Simplified preparation of a specific S. enteritidis antigen for ELISA and other immunological techniques

Cultural and Immunological Detection Methods for Salmonella spp. in Animal Feeds - A Review

Food-borne salmonellosis continues to be a major public health concern, and contamination with Salmonella spp. in pre-harvest animal production is considered a primary contributor to this problem. Animal feeds can easily become contaminated during primary production, feed mixing and processing as well as during feeding. Consequently, monitoring and surveillance of feeds and feed ingredients for Salmonella spp. contamination may be useful or necessary in the prevention and control of this organism. Cultural and immunological detection methods for salmonellae have been used or suggested as possible approaches for use in animal feeds. Cultural methods remain advantageous owing to their ability to detect viable bacterial cells, while immunological methods have the capability of detecting nonculturable bacterial cells. Advancements and improvements in both methodologies offer opportunities for eventual routine use of these detection technologies in animal feed assays.

Antigen-specific lymphocyte proliferation and interleukin production in chickens immunized with killed Salmonella enteritidis vaccine or experimental subunit vaccines

Lymphocyte proliferation and interleukin (IL)-2 and IL-6 levels in serum were measured as indicators of cell-mediated immunity after immunization of chickens with a commercial killed Salmonella enteritidis (SE) vaccine or experimental subunit vaccines of crude protein (CP) extract or the outer membrane protein (OMP). Significantly increased proliferative responses to SE flagella, but not lipopolysaccharide, porin, CP, or OMP, were observed at 1 wk postimmunizarion in the three vaccination groups. The responses to flagella were specific because flagella-induced proliferation was not seen in chickens immunized with adjuvant alone. Of the three immunization protocols, use of the killed SE vaccine appeared most effective because it induced higher flagella-stimulated lymphocyte proliferation at 1 and 2 wk postvaccination compared with the CP- and OMP-vaccinated groups. Significantly increased IL-2 and IL-6 levels in serum were seen at 1 wk postimmunization in the three vaccination groups compared with adjuvant alone, but there were no differences between the killed vaccine and the subunit vaccines at this time, and the levels of both lymphokines returned to baseline at 2 wk postimmunization. We conclude that cell-mediated immunity to SE after vaccination with the killed bacterial vaccine or subunit vaccines is transient and mainly limited to flagella.

Sensitive and rapid immunoassays for Salmonella enteritidis

In order to develop more sensitive, specific, and rapid immunoassays to detect Salmonella enteritidis in food supplies, we have applied various approaches by using several different antibody preparations. Utilizing ELISA in both a plate and immunodot assay, we employed (i) a polycolonal rabbit antiserum to a boiled suspension of the organism; (ii) a monoclonal antibody to the cell surface of the bacterium; and (iii) mouse antisera to two oligosaccharides each containing the rare sugar tyvelose, and exhibited by S. enteritidis, a member of the group D salmonellae. We showed that the polyclonal antiserum and monoclonal antibody IG-10 to the cell surface could specifically detect from 10(2) to 10(3) organisms in a 10-microl sample in the plate and immunodot assay. Both assays are read in 4-5 hr. Further, in the mice immunized to the trisaccharide, (alpha-D-galactose-alpha-tyvelose-alpha-D-mannose), as well as those mice immunized to the tetrasaccharide, (alpha-D-galactose-alpha-tyvelose-alpha-D-mannose-alpha-L-rhamnose), specificity to tyvelose was determined by inhibition studies. The inhibitors of the antisera to the trisaccharide included the single sugar tyvelose conjugated to bovine serum albumin (BSA), a tetrasaccharide in which tyvelose is excluded, but contains alpha-D-galactose, alpha-ascarose, alpha-D-mannose, and alpha-L-rhamnose (conjugated to BSA), and others. The inhibition studies suggest that the mouse antisera are specific for tyvelose and also contain antibodies for mannose and rhamnose. The antibodies that have been made to the unique sugar tyvelose should improve the specificity in assays for S. enteritidis.