EFFICACY OF PROLONGED (48-H) SELECTIVE ENRICHMENT FOR THE DETECTION OF FOODBORNE SALMONELLA

The effect of prolonged (48 h) incubation on the productivity of five enrichment-temperature conditions (tetrathionate brilliant green, 35 and 43-degrees-C; Muller-Kauffman tetrathionate brilliant green, 43-degrees-C; Rappaport-Vassiliadis, 43-degrees-C; selenite cystine, 35-degrees-C) was compared to homologous results obtained under standard (24 h) conditions of selective enrichment. Of 797 high moisture and 166 low moisture foods tested, 171 (21.5%) and 80 (48.2%), respectively, were found to contain salmonellae by one or more analytical condition. Combined results of the five enrichment conditions after 24 and 48 h of incubation identified 247 (98.4%) and 250 (99.6%) of the 251 contaminated samples identified in this study. Our results are at variance with earlier reports on the greater method sensitivity with extended (greater-than-or-equal-to 48 h) periods of selective enrichment. The productivities of individual enrichment conditions after each period of incubation varied markedly where recovery rates with TBG43 and MKTBG43 exceeded that obtained with SC35 and TBG35. Our findings also underline the determination role of enrichment at an elevated temperature (43-degrees-C), and use of multiple enrichment and plating media for the optimal recovery of foodborne Salmonella.