The efficacy of enzyme immunoassays for the detection of salmonellas

Abstract

Two commercially available enzyme immunosorbent assay kits for the detection of Salmonella (‘ Salmonella Bio-EnzaBead Screen Kit’ and ‘ELISA Screening Kit for Salmonella’) were tested and compared with the standard isolation procedure. For this purpose, buffered peptone water was inoculated with Salmonella reference samples (10), with minced meat (10) or with a combination of Salmonella reference samples and minced meat (25). The minced meat appeared to be naturally contaminated with salmonellas; for this reason interpretation of results was complicated. With the ‘Bio-EnzaBead Screen Kit’ 35 enrichments were found to be positive, in comparison with 28 by the ‘ELISA Screening Kit’ and 32 by the standard isolation method. Evidence suggested that the standard isolation method and the ‘ELISA Screening Kit’ in particular gave a number of false-negative results. The growth of salmonellas in enrichment broths and therefore the Salmonella detection can be influenced by growth of competing micro-organisms. For this reason it was not possible to prove that some positive results with the ‘Bio-EnzaBead Screen Kit’ were true-positive instead of false-positive results. It is concluded that EIA tests are useful alternatives to conventional Salmonella isolation procedures from a selective enrichment broth, although they show similar susceptibility to the influence of competing flora. This latter aspect is discussed in detail.