Comparative analysis of whole genome structure of Streptococcus suis using whole genome PCR scanning

An outbreak associated with Streptococcus suis infection in humans emerged in Sichuan province, China in 2005. The outbreak is atypical for the apparent large number of human cases, high fatality rate and geographical spread. To determine whether the bacterium has changed, we compared both human and animal isolates from the Sichuan outbreak with those collected previously within China and in other countries using whole genome PCR scanning (WGPScaning) comparative sequencing of several known virulence factor genes and multilocus sequence typing (MLST) analysis. WGPScanning analysis showed that all primer pairs yielded PCR products of the expected sizes in all four strains tested. The nucleotide sequences of all the detected virulence factor genes are identical in the four strains and MLST results showed that the four isolates studied and reference strain all belonged to the ST1 com-plex. No new genetic changes were found in the genome structure of the isolates from this Sichuan outbreak.

Genetic diversity of Listeria monocytogenes isolates from farm products in Shanghai,China

Farm products are considered important vehicles for the transmission of Listeria monocytogenes(L.monocytogenes).The typing of L.monocytogenes from farm products contributes to the surveillance and source tracing of the pathogen.In this study,77 L.monocytogenes strains from seven farm product categories in Shanghai were analyzed by serological typing,multilocus sequence typing(MLST),pulsed-field gel electrophoresis(PFGE),and whole-genome nucleotide polymorphism(wgSNP).The results showed that the 77 isolates were classified into four serovars(1/2a,1/2c,1/2b,and 4b),and of these,1/2a(n=47)was the most prevalent.Seventeen sequence types(STs)were generated by MLST with two novel STs(ST1402 and ST1403),and 20 of 77 L.monocytogenes isolates had high genetic identity with previously documented outbreak isolates according to the minimum spanning tree from the MLST results.Moreover,34 PFGE patterns(PF1-PF34)were differentiated,and based on a similarity value higher than 80%by the unweighted pair group method dendrogram,the discriminatory index was relatively low(equal to 0.775).Furthermore,14 isolates were chosen and further analyzed by wgsNP based on the previous typing results,which demonstrated that wgSNP and MLST yielded mostly consistent typing results but higher resolution than PFGE.In conclusion,77 L.monocytogenes isolates from farm products collected in nine districts in Shanghai were highly genetically diverse,and 20 of these isolates had high relatedness with previously documented outbreak strains worldwide.The results indicate a possible cross-contamination risk of L.monocytogenes and a potential public health concern resulting from farm products during the supply chain in Shanghai,China.