Study On The Correlation Between Virulence Genes And Pathogenicity Of Chicken Pathogenic Salmonella

Salmonella is an important pathogen of zoonosis with a wide range of hosts.In recent years,the widespread use and even abuse of antibiotics in clinical practice result in more and more serious problem of antimicrobial resistance.Salmonella can invade the host,reproduce and cause illness,which is closely related to its virulence genes.In this study,chicken pathogenic Salmonella was indentified and characterized,the antimicrobial resistance and pathogenicity were determined,the resistance genes and virulence genes were detected,the relationship between antimicrobial resistance gene and resistance phenotype,virulence genes and pathogenicity were analyzed,to provide scientific basis for the prevention and treatment of salmonellosis.Tissues were collected from suspected chicken and enhanced Salmonella by SC enrichment liquid.Salmonella was isolated and cultured by XLD agar plate.Single colonies of pure culture were selected for biochemical,serological and PCR identification.As a result,a total of 55 Salmonella isolates belonging to 4 serotypes were acquired,of which 6 isolates belonged to group A,23 isolates to group B,1 isolate to group C and 25 isolates to group D.Among them,group D accounted for about 45%,which is the dominant group of Salmonella.The susceptibility to 18 kinds of antimicrobial drugs of 55 Salmonella isolates was determined by K-B agar method which was recommended by CSLI.The results showed that,of all the 55 Salmonella isolates,100%isolates were resistant to rifampicin,amoxicillin,penicillin C,oxacillin and cefalotin;more than 90%isolates were resistant to erythromycin,lincomycin,polymyxin B,cotrimoxazole,nitrofurantoin;from 50%to 90%isolates were resistant to doxycycline,streptomycin and norfloxacin;and 7.27%,3.64%isolates were resistant to entamicin and spectinomycin,respectively.Sixteen kinds of antimicrobial resistance genes,including blaTEM,blaPSE,blaCMY,aadAl,Aph(3)-IIa,aadA2,tetB,tetG,tetM,text,Sull,Sul3,qnrA,qnrB,qepA and qnrS,were detected by PCR.The results showed that,of the 55 Salmonella isolates,25.45%contained three resistance genes,21.82%contained five resistance genes,21.82%contained two resistance genes,20.00%contained four resistance genes,3.64%contained one resistance gene and 1.82%contained seven resistance genes.Of all the resistance genes,tetX was the highest detected gene with 78.18%,while blaPSE,Aph(3)-?a,aadA2 and qnrA could not be detected.Thirty-one kinds of virulence genes,including plasmid virulence genes such as spvR?spvA?spvB?spvC?spvD and pathogenicity island virulence genes such as invH,sipA,sipB,sopA,sopD,avrA,hilA,iacP,prgK,ssaB,ssaQ,sifA,sseL,ssrA,ttrB,mgtC,misL,rmbA,rhuM,sugR,orf319,siiD(spi4D),siiE,spi4H,sopB,pipC and so on,were detected by PCR.The results showed that the plasmid virulence genes were detected in more than 60%of isolates;the pathogenicity island virulence gene ttrB and orf319 were the most common genes detected in more than 92.73%of isolates,while ssaQ and sifA genes were detected in less than 10%of isolates.The pathogenicity of 55 Salmonella isolates was determined by pathogenic experiment in mice.All isolates were pathogenic to mice,but the time and dose of death were different.Ten isolates were selected randomly to determine their median lethal dose(LD50),and it ranged from 3.18 × 1 08 cfu/mL to 4 × 107 cfu/mL.Overall,the study indicated that 55 pathogenic Salmonella isolates were isolated and identified from chicken,and the proportion of D group serotype was about 45%,showing that it was the dominant group.Salmonella isolates were commonly resistant to antimicrobial drugs and multiple drug resistances were very serious.All the Salmonella isolates were pathogenic to mice.There was a positive correlation between resistance phenotype and resistance genes,and also between pathogenicity and virulence genes.