ICMSF Methods Studies. XIV. Comparative Study on Recovery of Salmonella from Refrigerated Preenrichment and Enrichment Broth Cultures

Abstract

Twelve laboratories from 7 countries compared the productivity of refrigerated (72 h at 5 to 10°C) preenrichment and enrichment broth cultures with a standard cultural procedure for detection of Salmonella in 466 naturally contaminated low and high moisture foods. Refrigerated preenrichment and enrichment cultures identified 92.5 and 94.2% of contaminated samples, respectively. Variations in the ability of laboratories to successfully recover salmonellae under refrigeration test conditions were notable. Three laboratories found complete agreement between results by the standard and refrigeration test procedures and 5 additional laboratories reported >90% accuracy; lowest recovery rate for combined refrigeration results was 77%. Sensitivity of the refrigeration techniques was markedly greater with low than high moisture foods where the latter contributed all but two of the 62 false-negative results encountered in this study. Ability of individual laboratories to recover Salmonella from refrigerated preenrichment and enrichment broth cultures was not significantly different for given food categories. Productivity of paired enrichment-plating media differed widely with food type. Selective enrichment in tetrathionate brilliant green and plating on bismuth sulfite agar showed greatest sensitivity for isolation of Salmonella in high but not in low moisture foods where productivity of the 4 enrichment-plating conditions used in this study was comparable. Results on recoverability of Salmonella from refrigerated broth cultures concur with findings of an earlier comparative study and strongly support incorporation of this novel approach in standard cultural methods for detection of Salmonella in foods.

Detection of Salmonella by the Enzyme Immunoassay (EIA) Technique

“…cell concentration. The poor performance of S& was not unexpected because the low selectivity of this medium cannot effectively cope with the large populations of nonsalmonellae obtained from cultured raw meats and low moisture foods such as animal feeds (D'Aoust, 1984;D'Aoust et al, 1983). Performance of the TBGMd3 medium which had been formulated in the hope of successfully combining selective enrichment in TBG and post-enrichment in M broth into a single analytical step was unremarkable.…”