Comparison of Rappaport-Vassiliadis Enrichment Medium and Tetrathionate Brilliant Green Broth for Isolation of Salmonellae from Meat Products

Abstract

The effectiveness of Rappaport-Vassiliadis enrichment medium (RV medium) and Difco's tetrathionate brilliant green broth (TBG) for detection of Salmonella in 553 samples of meat products was compared. All samples were preenriched for 20 h in buffered peptone water. Then 0.1 ml of the preenrichment was inoculated into 10 ml of RV medium, 1 ml was added to 9 ml of TBG broth, and 1 ml was inoculated into 10 ml of Muller-Kauffman (MK) tetrathionate broth. All enrichments were incubated at 43°C for 24 h, except for MK broth which was incubated for 48 h, and all were subcultured onto brilliant green deoxycholate agar and bismuth sulfite agar. The Rappaport-Vassiliadis medium was superior to Difco's tetrathionate brilliant green broth, being considerably more sensitive and more specific. The superiority of RV medium concerned the number of positive samples (36% and 28%, respectively), and also the number of Salmonella serotypes and strains. The RV medium inhibited the lactose- and sucrose-negative competing organisms much more than the Difco's tetrathionate broth. The performance of Difco and Muller-Kauffman tetrathionate brilliant green broths was similar. Addition of the brilliant green solution after boiling the tetrathionate broth slightly increased its efficacy. The effectiveness of brilliant green deoxycholate agar and bismuth sulfite agar was similar, whether after enrichment in RV medium or in any of the studied tetrathionate brilliant green broths.