| Duck salmonellosis,also known as duck paratyphoid,spreads quickly,and the mortality rate of young ducks is high.Adult ducks often pass recessively and become one of the main sources of transmission.In recent years,salmonellosis has become an important bacterial disease,causing serious economic losses to the duck industry.In the process of preventing and treating the disease,due to the abuse of antibiotics,the resistance of Salmonella was increased,and even appeared multi-drug resistance.In this study,we first used selective media,PCR,and biochemical identification methods to isolate and identify Salmonella from220 fecal samples collected from duck farms in Henan and Zhejiang province,and then conducted serotyping and antimicrobial resistance testing.Afterward,the strain with higher prevalence was selected to perform pathogenicity assays and genome sequencing,subsequently,predict the resistance genes and prophage sequences which they carried for exploring the possible drug resistance mechanism and clinical prevention strategy of Salmonella.The results showed that 18 strains of Salmonella from duck were isolated.The serotype test found that these strains belonged to 4 serotypes,including 14 strains of Salmonella indiana,1 strain of Salmonella Tumodi,1 strain of Salmonella Argonne,and 2 strains of Salmonella Alton.The antimicrobial resistance testing showed that these duck-originated Salmonella isolates were highly sensitive to doxycycline and suitable for clinical treatment.Whereas,the resistance rate to cefoperazone,tetracycline,norfloxacin,pipemidic acid,and trimethoprim is relatively high,reaching 75%,and 15 of them even possessed multi-drug resistance.The results of the animal pathogenicity test showed that the half lethal dose of Salmonella Indiana 47 isolate was 1.553×10~8.After ducklings were infected with Salmonella from ducks,they showed obvious symptoms of Salmonella infection.The liver,heart,and spleen all had certain pathological changes.Liver damage is more typical,from which the pathogenic strain SAP is obtained.According to the genome sequencing result of the SAP isolate,10 resistance genes were annotated from the NR datebase,10 resistance gene clusters were predicted against the CARD datebase,and five prophage-related insertion sequences were obtained.These resistance genes were fluoroquinolones resistance gene gyr B,fosfomycin resistance genes glp T,Uhp A and Uhp T,cephalosporin resistance gene bla SPG-1,peptide antibiotic resistance gene van RI,and mediating macrolides and cephalosporins MFS efflux pump family genes Aba F and Aba Q,RND efflux pump family genes ade L and CRP,which are resistant to antibiotics,tetracyclines,aminoglycosides,quinolones,diaminopyrimidines,etc.The five prophage-related insert sequences are highly similar to Salmonella phage epsilon 34 and Salmonella phage SJ46.The gtr ABC gene cluster of epsilon34 is related to the host serotype.The bla CTX-M-27 resistance gene carried by SJ46 phage can be vertical and horizontal spread.In summary,18 strains of duck-originated Salmonella were isolated and identified from duck farms in Zhejiang and Henan province,which belonging to 4 serotypes,showing resistance to a variety of antibiotics.Furthermore,there is a certain correlation between these resistance phenotype and their resistance genes and gene clusters.This study will lay a theoretical foundation for further exploring the pathogenic and drug resistance mechanisms of pathogenic Salmonella,and are also expected to provide a theoretical basis for the prevention and control of Salmonella in these areas. |
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