Epidemiological Characteristics And Drug Resistance Characteristics Of Salmonella Strains Isolated From Ducks

There are more than 3000 serotypes,which are important pathogens that endanger human and livestock health.Salmonella disease is the general name of various animal diseases caused by Salmonella.Salmonella can be mixed with other pathogens to infect humans and animals,causing huge economic losses to the breeding industry.Especially for large-scale duck farms,Salmonella can spread rapidly once it breaks out,leading to mass deaths of ducklings.With the widespread use of antibiotics,Salmonella has become more resistant to antibiotics and increased the emergence of multi-resistant Salmonella,posing a great threat to the duck breeding industry.The aim of this study was to investigate the prevalence and characterization of Salmonella in duck farms and slaughterhouses in this region.From December 2016 to April2017,a total of 2342 samples were collected from duck farms and a slaughterhouse in Taian and Jinan,Shandong Province.Salmonella were isolated and identified by medium and PCR.Then,the Salmonella serotype was determined by plate agglutination test,and the Salmonella gene sequence was determined by multilocus sequence typing?MLST?and pulse-field gel electrophoresis?PFGE?.The classification method was used to analyze the classification characteristics of Salmonella and the genetic relationship between them.Using PCR technology to detect 13 common virulence genes,25 drug resistance genes and class I integrants to understand the characteristics of virulence genes and drug resistance and the presence of gene cassettes of Salmonella.The drug sensitivity test was used to detect the drug resistance of 14 commonly used drugs,and the drug resistance of Salmonella in the region was preliminarily understood,which provide a theoretical basis for rational drug use in production.A total of 49 duck Salmonella strains were collected and divided into 6 serotypes in the study.The most popular serotype was Salmonella enteritidis?40.8%?,followed by S.Anatum?20.4%?,S.Typhimurium?16.33%?,S.Kentucky?10.20%?,S.Indiana?10.20%?and S.Montevideo?2.04%?.Moreover,they were divided into seven ST types.The dominant ST is ST11?40.8%?,followed by ST2441?20.4%?,ST19?12.2%?,ST17?10.2%?,ST198?10.20%?,ST1544?4.08%?and ST305?2.04%?.Moreover,the49 Salmonella isolates are divided into 39 PFGE patterns,which grouped into ten clusters.S.Enteritidis and S.Anatum have high homology,most of which are located in the same cluster,indicating that S.Enteritidis and S.Anatum may be transmitted by Salmonella clones of the same clonal line.Comprehensive analysis of the three,serotyping and MLST typing ability is similar,while PFGE typing ability is stronger.Thirteen virulence genes were detected in the 49 Salmonella stains.The highest detection rates are invA?100%?,hilA?100%?and sipA?100%?virulence genes,followed by stnP1?91.8%?and ssrA?91.8%?virulence genes.And the lowest detection rates are ssaR?16.3%?and sopE?16.3%?virulence genes.Additionally,the detection rate of Salmonella virulence genes isolated from Farms 1 and a slaughterhouse is significantly lower.The antimicrobial sensitivity of 49 Salmonella to 14 antibiotics?9 antibiotics such as penicillins,cephalosporins and aminoglycosides?is detected by paper method.The results show that the highest resistance rate is erythromycin?100%?,followed by nalidixic acid?95.92%?,ampicillin?55.10%?and streptomycin?55.10%?.Among them,13 kinds of antibiotics detected different degrees of drug resistance,and only polymyxin B shows drug sensitivity.The resistance to S.Indiana in the study is particularly severe,resistant to 7-8antibiotics in 9 antibiotics and resistant to 12-13 antibiotics among 14 antibiotics.In addition,Salmonella isolates from Farm 1 and a slaughterhouse are obviously less resistant.Through the detection of 25 kinds of drug resistance genes,49 duck Salmonella stains were detected 11 kinds of drug resistance genes.Among them,the highest detection rate of drug resistance genes is bla_TEM,accounting for 73.47%(bla_TEM-1EM-1 accounts for 61.23%,bla_TEM-116EM-116 accounts for 10.20%and bla_TEM-181EM-181 accounts for 2.04%),followed by sul2?28.57%?.Tetracycline and chloramphenicol resistance genes are not detected.Moreover,9Salmonella stains are not detected,and 5 of them are from Farm 1.The Salmonella stains isolated from Farm 1 and a slaughterhouse are visibly less resistant.Among all of the 49Salmonella strains,17 strains were found to be carrying class?integrons,yielding at detection rate of 34.69%.And the drug resistance gene cassette is mainly aadA7+aac3-ld?1.5kb,n=15?.In addition,94.12%?16/17?of the Salmonella carrying the drug resistance gene cassette are multi-drug resistant Salmonella,and the resistance gene cassette carried by the class I integro may have a certain correlation with the resistance of Salmonella.This study analysis and researches the characteristics of Salmonella in duck farms and a slaughterhouse in this region from multiple aspects,and applied the three classification methods for the first time to explore the genetic relationship between different Salmonella species in different farms in Shandong province,which enriches the epidemiological data of Salmonella.At the time,it explored the characteristics of resistance of Salmonella,provided a theoretical basis for clinical drug use in breeding industry,and was helpful for the prevention and treatment of Salmonella.