| Sichuan is the historical main epidemic area of Streptococcus suis.In 2005,there was a report of this bacterium infecting people on a large scale,and it is also the main pathogenic bacterium that has endangered the development of the pig industry in this area in recent years.In order to investigate the prevalent serotypes of Streptococcus suis in this area,and to explore the drug resistance and dominant virulence genotypes of Streptococcus suis in this area,we conducted a study on the lung tissue of the fattening pigs that died in some areas of Sichuan from 2021 to 2022.The isolation and identification of the main biological characteristics of the study.The results of the study are as follows:A total of 151 diseased lung samples of dead fattening pigs in the region were collected from 2021 to 2022,and 32 strains of Streptococcus suis were isolated using TSA medium.Using the typing primers,10 strains（10/32）of serotype 16,7 strains（7/32）of type 2,3strains of type 9（3/32）,1 strain of type 7（1/32）,4 strains of type 7（1/32）were obtained.1strain（1/32）of type 30,1 strain of type 30（1/32）,1 strain of type 1（1/32）,1 strain of type5（1/32）,and 7 strains（7/32）.The above results show that the predominant serotype of Streptococcus suis in the region from 2021 to 2022 is type 16.In order to study the dominant virulence genotypes of Streptococcus suis in this region,we used specific primers to detect the distribution of the main virulence factors of SS,including hemolysin gene（sly）and lysozyme release-related protein gene（mrp）,by PCR method.,extracellular factor gene（epf）,virulence-related sequence（orf2）,and fibronectinogen binding protein（fbps）.The results showed that sly had the highest detection rate（13/23）.The sly,mrp and epf genes were used as virulence markers for typing research,and a total of 5 virulence genotypes were detected,namely sly+mrp-epf-（11/23）,sly+mrp+epf+（1/23）,sly-mrp-epf-（8/23）,sly-mrp+epf+（1/23）,sly+mrp+epf-（2/23）,the dominant virulence genotype was sly+mrp-epf-.The drug susceptibility test was carried out on the 24 isolated Streptococcus suis strains using the KB disc method,among which the resistance to lincomycin was the highest（24/24）,followed by oxycytosine（23/24）,g Linomycin was（22/24）,florfenicol was（22/24）,and the resistance to cefpirome was the lowest（9/24）.The analysis of the drug susceptibility test results showed that from 2021 to2022,the resistance of Streptococcus suis to lincosamides,oxazolidinone,and macrolides was serious,and cephalosporins were resistant to lower.It shows that cephalosporin antibiotics can play a good clinical effect on Streptococcus suis in this area.In order to further understand the distribution of drug resistance genes of the strains,whole genome sequencing of two serotype 16 SS11 and SS22 strains with high drug resistance in the drug susceptibility test was performed by high-throughput sequencing technology.The full gene length of SS11 strain was 2183722 bp,the number of coding genes was 2178,and the GC content was 41.08%.And predicted 9 gene islands and 5 prophages.The full gene length of SS22 strain was 2186009 bp,the number of coding genes was 2230,and the GC content was 41.1%.At the same time,7 gene islands and 5 prophages were predicted.The results of gene function annotation showed that SS11 and SS22 had the strongest ability to transport carbohydrates,which was the basis for the rapid spread of bacteria.The coding sequence was annotated for drug resistance genes,SS11 and SS22 were predicted to have 12 and 10 drug resistance genes through ARDB database,10 and 21 drug resistance genes were predicted through CARD database,and vga E was predicted for the first time in Streptococcus suis,Yaj C,van RM and gol S genes.By comparing the drug-resistant genotype and drug-resistant phenotype,the drug-resistant phenotype and drug-resistant genotype maintained a high consistency.Conjugation experiments were performed on the predicted lsa（E）and optr A genes.When linezolid was used as the drug of choice,the conjugation efficiencies of SS11,SS22 and Staphylococcus aureus were 4.3x10-7 and6.2x10-6.;When lincomycin was selected as the drug,the conjugation efficiency of SS11,SS22 and Staphylococcus aureus were 3.2x10-6 and 8.1x10-7in turn.On the one hand,the results of the conjugation experiment verified the existence of lsa（E）and optr A,and on the other hand,it indicated that Streptococcus suis and Staphylococcus aureus may have certain horizontal transfer ability. |
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