Molecular Epidemiology And Antibiotic Resistance Of Salmonella

Salmonella,the causative agent of salmonellos is in both humans and animals,is widely distributed,and makes serious threat to public health and safety.The drug resistance of Salmonella is becoming more and more serious,causing even a large number of extensively drug resistant isolates appear due to the prolonged and extensive use of antibiotics in human and animals.Plasmid,a self-replicated movable element,is widespread in Salmonella,and participate the horizontal transfer of resistance genes.Class Ⅰ integron,one of the most common types of integron in Gram-negative bacteria,has the function of capturing antibiotic resistance genes,and can promote the generation and spread of drug resistance.It is significant to study the distribution of plasmids and Class Ⅰ integrons in Salmonella,and explore the relationship between plasmids,class Ⅰ integrons and antibiotic resistance genes to prevent and control the outbreak of Salmonella.ObjectiveTo understand the prevalence of Salmonella in Jiangsu Province,and provide data support for studying the epidemiology and control measures of Salmonella;It is significant to understand the distribution of plasmids in Salmonella,and explore the relationship between the plasmid types,which could provide support date for monitoring the horizontal transfer of Salmonella antibiotic-resistant;Objective to analyze the class Ⅰ integron,antibiotic resistance genes and plasmid incompatibility groups,and to explore the acquisition of drug resistance of Salmonella.Methods1.268 Salmonella isolates from different sources were typed with serotypes and multi-site sequence typing(MLST).2.The incompatibility groups(Inc)of 206 Salmonella isolates were typed by 5 multiplex PCRs and 3 single PCRs,with total 18 pairs of primers.Polymerase Chain Reaction(PCR)was used to detect 12 antibiotic resistance genes:β-lactam resistance genes:blaTEM-1,blaCTX-M and blaOXA-1;sulfonamide resistance genes:sull and dfrA17;aminoglycoside resistance genes:aacC4 and aac(6)-1b;chloramphenicol resistance genes:floR;tetracycline resistance genes:tet(A)and tet(G);and quinolone resistance genes:qnrB and qnrS.3.The intI1 integrase gene of 206 Salmonella isolates was detected by polymerase chain reaction(PCR).Results1.A total of 19 serotypes and 26 sequence types(STs)were found.The most frequently observed clones in humans and animals(chickens and pigs)were S.Enteritidis(ST11),S.Typhimurium(ST19),and S.Derby(ST40).The most frequently clones in the chicken were S.Indiana(ST17)in recent years,it has not been prevalent on a large scale in Jiangsu Province.There was a corresponding relationship between sequence type and serotype.S.Indiana,S.Choleraesuis and S.thompson correspond to ST17,ST68 and ST319,respectively.In ST19 clone and ST34 clone,S.Typhimurium was the most frequently observed serotype.In ST11,S.Enteritidis was the most frequently observed serotype.In ST40,S.Derby was the most frequently observed serotype.4 CCs(CC11,CC64,CC19 and CC68)were identified,CC11 was mainly from Xuzh ou,CC19 was mainly from Zhenjiang,and CC68 was mainly from Yangzhou.2.There were nine plasmid incompatibility groups(IncHI2,IncI1,IncN,IncFIIs,IncFrepB,IncFIB,IncA/C,IncHI1 and IncFIA)in 206 Salmonella isolates.IncFIIs(22.82%),IncHI2(19.90%)and IncN(18.93%)were the major groups.The types of plasmids carried by Salmonella from animals were more than that from humans,IncFⅡs was ubiquitous in humans and animals,and IncHI2 and IncN were mainly found in chickens.It was found that IncHI2(59.09%)and IncN(61.36%)were mainly distributed in S.Indiana.The carrier rates of blaCTX-M(84.09%),blaOXA-1(77.27%),blaTEM-1(72.73%),sul1(81.82%),aacC4(88.64%),aac(6)-1b(81.2%),floR(81.82%)and dfrA17(61.36%)in S.Indiana were higher than those of other serotypes.Based on the carrying of antibiotic resistant genes and the typing of plasmids,all the isolates which carrying IncHI2 or IncN plasmids frequently contained blaTEM-1,blaC TX-M,blaOXA-1,sul1,aacC4,aac(6)-1band floR antibiotic resistance genes.3.The total positive rate of class Ⅰ integron was 25.24%.The positive rate of class Ⅰ integron in S.Indiana was 63.64%.The positive rates of class Ⅰ integron from chicken,pig and human were 59.62%,17.31%and 15.38%,respectively.The carryin g rate of blaCTX-M,blaOXA-1,sul1,aacC4,aac6-1b,dfrA17 and floR antibiotic resi stance genes in class Ⅰ integron positive isolates was significantly higher than that in class Ⅰ integron negative isolates.The positive rate of class Ⅰ integron in isolates containing plasmids(39.60%)was higher than that in isolates without plasmids(11.43%).The positive rate of class Ⅰ integrons in isolates containing IncHI2 or IncN plasmids(75.00%)was higher than that in isolates containing IncFIIs plasmids(4.25%).Conclusion1.The similarity of the genetic clones of animal and human isolates indicates a common ancestor,and reveals animals were a major source of Salmonella.S.Indiana(ST 17)was an emerging clone carried by chickens.Sequence types were related to serotypes and had higher discrimination,which can provide guidance and help for serotype identification.The results of MLST analysis showed that the Salemonlla homologous complex evolved from a single clonal ancestor,which had a unique regional distribution,and could evolve and vary in the process of transmission.2.The distribution of incompatibility groups from different sources and serotypes was different.The prolonged and extensive use of antibiotics in animals promoted the production and evolution of plasmids.IncFIIs could be transmitted horizontally in animals and humans,IncHI2 and IncN were mainly transmitted horizontally between chickens,and these two plasmids were more restricted by the serotype of S.Indiana.The mechanism of antibiotic resistance included the existence of specific antibiotic resistance genes.blaCTX-M,blaOXA-1,blaTEM-1,sul1,aacC4,aac(6)-1b and floR antibiotic resistance genes existed on IncHI2 or IncN plasmids,S.Indiana contained this characteristic plasmid,which moved horizontally between these serotypes,spreading drug resistance.3.Class Ⅰ integron was mainly distributed in S.Indiana.Class Ⅰ integron capture d antibiotic resistance genes of blaCTX-M,blaOXA-1,sull,aacC4,aac(6)-1b,dfrA17 and floR.IncHI2 or IncN plasmid was the main carrier of class Ⅰ integron.The class Ⅰ integron has the ability to capture antibiotic resistance gene.The uni queintegrons and multiple resistance genes co-located on the IncHI2 or IncN plasmid contributed to the dissemination of resistance,S.Indiana(ST 17)contains plasmids with this characteristic,which is the root cause of the emergence and spread of resistance.