A promising detection candidate for flagellated Salmonella spp.

Salmonella is a common and important pathogen for both human and animals. All Salmonella except Salmonella pullorum and Salmonella gallinarum have flagellum. Flagellin (FliC) is the main subunit protein forming the bacterial filament, which is present in large amounts on the surface of all flagellated Salmonella. After bioinformatics analysis, the most highly conserved region (locates position from 1 to 102 amino acid residue of FliC, we named it as FliC′) was selected, and corresponding recombinant FliC′ (rFliC′) protein was tailored as an immunogen to generate monoclonal antibodies (MAbs) against Salmonella flagellin. BALB/c mice were immunized with the purified recombinant protein rFliC′, which were prepared by prokaryotic expression system pET22b (+) expressing FliC′. After fusion of spleen cells from the immunized mice and SP2/0 cells, three hybridoma cells (1D6, 2G6 and 3E2) producing MAbs against targeted flagellate Salmonella FliC′ were generated and screened. The ability of MAb 3E2 to recognize and bind to Salmonella flagella was demonstrated by immunogold electron microscopy (IEM) method. Western blot (WB) analysis demonstrated that MAb 3E2 could specifically recognize flagellated Salmonella strains. Moreover, MAb 3E2 has a direct agglutination activity against Salmonella strains with visible agglutination reaction. To further verify this agglutination activity, a total of 52 flagellated Salmonella strains (23 serovars), 8 non-flagellate Salmonella strains (2 serovars) and 16 other non-Salmonella bacteria strains were used to evaluate the specificity of the MAb by direct Slide Agglutination Test (SAT). Results showed that MAb 3E2 reacted with all Salmonella strains possessing flagellum and had no cross-reaction with non-flagellate Salmonella strains or other non-Salmonella bacteria strains. Sequentially, the ability to detect the presence of Salmonella in raw samples of the MAb 3E2-based SAT method was evaluated. The conventional culture-based detection method was performed as the standard reference method for detection of Salmonella. Altogether, 369 samples collected from laying hens were tested, and the results indicated that the MAb 3E2-based SAT method could specifically detect Salmonella. Furthermore, the SAT results were obtained more quickly, as compared with the standard method. As a whole, the MAbs against the tailored conserved region of Salmonella flagellin were prepared in this study, and MAb 3E2-based SAT is a promising candidate for the flagellated Salmonella spp. rapid detection. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13568-019-0851-0) contains supplementary material, which is available to authorized users.