To investigate the prevalence and distribution of Salmonella and its serotypes in chickens in Hebei Province,and to analyze its pathogenicity,a total of 631 anal swabs and 62 diseased tissues were collected from 34 chicken farms in 7 regions of Hebei Province from 2018-2021,totaling 693 samples.The samples were inoculated into ordinary agar medium for isolation and purification of the pathogenic bacteria,followed by Gram staining and microscopy.The isolates were inoculated in different medium respectively,and the isolates were biochemically identified.PCR and sequencing of 16S rRNA gene were used to identify the isolates,and 32 sequencing sequences were randomly selected for sequence alignment by BLAST of NCBI,and the homology of the gene was analyzed by DNAStar software.The serogroups and serotypes of the isolates were identified by slide agglutination method,and the distribution of each serogroup and serotype in different regions of Hebei Province was counted.The results showed that 238 strains of Salmonella were isolated from 693 samples of diseased chickens.Except for 3 strains of undetermined group,the rest of the 238 isolates belonged to 6 serogroups A,B,C,D,E,and F,of which group D was at most 69.7%(166/238).The 238 strains of Salmonella were classed into 7 different serotypes and 1 undefined type,with the top three being Salmonella Pullorum(91/38.2%),Salmonella Paratyphi A(43/18.0%),Salmonella Gallinarum(40/16.8%).The statistical results of the distribution of serogroups and serotypes of isolates showed that except for the serogroup A circulating in Zhangjiakou area,the serogroups prevalent in other regions were all serogroup D.Salmonella Pullorum was the dominant serotype in Zhangjiakou area;There were 14 serotypes in Qinhuangdao,among which Salmonella Paratyphi A was its dominant serotype.The prevalent serotypes in Shijiazhuang,Chengde and Tangshan were all Salmonella Pullorum,and the serotypes dominant in Xingtai and Baoding were Salmonella Enteritidis and Salmonella Typhimurium,respectively.The susceptibility of 238 isolates to 22 drugs of 7 types of antibiotics was detected by K-B antimicrobial susceptibility paper method.PCR was used to detect the relevant drug resistance genes of the isolates,and the correlation between the drug resistance phenotypes and drug resistance genes was analyzed by the Fisher exact probability method in SPSS26.0 software.12 isolates of different serotypes were selected to infect chicks at dose of 0.2mL/chick(3×108cfu/mL),and the pathogenicity of each isolate to chicks was analyzed.The results of antimicrobial susce-ptibility test showed that the resistance strains of 238 isolates to oxacillin,erythromycin,penicillin,trimethoprim,ampicillin,and tetracycline were 97.5%(232/238),89.1%(212/238),78.6%(187/238),74.8%(178/238),74.4%(177/238),and 64.3%(153/238),respectively,and the resistance strains to other drugs were all below 32%,but all of them were sensitive to cephalosporin drugs.Most of the isolates were multi-drug resistant(58.4%,139/238),and the strains resistant to 6 drugs(32.8%,78/238)and 5 drugs(11.8%,28/238)were the most.The detection results of drug resistance gene showed that the detection rates of β-lactam resistance genes tem,sulfonamide resistance genes sul2,macrolide resistance genes erm(B)a,tetracycline resistance genes tetA and aminoglycoside resistance genes strA-B were 100%(238/238),75.2%(178/238),71%(169/238),65.6%(156/238)and 31.9%(76/238),respectively,and no quinolone and acyl alcohol resistance genes were detected.After analysis,the coincidence rates of aminoglycosides,tetracyclines,sulfonamides,β-lactams,and macrolide antibiotic resistance phenotypes and their drug resistance genes were 94.7%,98.1%,99.4%,97.5%,and 79.9%,respectively,showing strong correlations.The pathogenicity test results showed that all the 12 isolates could cause different clinical symptoms and necropsy lesions in the liver and intestine of infected chickens,and could cause different degrees of death in chickens,among which 10(100%)and 7(87%)chickens died,and the corresponding infectious bacteria were recovered from the liver of the dead chickens.The above results indicated that there were numerous serogroups and serotypes of 238 Salmonella strains isolated from different regions of Hebei Province in this study,and most isolates had strong resistance and exhibited multi-drug resistant,and the resistance genes of the five types of drugs carried by them were strongly correlated with their corresponding drug resistance phenotypes,and the isolates showed different pathogenicity to chicks.This study provides a reference for the epidemiological investigation of Salmonella from chickens and the prevention and treatment of infection in Hebei Province.
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维普
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