RAPID AND ECONOMICAL DETECTION OF SALMONELLA-ENTERITIDIS IN EGGS BY THE POLYMYXIN-CLOTH ENZYME-IMMUNOASSAY

A rapid, simple and economical procedure for the detection of Salmonella enteritidis in eggs was developed. The contents of whole eggs inoculated with low numbers of S. enteritidis were mixed with a minimal volume of a nutrient-rich broth (1:2 ratio of egg to broth) and incubated overnight. The lipopolysaccharide (LPS) antigens of S. enteritidis were extracted by heating in the presence of cholate. The antigens were captured on polymyxin-coated polyester cloth, and the captured antigens were detected by sequential reactions with anti-serogroup D1 rabbit antiserum, anti-rabbit antibody-peroxidase conjugate and tetramethylbenzidine substrate solution. This polymyxin-cloth enzyme immunoassay (polymyxin-CEIA) was highly specific for salmonellae bearing the factor 0:9 antigen, reacting in the assay of 19 S. enteritidis strains tested, including two rough isolates, but not with salmonellae lacking the factor 0:9 antigen or non-Salmonella bacteria. The threshold sensitivity of the polymyxin-CEIA for S. enteritidis suspensions was ca. 10(6) cfu/ml. This combined enrichment culture and polymyxin-CEIA required less than 24 h to complete and detected as few as 1-2 S. enteritidis cfu inoculated into a whole egg. This procedure should facilitate the routine monitoring of S. enteritidis in large numbers of egg samples.