| Streptococcus suis disease is zoonotic,caused by a variety of pathogenic Streptococcus suis.After Streptococcus suis infects pigs,the sick pig often have related clinical symptoms such as meningitis,arthritis,pneumonia,etc.,which can eventually lead to death,bring great economic losses to the pig industry,and also bring great safety risks to front-line workers.Streptococcus vaccine used in veterinary clinic is mainly inactivated vaccine,but the effect is not ideal.At present,the treatment of streptococcus suis mainly depends on antibiotics.Under the pressure of selection of antibiotics,many streptococcus strains have developed different degrees of drug resistance.The research on drug resistance detection and transmission mechanism of Streptococcus suis will have important significance for guiding scientific clinical drug selection,improving the treatment effect of Streptococcus suis and controlling the transmission of drug resistance.The investigation of 15 pig farms in Shenyang showed that the incidence rate of suspected Streptococcus suis was from high to low: finishing pigs,nursing pigs,lactating piglets,sows,the incidence rates were 4.79%,4.04%,2.88% and 1.71% respectively.The incidence of disease in large-scale pig farms was 3.55%,lower than 4.96% in bulk pig farms.In this experiment,nasal swabs of sick pigs from different pig farms in Shenyang were collected and the suspected strains were identified by 16 S r RNA sequencing.A total of 22 strains of Streptococcus suis were identified,and the isolation rate of Streptococcus suis strains was 18.33%.The resistance of 24 kinds of veterinary antibiotics to Streptococcus suis was detected in this study.The results showed that the resistance of Streptococcus suis isolates to gentamicin was the most serious in shenyang area,and the resistance rate was 100%.The resistance rates of Streptococcus isolates to aminoglycosides,tetracyclines,macrolides,fluoroquinolones,β-lactams,chloramphenicol,lincomycin and polypeptide antibiotics were 63.64%-100%,77.27%-95.45%,59.09%-95.45%,81.82%-90.91%,68.18%-90.91%,81.82%,72.73% and 59.09% respectively.Streptococcus suis isolates were relatively sensitive to tylosin and bacitracin,and the sensitivity rate was 40.91%.All Streptococcus suis isolates were resistant to at least six antimicrobial agents,and three strains were resistant to the 24 antimicrobial agents.The encoding genes of class I integron and gene cassette of 22 Streptococcus suis strains were detected by PCR,and the drug resistance gene carrying status of the whole cassette and insertion region of the integrated cassette was analyzed.The results showed that the carrying rate of class I integron of 22 Streptococcus suis isolates was 95.45%(21/22).The carrying rate of gene cassettes in integron-positive strains was 95.24%(20/21),among which the arrangement of gene cassettes related to drug resistance was coding dihydrofolate reductase and aminoglycoside transferase dfr A1-aad A1,accounting for 20.0%(4/20)of gene cassette-positive strains,suggesting that it may be related to the drug resistance of four Streptococcus suis isolates to sulfonamides and aminoglycosides.This study shows that the incidence of Streptococcus suis is high in Shenyang,and the drug resistance of Streptococcus suis isolates is serious.It is suggested to use tylosin or bacitracin to treat Streptococcus suis in this area.The integron-gene cassette system may play a important role in the drug resistance transmission of Streptococcus suis in this area,but it can not completely explain all drug resistance phenotypes of Streptococcus suis,indicating that there are other drug resistance mechanisms to mediate the drug resistance of Streptococcus suis. |
