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BackgroundSwine extraintestinal pathogenic Escherichia coli (ExPEC) is an important pathogen that leads to economic and welfare costs in the swine industry worldwide, and is occurring with increasing frequency in China. By far, various virulence factors have been recognized in ExPEC. Here, we investigated the virulence genotypes and clonal structure of collected strains to improve the knowledge of phylogenetic traits of porcine ExPECs in China.ResultsWe isolated 64 Chinese porcine ExPEC strains from 2013 to 14 in China. By multiplex PCR, the distribution of isolates belonging to phylogenetic groups B1, B2, A and D was 9.4%, 10.9%, 57.8% and 21.9%, respectively. Nineteen virulence-related genes were detected by PCR assay; ompA, fimH, vat, traT and iutA were highly prevalent. Virulence-related genes were remarkably more prevalent in group B2 than in groups A, B1 and D; notably, usp, cnf1, hlyD, papA and ibeA were only found in group B2 strains. Genotyping analysis was performed and four clusters of strains (named I to IV) were identified. Cluster IV contained all isolates from group B2 and Cluster IV isolates had the strongest pathogenicity in a mouse infection model. As phylogenetic group B2 and D ExPEC isolates are generally considered virulent, multilocus sequence typing (MLST) analysis was performed for these isolates to further investigate genetic relationships. Two novel sequence types, ST5170 and ST5171, were discovered. Among the nine clonal complexes identified among our group B2 and D isolates, CC12 and CC95 have been indicated to have high zoonotic pathogenicity. The distinction between group B2 and non-B2 isolates in virulence and genotype accorded with MLST analysis.ConclusionThis study reveals significant genetic diversity among ExPEC isolates and helps us to better understand their pathogenesis. Importantly, our data suggest group B2 (Cluster IV) strains have the highest risk of causing animal disease and illustrate the correlation between genotype and virulence.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-017-0975-x) contains supplementary material, which is available to authorized users.

Streptococcus suis is an important swine pathogen that can cause a variety of diseases. Streptococcus suis serotype 9 (SS9) is a prevalent serotype, but limited information is available. Here, we studied and compared 30 SS9 isolates, including 24 isolates from China between year 2004 and 2013, 5 isolates from Vietnam and a serotype reference isolate from Denmark. A multilocus sequence typing (MLST) analysis was performed to exploit the genetic relationships between those isolates. The phylogenetic tree based on the MLST data divides those isolates into two clades (I and II), revealing different evolutionary paths of collected strains. A virulence genotyping analysis was performed by detecting 23 virulence-related genes; the clustering result also revealed two clusters (I and II), highly in accordance with MLST analysis result, showing that phylogenetic relatedness led to the presence of similar virulence genotypes. Murine model infection experiment was performed to assess the virulence of those strains in cluster I and cluster II, which displayed high virulence diversity even within a same cluster/ST. Notably, ST 243 could be regarded as an ST with high virulence potential in SS9. In conclusion, this study has revealed high genetic and virulence diversity in SS9 isolates.

Aim: To develop a markerless gene deletion strategy in Streptococcus suis to solve the problem that several serotypes against electrotransformation of foreign DNA. Materials & methods: Bioinformatics retrieval was performed to identified ComRS systems functioning for natural transformation. A sacB-spc cassette with the upper and lower homologous fragments was amplification by fusion-PCR for spectinomycin-positive and sucrose-negative selection during gene deletion. Results & conclusion: Three phylogenetic clusters of ComR were identified to function for natural transformation by specific recognition to competence pheromone in S. suis. Thus, they were employed to establish gene deletion method. Its efficiency for genetic replacement was dependent on the length of homologs fragment and the concentration of donor DNA. This rapid gene-editing technique may greatly facilitate molecular studies on S. suis.