Identification And Typing Of Salmonella Contamination And Analysis Of Resistance Genes In Fresh Animal Source Foods Marketed In Hubei Province

Salmonella is one of the major causes of food-borne diseases.In particular,animal meat products are an important route for the spread of Salmonella.Analyzing the distribution of Salmonella in the food production chain can provide theoretical guidance for the prevention and control of food-borne diseases caused by Salmonella infection.Analyzing the types,drug resistance and drug resistance genes of Salmonella in foods from different sources will help to understand the drug resistance of Salmonella and reveal the mechanism of the emergence and spread of Salmonella drug resistance.In this study,Salmonella was isolated and identified from fresh commercial animal foods in Hubei Province.Serotypes,molecular sequence types,antibiotic susceptibility,drug resistance gene types,class I integrons and ISCR1 elements were detected and analyzed.A preliminary analysis of Salmonella contamination and drug resistance in animal-source foods sold in Hubei Province was conducted.The main research contents and results are as follows:?1?Isolation and identification of Salmonella in commercial fresh raw foodsGB4789.4-2016 was used to isolate Salmonella in animal-derived foods.The isolates were serotyped by the slide agglutination method and the isolates were subjected to molecular typing using the MLST method.Twenty-seven Salmonella strains were isolated from 220 samples of animal origin.The prevalence of Salmonella in animal foods from Hubei Province was 12.3%?27/220?.Serotyping of 66 isolates of Salmonella showed that there were 19 serotypes and 1 rough type.The main serotypes were S.Thompson?18.2%,12/66?and S.Agona?13.6%,9/66?.).In the MLST classification,66 strains of Salmonella isolates were divided into 27 ST-types,of which the most ST-type were ST26?18.2%,12/66?and ST541?12.1%,8/66?.The study also found six new ST types.The results show that the MLST classification has higher discrimination,so the MLST classification method can better classify Salmonella subtypes.?2?Detection of resistance phenotypes and drug resistance genes of Salmonella isolatesSixteen Salmonella isolates were selected for K-B experiments using 14 antibiotic sheets from seven major antibiotics.Twenty-three of the six categories of drug resistance genes were selected and PCR-based methods were used to detect drug resistance genes of Salmonella isolates.The results showed that Salmonella isolates were resistant to sulfonamide complex and tetracycline?43.9%?.In addition,only S.Thompson isolates were found to have higher resistance to cefazolin?58.3%,7/12?.Corresponding to the sulforesin resistance gene sul1?38/66,57.6%?,?-lactamase resistance gene bla_TEM?32/66,48.5%?and tetracycline resistance gene tetA?26/66,39.4?%)is the dominant gene.The detection rates of class I integron and ISCR1 elements in 66 isolates of Salmonella were 27.3%?n=18?and 22.7%?n=15?,respectively.After comparison,it was found that class I integron and ISCR1 element positive strains showed resistance to more than three kinds of antibiotics.PCR amplification of the class I integron resistance gene cassette revealed that 13 out of 18 strains had an amplification band of about 150 bp in length and were empty gene cassettes.The other five PCR amplifications were 1.7kb?aacA4C?arr-3?dfr2,n=1?,2.2kb?dfrA12–orfF?aadA21,n=1?,0.9kb?aadA2,n=1??1.9kb?dfrA12–orfF?aadA2,n=1?,2.3kb?dfr17?aadA5,n=1?.PCR amplification of the ISCR1 resistance gene cassette showed that 7 out of 15positive strains amplified a 2.7 kb band.Sequence alignment results showed that there were two resistance genes in the seven gene cassettes,which were quinolone resistance genes qnrB1 and qnrB2,indicating that the ISCR1 element resistance gene cassette is closely related to the quinolone resistance gene qnrB.The isolate numbered 54 in this study contains both genetic elements of resistance gene cassettes,and the gene in its class I integron resistance gene cassette contains three major classes of drug resistance genes:aacA4C?arr-3?dfr2.There are reports of Salmonella class I integrants.After comparison,the isolate of Salmonella was found to be amoxicillin,ampicillin,chloramphenicol,streptomycin,and sulfonamide complexes.And tetracycline resistance,indicating that class I integrons and ISCR1 elements are closely linked to Salmonella multidrug resistance.