Establishment of indirect ELISA method for Salmonella antibody detection from ducks based on PagN protein.

BACKGROUND: Salmonella as an important food-borne zoonotic bacterial pathogen, infection in ducks is a recessive infection, however, it can also cause high mortality and threat to food safety. Preventing and controlling the infection and transmission of Salmonella in ducks critically require rapid and sensitive detection method. Full-length Salmonella-specific protein PagN was induced and expressed in E.coil BL21 and was purified as an antigen to establish an indirect enzyme-linked immunosorbent assays (iELSA) detection kit. RESULTS: The recombinant PagN protein has a molecular weight of 43 kDa containing a His-tag, was recognized by an anti-Salmonella positive serum by Western blot assay. The optimal concentration of PagN as a coating antigen in the iELISA was 1 µg/mL, and the optimal dilution of enzyme-labeled secondary antibody was 1:4000 (0.025 µg/mL). The cutoff OD450 value was established at 0.268. The iELISA kit showed high selectivity since no cross-reaction with E. coli, Staphylococcus aureus and Streptococcus was observed. iELISA method and Dot-blot test were performed on 100 clinical sera samples collected from duck farms, and the actual coincidence rate was 89% (89/100). 613 duck serum samples from 3 different farms were tested using established method and commercial ELISA kit. The concordance between the two methods was 94.1%. CONCLUSION: Anti-PagN based iELISA can serve as a useful tool for diagnosis of Salmonella infection.

Epidemiological investigation on drug resistance of Salmonella isolates from duck breeding farms in Shandong Province and surrounding areas, China.

Duck salmonellosis is a common acute septic infectious disease that spreads rapidly, with serious harm to the duck breeding industry and public health. To date, there are few reports about the epidemiological characteristics of drug resistance in Salmonella from ducks. In this study, an epidemiological investigation was conducted on drug resistance of 110 Salmonella strains isolated from multiple duck farms in Shandong Province and surrounding areas, China. The multidrug-resistant (MDR) rate for 110 Salmonella strains was up to 71.82% (79/110), and 12 types of drug resistance genes were detected in all isolates, including ß-lactams, aminoglycosides, tetracycline, macrolides, and quinolones resistance genes. Using the multilocus sequence typing (MLST) based on 7 housekeeping genes, 13 various ST types were identified among all strains, and ST19 (32/110, 29.09%) was the primary type. As the dominant serotypes, S. Kottbus and S. Typhimurium were divided into multiple ST types. A total of 6 kinds of plasmid incompatibility groups were carried in the Salmonella strains, of which IncFIIs (29/110, 26.36%) was most prevalent, and the class I integrons were detected in 78.18% (86/110) of strains. Furthermore, we found that some drug resistance genes, plasmid incompatibility groups, and class I integrons coexist in the same strain. This phenomenon indicates that class I integrons and plasmids are important ways for the spread of drug resistance genes. Therefore, the spread of antibiotic resistance in Salmonella had been facilitated, especially erythromycin (108/110, 98.18%), streptomycin (93/110, 84.54%), and tetracycline (53/110, 48.18%). The above research results broadened ideas and provided directions for the transmission mechanism of Salmonella resistance.