time PCR assay and conventional PCR assay. The triplex real‐time PCR assay detected at least one of the three pathogens in 91.23% (208/228) of samples, which was markedly higher than the 73.68% (168/228) detected by PCR assay. Concurrent detection of multiple pathogens was observed in 98 samples (42.98%) by the triplex real‐time PCR assay, including 82 samples positive for both SS and GPS (35.96%) and 16 samples positive for SS, GPS, and APP (7.02%). From the triple‐positive samples, 12 SS isolates were recovered, of which 91.67% (11/12) were multidrug‐resistant. Animal challenge experiments further confirmed the virulence of two representative isolates, SZWUSS183 ( cps type 1/2, ST7) and SZWUSS225 ( cps type 3, ST117). Overall, the developed triplex real‐time PCR assay provides a sensitive and reliable tool for the simultaneous detection of these major bacterial pathogens and may facilitate surveillance of their circulation and co‐occurrence in swine herds.

Streptococcus suis is a worldwide pathogen that impacts the swine industry, causing severe clinical signs, including meningitis and arthritis, in postweaning piglets. A key virulence mechanism of S. suis is biofilm formation, which improves its persistence and resistance to external factors. Here, we assessed the in vitro biofilm formation of 240 S. suis isolates from Spanish swine farms and evaluated the effects of serovars (SVs) and coinfections with other porcine respiratory disease complex (PRDC) pathogens. Our study revealed significant heterogeneity in biofilm formation among S. suis SVs. Notably, SV2 resulted in the lowest degree of biofilm formation, in contrast with the high biofilm-forming capacities of SV1, SV7, and SV9. Other PRDC pathogens, including Actinobacillus pleuropneumoniae , Glaesserella parasuis , and Pasteurella multocida , formed biofilms, although they were generally less robust than those of S. suis (except for SV2), which contrasts with the high biofilm formation of Staphylococcus hyicus . Coinfections enhanced biofilm formation in mixed cultures of S. suis , particularly with P. multocida . Other coinfections revealed variable results in pathogen interactions, suggesting the potential of biofilms for increased persistence and pathogenicity in coinfections. In conclusion, this study underscores the importance of serovar-specific differences in biofilm formation among S. suis isolates, with significant implications for pathogenicity and persistence. The heterogeneous biofilm formation observed in coinfections with other PRDC pathogens reveals a complex interplay that could exacerbate disease severity. These findings provide a foundation for further research on biofilm mechanisms to mitigate the impact of PRDC in the swine industry.

Glaesserella parasuis ( G. parasuis ) can elicit serious inflammatory responses and cause meningitis in piglets. Previous epigenetic studies have indicated that alterations in host DNA methylation may modify the inflammatory response to bacterial infection. However, to date, genome-wide analysis of the DNA methylome during meningitis caused by G. parasuis infection is still lacking. In this study, we employed an unbiased approach using deep sequencing to profile the DNA methylome and transcriptome from G. parasuis infected porcine brain (cerebrum) and integrated the data to identify key differential methylation regions/sites involved in the regulation of the inflammatory response. Results showed that DNA methylation patterns and gene expression profiles from porcine brain were changed after G. parasuis infection. The majority of the altered DNA methylation regions were found in the intergenic regions and introns and not associated with CpG islands, with only a low percentage occurring at promoter or exon regions. Integrated analysis of the DNA methylome and transcriptome identified a number of inversely and positively correlated genes between DNA methylation and gene expression, following the criteria of |log 2 FC| > 0.5, |diffMethy| > 0.1, and P < 0.05. Differential expression and methylation of two significant genes, semaphoring 4D ( SEMA4D ) and von Willebrand factor A domain containing 1 ( VWA1 ), were validated by qRT-PCR and bisulfite sequencing. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses demonstrated that DNA methylation inversely correlated genes in G. parasuis infected porcine brains were mainly involved with cell adhesion molecules (CAMs), bacterial invasion of epithelial cells, RIG-1-like receptor signaling pathways, and hematopoietic cell lineage signaling pathways. In addition, a protein-protein interaction network of differentially methylated genes found potential candidate molecular interactions relevant to the pathology of G. parasuis infection. To the best of our knowledge, this is the first attempt to integrate the DNA methylome and transcriptome data from G. parasuis infected porcine brains. Our findings will help understanding the contribution of genome-wide DNA methylation to the pathogenesis of meningitis in pigs and developing epigenetic biomarkers and therapeutic targets for the treatment of G. parasuis induced meningitis.