Inadequacy of Small Transfer Volume and Short (6 h) Selective Enrichment for the Detection of Foodborne Salmonella

Abstract

The propensity of short (6 h) selective enrichment combined with a preenrichment to enrichment transfer volume ratio of 1:100 to provide greater method brevity could not be demonstrated. Inoculation of tetrathionate brilliant green (35 and 43°C), Rappaport-Vassiliadis (43°C), and selenite cystine (35°C) enrichment broths (9.0 ml) with 0.1 ml of preenrichment culture and incubation for 6 h identified, respectively, 107 (84.9%), 104 (82.5%), 112 (88.9%), and 113 (89.7%) of the 126 contaminated samples detected in the present study; homologous results with the 1.0-ml transfer volume showed a marginal increase in sensitivity. Recoveries of foodborne salmonellae with the standard (24-h) period of selective enrichment were generally transfer volume-independent and consistently exceeded that obtained with 6-h enrichment cultures. Results further underlined the importance of enrichment at an elevated (43°C) temperature for the effective repression of competitive microflora, and the facilitated isolation of Salmonella on plating media.