Abstract: 【Objective】 In order to prevent and control duck Salmonella infection, this test was conducted to study the infection of duck Salmonella in Deyang, Sichuan.【Method】 222 samples of different types were collected from 3 duck breeding farms and 1 duck incubator in the region, and Salmonella was isolated and identified according to GB 4789.4－2016. Further, the sensitivity of the isolated bacteria to 14 antibiotics was detected by K-B method, and the pathogenicity of the identified rare Salmonella serotype was studied.【Result】 The suspected Salmonella isolates were black, gray or brownish, metallic colonies on BS agar and colorless, transparent, or black or almost all black colonies on XLD agar.The suspected Salmonella isolates were inoculated with trisaccharide iron agar slant for biochemical identification.The suspected Salmonella isolates could make the trisaccharide iron slant turn red and the bottom turn yellow with black, which conformed to the biochemical characteristics of Salmonella.The specific gene invA of Salmonella was amplified by PCR.After agarose gel electrophoresis, the target band was observed above 500 bp.It was confirmed that 17 Salmonella strains were isolated, with a total isolation rate of 7.7% (17/222).The 17 strains of Salmonella included three serotypes, namely Salmonella Typhimurium, Salmonella Hato and Salmonella Bonn, with the proportions of 47.1% (8/17), 29.4% (5/17) and 23.5% (4/17) respectively.The predominant serotype is Salmonella Typhimurium.The isolates were the most resistant to β-lactams and aminoglycosides, and the resistant rates to ampicillin and streptomycin were 82.4% (14/17) and 88.2% (15/17), respectively.The isolates were the most sensitive to quinolones, and 100% (17/17) to nalidixic acid.The isolated bacteria had serious multi-drug resistance, six strains were resistant to more than 10 kinds of antibiotics (including 10 kinds), accounting for 35.2%.And the 10 kinds of antibiotics were from at least 6 different kinds of antibiotics.Two strains were resistant to 8 kinds of antibiotics, accounting for 11.8%.Six strains were resistant to 5-7 kinds of antibiotics, accounting for 35.3%.A total of 3 strains were resistant to 2-3 antibiotics, accounting for 17.6%.The LD₅₀ of rare serotype strains H4 and B2 were determined to be 3.98×10⁶ and 1.58×10⁶ CFU respectively by Karber’s modified method.The results of pathogenicity test showed that both Salmonella Hato and Salmonella Bonn could cause acute death, organ congestion, hemorrhage, cell degeneration and other pathological changes in mice.【Conclusion】 In this study, 17 strains of Salmonella from ducks were successfully isolated, it was the first time that Salmonella Hatto was isolated from ducks at home and abroad.The isolates had serious drug resistance and multiple drug resistance, the two rare serotypes of Salmonella had strong pathogenicity to mice, and the pathogenic effects were similar.This study could provide a reference for the prevention and treatment of salmonellosis in duck farms.

Key words: Salmonella; serotypes; drug resistance; pathogenicity