| Streptococcus suis is considered to be a major pathogen in the swine industry which leads to sepsis,meningitis,arthritis,acute pneumonia and death.It is also an important zoonotic agent for human.Based on the different capsular polysaccharide antigen,S.suis can be divided into 33 serotypes,but some strains cannot be stereotyped.Serotypes 1-9,14 and 16 can infect pigs and cause swine disease.S.suis serotype 2(SS2)is the most virulent and prevalent;it is the mainly pathogenic serotypes for both pigs and human.The positive rate of healthy pigs carrying S.suis is significantly high with complex serotypes.So these healthy pigs become potential source of infection.Monitoring healthy pigs carrying bacteria is a useful method for S.suis epidemiological survey.In this study,we monitored the presence of S.suis in healthy pigs from two farms in southern Jiangsu and explored the possibility of treatment using Nisin after S.suis infection,which will provide prevention and control strategies for S.suis disease in the region.Two farms,YK and KL,in southern Jiangsu province were selected.Twenty healthy pigs were randomly selected in every 5 different groups,including sows,20-days-old piglets,40-days-old pigs,60-days-old pigs as well as 120-days-old pigs.The nasal swab samples were collected in March,June,September and December in 2015.Bacteria species and serotypes were identified by PCR assay on the basis of house-keeping gene gdh,CPS1,CPS2,CPS7 and CPS9.The results were as followed:there were 400 healthy pigs nasal swab samples collected from YK farm in 2015.277 samples were gdh positive and the detection rate was 69.25%.Eleven strains of S.suis type 1(14),15 strains of S.suis type 2(1/2),20 strains of S.suis type 7,58 strains of S.suis type 9 were detected.The detection rates were 2.75%,3.75%,5%and 14.50%,repectively.In the second quarter of the year the infection rate(84%)was the highest in YK farm.The infection rate of sows and 20-days-old pigs(90%and 80%,respectively)was significantly higher than other ages groups;there were 400 healthy pigs nasal swab samples collected from KL farm in 2015,of which 232 parts were gdh positive,and the detection rate was 58%.Four strains of S.suis type 1(14),16 strains of S.suis type 2(1/2),21 strains of S.suis type 7,32 strains of S.suis type 9 were detected,and the detection rate were 1%,4%,5.25%and 8%,repectively.Similar to the YK farm,S.suisthe detection rate of type 9 was the highest(8%).The infection rate of sows and 20 days-old pigs(71.25%and 90%,respectively)was significantly higher than other ages groups.DNA template of sows and 20-days-old pigs in the second and third quarter in 2015 were choosed,and serotypes were identified by PCR assay on the basis of specific gene sequences of 33 serotypes.The results were as followed:22 kinds of serotypes were found in the 80 nasal swab samples in YK farm,and serotype 4(46.25%),serotype 9(37.5%),serotype 21(37.5%)were the dominant serotype;20 kinds of serotypes were found in the 80 nasal swab samples in KL farm,and serotype 29(62.5%),serotype 9(31.25%),and serotype 4(25%)were the dominant serotype.The species and dominant serotypes overlapped in the two farms.There were 17 kinds of S.suis serotypes simultaneously detected in the two farms,respectively,serotype 2(1/2),serotype 3,serotype 4,serotype 5,serotype7,serotype8,serotype 9,serotype 11,serotype 12,serotype 13,serotype 15,serotype 16,serotype 18,serotype 21,serotype 28,serotype 29 and serotype 31.Multiple serotypes were popular and the proportion of two or above two serotypes mixed was more than 70%.Samples with mixed serotypes mostly concentrated in the 2-5 kinds of serotypes,but up to 9 serotypes in YK farm and 11 serotypes in KL farm.Single colony from nasal swabs of sows and 20-days-old pigs in YK and KL farm in the second quarter of 2015 was isolated,and then a serotype 4 strain SS4 and a serotype 31 strain SS31 which had relatively higher detection rate in YK farm were selected as well as serotype 2 virulent reference strain SS2-1.We detected minimum inhibitory concentration(MIC)of each for bacteriocin Nisin and explored the possibility of treatment using Nisin after S.suis infection.The results were as followed:there were 35 strains obtained from 21 nasal swabs samples in YK farm,including 1 strain of serotype 2,1 strain of serotype 3,8 strains of serotype 4,1 strain of serotype 15,4 strains of serotype 16,1 strain of serotype 18,9 strains of serotype 21,3 strains of serotype 28,and 7 strains of serotype 31;there were 39 strains obtained from 22 nasal swabs samples in KL farm,including 1 strain of serotype 9,3 strains of serotype 11,3 strains of serotype 16,1 strain of serotype 21,1 strain of serotype 28,29 strains of serotype 29 and 1 strain of serotype 31.The MIC of Nisin toward SS2-1,SS4 and SS31 were 10?g/mL,20?g/mL and 40?g/mL,respectively.In vivo analysis showed that Nisin can be used to treat S.suis infection. |
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