Epidemiological Survey Of Streptococcus Suis Of Guangxi In 2018

Streptococcus suis is a kind of Gram-positive bacteria with capsule.It usually causes arthritis,meningitis and local lymph node suppurative symptoms in pigs,and even leads to dangerous toxic shock,which seriously damages the health and safety of breeding animals and human beings,and brings incalculable property loss to the breeding industry.Streptococcus suis is widely distributed in nature.Its infection sites are digestive tract,reproductive tract and upper respiratory tract of pigs.Pigs of all ages can be infected.In this study,the incidence and prevalence of Streptococcus suis in Guangxi were investigated and analyzed in order to further understand the epidemic law of the disease and provide the basis for controlling and preventing the spread of the disease in the region.In order to investigate the incidence and prevalence of Streptococcus suis in Guangxi,and determine the proportion of different serotypes in each region,559 pig tissue samples from 8 cities and counties in Guangxi Zhuang Autonomous Region were collected in 2018.The selected medium was used to isolate and identify Streptococcus suis in the disease materials.A total of 214strains(38.28%)of Streptococcus suis were isolated.The positive rate of Streptococcus suis in Napo County was 69%,which was the highest in several areas.The lowest positive rate was 5% in Bobai County and 6% in Dongxing City.The remaining areas are Liuzhou 46%,Lingshan 56%,Yulin 40%,Longzhou 37% and Daxin 45%.Compared with 2017,the total isolation rate of Streptococcus suis in Guangxi decreased slightly from 38.9% to 38.3% in 2018,and the isolation rate of Dongxing City decreased from 18% to 7%,with a significant change.Subsequently,all Streptococcus suis strains in 2018 were serotyped.Among 214 strains of Streptococcus suis,20 strains(9.35%)were serotype 2,8(3.73%)were serotype 3,7(3.27%)were serotype 4,8(3.73%)were serotype 5,2(0.93%)were serotype 7,2(0.93%)were serotype 8,22(10.28%)were serotype 9,1(0.46%)serotype 10,5(2.33%)serotype 11 and 2(0.93%)serotype 12 There were 3 strains of serotype 13(1.40%),17 strains of serotype 15(7.94%),3 strains of serotype 19(1.40%),3 strains of serotype 20(1.40%),6 strains of serotype 21(2.80%),1 strain of serotype 25(0.46%),1strain of serotype 26(0.46%),2 strains of serotype 27(0.93%),3 strains of serotype 29(1.40%),4 strains of serotype 30(1.87%),19 strains of serotype 31(8.8)8%)。Therefore,the predominant serotypes of Streptococcus suis in Guangxi in 2018 were serotypes 2,9,15 and 31.In order to investigate the virulence of 214 strains of Streptococcus suis and determine the distribution of virulence genes in different regions and serotypes,PCR was used to detect the virulence genes.The results showed that 90 strains(42.05%)with sly gene,22 strains(10.28%)with MRP gene,61 strains(28.50%)with EF gene,152 strains(71.02%)with ORF2 Gene.It is suggested that the sequence of virulence gene carrying rate of Streptococcus suis in Guangxi in2018 is ORF2 > sly > EF > MRP.In order to study the drug resistance of Streptococcus suis in Guangxi in2018,30 strains of Streptococcus suis were randomly selected and the drug sensitivity of 35 common antibiotics was determined by disk diffusion method.Twenty five strains were not sensitive to antibiotics.Most Streptococcus suis in Guangxi were not sensitive to aztreonam,penicillin and tetracycline,but sensitive to erythromycin and cotrimoxazole.Finally,in order to screen out highly virulent Streptococcus suis strains,this study used zebrafish as animal model,and randomly selected 91 strains of Streptococcus suis isolated in 2018 for virulence test.Among them,8 strains had strong virulence,accounting for 8.8%.The virulent strains were mainly serotypes 2 and 9 in Daxin,Lingshan and Liuzhou.No identical virulence factors were found among the 8 virulent strains.The results showed that the isolation rate of Streptococcus suis in Guangxi in 2018 was almost unchanged compared with that of last year,but there were significant differences in the isolation rate among different regions,and the proportion of serotypes was also different.The isolation rate of Streptococcus suis in Daxin County,Lingshan County and Liuzhou city was higher than the average level in Guangxi Province,and strong strains were isolated from all of them.This study confirmed the complexity of the local epidemic situation of Streptococcus suis,and provided data support for understanding the development law of Streptococcus suis disease and its prevention and control in Guangxi.