Detection of group D Salmonellae including Salmonella enteritidis in eggs by polymyxin-based enzyme-linked immunosorbent assay

A high-throughput, rapid method was devised for the detection of Salmonella Enteritidis in egg products. For each target organism, preenrichment in nutrient broth was followed by selective enrichment in Rappaport-Vassiliadis soya peptone and tetrathionate brilliant green broths or by plating on modified semisolid Rappaport Vassiliadis (MSRV) agar medium. The presence of Salmonella Enteritidis was determined by subjecting portions of the selective broth cultures or swarming growth on MSRV medium to an enzyme-linked immunosorbent assay (ELISA) procedure using polymyxin immobilized in the wells of a microtiter plate as a high-affinity adsorbent for lipopolysaccharide (LPS) antigens. Sample extracts were reacted with polymyxin-coated microwells, and captured LPS antigens were detected immunoenzymatically with a commercially available Salmonella factor O9-specific antibody. The polymyxin-ELISA was 100% sensitive and 100% specific for Salmonella strains bearing the O9 antigen. When the ELISA was combined with enrichment using either the selective broths or plating on MSRV medium, the system was an effective means for detection of Salmonella Enteritidis in artificially inoculated egg products. The polymyxin-ELISA is a simple and inexpensive assay for group D salmonellae (including Salmonella Enteritidis) in a convenient 96-well microtiter plate format, making this system ideally suited for processing large numbers of samples.