Extraction of Salmonella antigens in non-sedimentable forms for enzyme immunoassay

Heating Salmonella typhimurium in ethylenediaminetetraacetate was found to dissociate its antigens into forms that are non-sedimentable at 10,000 x g. The treatment caused a marked increase in the rate of immunoreaction and the sensitivity in an enzyme immunoassay for the detection of Salmonella antigens. The method permits the extraction of Salmonella antigens from solid-rich samples and the preparation of solid-free samples by means of centrifugation. When the level of the antigens in the supernatant was too low for the immunoassay, the antigens were readily concentrated by passing a large volume of the supernatant through a macroporous hydrophobic cloth coated with anti-Salmonella antibody. Using this method, the detection of as few as 10 Salmonella cells per gram of chicken meat was possible within a total of 18 h, which included 16 h of enrichment in either tetrathionate, selenite cystine, or nutrient broths.