Rapid and economical detection of Salmonella enteritidis in eggs by the polymyxin-cloth enzyme immunoassay

Abstract

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 polymyxincoated 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.