BackgroundStreptococcus suis (S. suis) is a major swine pathogen and an emerging zoonotic agent. Serotypes 1, 2, 3, 7, 9, 14 and 1/2 are the most prevalent serotypes of this pathogen. However, almost all studies were carried out on serotype 2 strains. Therefore, characterization of genomic features of other serotypes will be required to better understand their virulence potential and phylogenetic relationships among different serotypes.ResultsFour Chinese S. suis strains belonging to serotypes 1, 7, 9 and 1/2 were sequenced using a rapid, high-throughput approach. Based on the 13 corresponding serotype strains, including 9 previously completed genomes of this bacterium, a full comparative genomic analysis was performed. The results provide evidence that (i) the pan-genome of this species is open and the size increases with addition of new sequenced genomes, (ii) strains of serotypes 1, 3, 7 and 9 are phylogenetically distinct from serotype 2 strains, but all serotype 2 strains, plus the serotype 1/2 and 14 strains, are very closely related. (iii) all these strains, except for the serotype 1 strain, could harbor a recombinant site for a pathogenic island (89 K) mediated by conjugal transfer, and may have the ability to gain the 89 K sequence.ConclusionsThere is significant genomic diversity among different strains in S. suis, and the gain and loss of large amount of genes are involved in shaping their genomes. This is indicated by (i) pairwise gene content comparisons between every pair of these strains, (ii) the open pan-genome of this species, (iii) the observed indels, invertions and rearrangements in the collinearity analysis. Phylogenetic relationships may be associated with serotype, as serotype 2 strains are closely related and distinct from other serotypes like 1, 3, 7 and 9, but more strains need to be sequenced to confirm this.

Background Streptococcus suis infections are a serious problem for both humans and pigs worldwide. The emergence and increasing prevalence of antibiotic-resistant S. suis strains pose significant clinical and societal challenges.ResultsIn our study, we sequenced one multi-drug-resistant S. suis strain, R61, and one S. suis strain, A7, which is fully sensitive to all tested antibiotics. Comparative genomic analysis revealed that the R61 strain is phylogenetically distinct from other S. suis strains, and the genome of R61 exhibits extreme levels of evolutionary plasticity with high levels of gene gain and loss. Our results indicate that the multi-drug-resistant strain R61 has evolved three main categories of resistance.ConclusionsComparative genomic analysis of S. suis strains with diverse drug-resistant phenotypes provided evidence that horizontal gene transfer is an important evolutionary force in shaping the genome of multi-drug-resistant strain R61. In this study, we discovered novel and previously unexamined mutations that are strong candidates for conferring drug resistance. We believe that these mutations will provide crucial clues for designing new drugs against this pathogen. In addition, our work provides a clear demonstration that the use of drugs has driven the emergence of the multi-drug-resistant strain R61.

Streptococcus suis is an important zoonotic agent leading to a variety of diseases in swine and can be transmitted to human beings upon close contact. Here, we report the complete genome sequence of S. suis serotype 14 strain JS14 which was isolated from a diseased pig in Jiangsu Province, China.

Streptococcus suis is a zoonotic pathogen causing economic loss in the swine industry and is also a threat to human health. To date, the mechanism of pathogenesis is not fully understood. Here, we report the complete genome sequence of S. suis strain ST3 of serotype 3, which provides opportunities to reveal genetic basis of infection of S. suis non-serotype 2 strains.Streptococcus suis is an important swine pathogen and causes various diseases, such as meningitis, pneumonia, arthritis, etc. (8). Moreover, S. suis is an emerging zoonotic agent and can lead to human infection. Among the 33 serotypes of S. suis (types 1 to 31, 33, and 1/2), serotype 3 is more prevalent than the others, in addition to serotype 2 strains (6,14). For further understanding on the genetic background of the serotypic diversity and pathogenic potential of serotype 3 strains, S. suis ST3, isolated from a pig with pneumonia in Hubei province, China, was chosen for genome sequencing.The genome sequence was determined by an Illumina genome analyzer at Beijing Institute of Genomics. The assembly that was produced by SOAPdenovo1.04 was based on 23,334,073 paired-end reads with a read length of 79 bp and an average insertion size of 500 bp. The resulting 73 large contigs were aligned to the published genome of S. suis 05ZYH33 using MUMmer3 (10) to obtain linkage information. Gaps were closed by primer walking and sequencing of PCR products. Glimmer 3.02 (5) and GeneMarkS (2) were used to predict open reading frames (ORFs) (results were amalgamated). Annotation was performed by comparing ORFs with those in nonredundant-protein databases (the KEGG and COG databases). tRNAs and rRNAs were predicted by tRNAscan-SE 1.21 (12) and RNAmmer 1.2 (11), respectively.The genome of strain ST3 is composed of one circular chromosome of 2,028,815 bp, with a GC content of 41.29%. There are 2,031 protein-coding sequences (CDSs) that account for 87.8% of the genome, with an average length of 877 bp, 54 tRNAs, 4 rRNA loci, and 28 insertion (IS) elements.There are many genes unique to ST3 compared to other sequenced S. suis strains, including a MATE efflux family protein, two transcriptional regulators, and several ABC transporter proteins. Moreover, several genes that located in the cps locus, such as genes encoding a glycosyl transferase family 2 protein and a cps synthesis protein, also share poor homology with that of other S. suis strains and may reveal a distinct role in capsular structure determination for this serotype. Other genes unique to ST3 were characterized by hypothetical protein or phage protein.The previously identified 89K pathogenicity island region in S. suis (3) was not found in ST3, but several virulenceassociated genes were included in it, such as pgdA, which can result in escaping of recognition and increased resistance to lysozyme by modification of peptidoglycan (7), and fbps, which plays a role in colonization of the organs (4). Also, srtA, which encodes an enzyme involved in protein sorting and adherence to host epithelial cells thus asso...