| Salmonella is an important zoonotic and food-borne pathogen,which seriously endangers the life and health of human,livestock and poultry.The irregular use and abuse of drugs in clinical treatment and livestock and poultry production result in the resistance of bacteria to one or more drugs.The emergence of drug-resistant bacteria leads to the reduction or even complete loss of drug treatment effect,which increases the difficulty of prevention and control of pathogenic bacteria.The multidrug resistance of Salmonella to drugs is becoming more and more serious,which poses a serious threat to food safety and public health and the healthy development of animal husbandry.Strengthening the surveillance and epidemiological investigation of antimicrobial resistance（AMR）of Salmonella is of great significance for the research and control of antimicrobial resistance of Salmonella transmitted from food chain to human.In this study,158 strains belonging to 30 serotypes of Salmonella isolated from 9provinces in China were investigated,including 24 from patients,12 from livestock and 122 from poultry.Firstly,the drug resistance gene spectrum of Salmonella was studied based on the whole genome sequencing（WGS）technology,and then the drug susceptibility test was used to study the drug resistance phenotype spectrum of Salmonella,and the correlation between the drug resistance gene spectrum and phenotype spectrum was studied to provide technical support for the prevention and control of Salmonella.The main research results were as follows:1.Study on drug resistance gene profile of Salmonella based on whole gene sequence.A total of 158 strains of Salmonella genome DNA were extracted,and 97drug-resistant genes were identified by whole-genome high-throughput sequencing,genome sequence splicing,and drug-resistant gene identification and annotation.The detection rate of each drug-resistant gene was different（0.63%-100%）.（1）A total of23 aminoglycoside resistance genes were detected,of which aac（6’）-Iy had the highest detection rate（62.03%）,followed by aac（6’）-Iaa（37.97%）.（2）A total of 11 quinolone resistance genes were detected,among which gyr A p.S83F/N87G（20.89%）and gyr A p.D87G（18.35%）had the highest detection rates.Amino acid sequence comparison showed that 63 strains had mutations in gyr A and par C genes.Gyr A had two amino acid mutations（Asp87Gly and Ser83Phe+Asn87Gly）and Par C had one amino acid mutation（Ser57Thr+Thr80Ser）.（3）Sevenβ-lactam resistance genes were detected,among which bla TEM-1（33.54%）and bla OXA-33（15.19%）had the highest detection rates.（4）sul1（28.48%）,dfr A17（13.29%）,tet（B）（10.76%）,mph A（7.59%）and cat B3（15.19%）had the highest detection rates of sulfanilamide,trimethoprene,tetracycline,macrolide and chloramphenicol resistance genes,respectively.The relationship between drug resistance genes of Salmonella and serotype and SNP was analyzed.The results showed that the number of drug resistance genes carried by S.Indiana strain was significantly higher than that of other serotypes,followed by S.I 4,[5],12:i:-,S.Meleagridis,S.Thompson and S.Typhimurium.The closely related strains showed similar gene profiles of drug resistance.2.Study on Salmonella drug resistance profile based on drug sensitivity test.The drug sensitivity test of 10 commonly used drugs was carried out by Kirby Bauer paper diffusion method.（1）The results showed that Salmonella had the highest resistance to ceftazidime（92.41%,n=146）,timicoxin（85.44%,n=135）and sulfamethoxazole（84.81%,n=134）.It was followed by ampicillin（44.94%,n=71）and chloramphenicol（29.75%,n=47）,with the lowest level of resistance to imipenem（5.70%,n=9）.（2）A total of 158 strains showed 51 drug resistance profiles,the multidrug resistance rate was 82.28%,and 41 strains showed CAZ-SMZ-TIL drug resistance profiles.（3）The correlation of resistance phenotype with serotype and host origin was analyzed.S.Indiana strain had the widest drug resistance spectrum and was resistant to more than 6 antibiotics,followed by S.I 4,[5],12:i:-,S.Meleagridis,S.Thompson and S.Typhimurium.The drug resistance of poultry and domestic animal isolates was generally higher than that of human isolates.The closely related strains showed similar resistance profiles.3.Study on correlation between drug resistance genotypes and phenotypes of Salmonella.The sensitivity,specificity,positive predictive value and negative predictive value between the resistance genotype and the resistance phenotype were calculated.GEN（100%）,KAN（100%）,AMP（98.59%）,ENR（94.12%）,IPM（88.89%）,FFC（80.00%）and CHL（78.72%）showed high sensitivity to phenotypic resistance.AMP（100%）,TIL（100%）,SMZ（94.87%）,CAZ（94.29%）,CHL（92.50%）and FFC（70.00%）had high positive predictive value of phenotypic resistance.The sensitivity,specificity,negative predictive value and positive predictive value of quinolone resistance genes were higher in the strain carrying both QRDR mutation and PMQR than in the strain carrying only one of the genes.Strains carrying the chloramphenicol resistance gene cat II developed resistance to chloramphenicol,but did not have phenotypic resistance to chloramphenicol FFC.The correlation between drug resistance genotype and host source and serotype is consistent with the correlation between drug resistance phenotype and host source and serotype.There was an obvious correlation between the number of resistance genes and the drug resistance profile of Salmonella. |
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