Limited Sensitivity of Short (6 h) Selective Enrichment for Detection of Foodborne Salmonella

Abstract

Short (6 h) enrichment under five different selective conditions adversely affected the isolation of Salmonella from pre-enriched samples of naturally contaminated foods. Of the 109 high moisture and 18 low moisture foods found to contain salmonellae following conventional (24 h) enrichment, combined results of the abbreviated enrichment procedures identified only 99 (90.8%) and 13 (72.2%) contaminated samples, respectively. The productivities of tetrathionate brilliant green (TBG43) and Muller-Kauffman tetrathionate (MKTBG43) broths consistently exceeded that obtained with the modified Rappaport (RV43), tetrathionate brilliant green (TBG35), and selenite cystine (SC35) media after 6 and 24 h of incubation. Semi-quantitative analyses of growth under all enrichment conditions indicated that short (6 h) enrichment negatively affected method sensitivity through reduced numbers of Salmonella colonies and heavy growth of nonsalmonellae on bismuth sulfite (BSA) and brilliant green sulfa (BGS) plating media. These findings raise concerns on the dependability of commercial diagnostic schemes that incorporate abbreviated (6 h) enrichment in TBG35 and/or SC35 in their analytical protocol.