| Streptococcus suis(S.suis)is a widely distributed zoonotic disease of pigs with a variety of serious outcomes like meningitis,arthritis,septicemia,and endocarditis.This disease has great influence on the development of pig industry and human health.It has 35 serotypes,of which type 2(S.Suis 2)has the highest incidence rate and has been designed as the second category of animal diseases.However,some Tibetan pigs in Nyingchi area of Tibet appeared with clinical symptoms similar to S.Suis in recent clinical practices.Therefore,we developed the serological investigation of S.Suis 2 for Tibetan pigs in Nyingchi,in order to provide basis for carrying out follow-up epidemic prevention work and control measures.Enterococcus are conditional pathogens,widely distributed in nature and do not cause diseases generally.But the resistance of Enterococcus to available antibiotics has gradually acquired due to the extensive application of antimicrobial agents in recent years.This practice has caused an important attention in the world.Enterococcus microbial resistance in China has also increasingly enhanced,not only for aminoglycoside resistance,but β-lactam,macrolides,tetracycline and glycopeptide antibiotics,also showed high resistance rates.Besides,the diseases caused by Enterococcus also increased.However,the separation of enterococci is an essential step for the study of the resistance although it is difficult to distinguish from other cocci.Besides the importance of this bacterium,limited studies are available regarding enterococci in Tibetan pigs from different regions in this plateau.Therefore,the current study has isolated and determined the microbial resistance of enterococci.In this study,438 serum samples of pigs from Nyingchi area were detected by ELISA from December of 2014 to January of 2015,which investigated preliminarily the positive rate of S.suis 2 in the area and had an important public health significance for the prevention and control of the disease.Besides,enterococci isolates collected from July to September of 2015 and from June to August 2016 in Nyingchi were tested by K-B experiment and MIC.Based on this,the strains with strong resistance were screened and detected for the resistance genes.The results were as follows: 1.The seroprevalence of S.suis 2For present study,all 438 samples were examined by ELISA.The result showed that the antibodies against S.suis in 263 samples(60.05%)were found positive with the distribution of 152 out of 246 serum samples(61.79%)in Nyingchi and 111 out of 192(57.81%)in Mainling county;The positive percentage of female and male pigs was 61.50% and 58.96%,respectively.The differences among different regions and two genders were not statistically significant(P≥0.05).A higher rate of S.suis 2 in Nyingchi area was shown in this study.Therefore,local residents should have stronger sense of prevention and control for this disease.2.The results of the isolation for enterococciIn this study,trypticase soy agar(TSA)containing 50μg/ml Aztreonam,10μg/ml Polymyxin B Sulfate and 2% rabbit serum was used repeatedly to select suspicious colonies,and then Catalase test was selected to complete the initial identification of enterococci.And finally,16 Sr DNA sequencing and the conserved special tuf gene were both performed by PCR to determine the isolates.the following were the results: 51 strains from Tibetan pigs were recovered from 105 samples(48.6%)in 2015: 15 Enterococcus faecalis(29.4%),4 Enterococcus faecium(7.8%),27 Enterococcus hirae(52.9%),2 Enterococcus durans(3.9%)and 3 other enterococci strains(5.9%),and Enterococcus durans was first obtained in Tibetan pigs.In 2016,45 strains were isolated from 120 samples(37.5%)including 12 Enterococcus faecalis(26.7%),6 Enterococcus faecium(13.3%)and 27 other strains(60%).3.Test for antimicrobial resistanceK-B susceptibility test and minimum inhibitory concentration(MIC)were used to determine the susceptibility of 10 antimicrobial agents in this study.We found that all isolates had high resistant percentage to high-level kanamycin,gentamicin and streptomycin(60%-80%)and none was resistant to vancomycin,but the incidences of tetracycline and erythromycin for Enterococcus were approximately 50%.Compared to 2015,the resistance rate of ampicillin increased significantly in 2016.In addition,the vast majority of the strains were classified as multidrug resistant Enterococcus,especially Enterococcus faecalis,even up to 5 kinds of different antibiotics,6 resistant strains were not found.Therefore,Local residents should pay more attention to scientific medicine.4.Test for resistance genesBased on the results of K-B susceptibility test and MIC,10 resistant genes including aac(6’)-Ie-aph(2’)-Ia,aph(3’)-IIIa,aph(2’)-Ic,ant(4’)-Ia,ant(6’)-Ia,ant(3’)-(9),TEM,ermB,mef A,tetM were detected by PCR.The results showed that the resistance rates were not positively correlated with the resistance genes: 31 strains that were resistant to streptomycin at high level in this study in 2015 did not carry ant(6’)-Ia and ant(3’)-(9).Ant(3’)-(9),aph(2’)-Ic,(3’)-Ia,mef A,aph(3’)-IIIa and ant(6’)-Ia were not found although the positive rates of aac(6’)-Ie-aph(2’)-Ia,ant(4’)-Ia,ermB and tetM were all 100% in some strains in 2015.In 2016,3 and 6 strains carried with ant(6’)-Ia and ant(3’)-(9)respectively.However,ant(4’)-Ia was not found in all isolates.Besides,Enterococcus faecalis and Enterococcus faecium had higher resistance rates than other enterococci in 2015 and 2016,which reflected them a serious resistance. |
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