Isolation of salmonellae using two forms of Rappaport-Vassiliadis medium and brilliant green agar

The relative efficiencies of Rappaport-Vassiliadis medium containing tryptone (RV medium) or soya peptone (RV-soya) were compared for the isolation of salmonellae from 518 naturally contaminated chicken livers. RV-soya (299 of 518) gave slightly better recoveries than the standard RV medium (295 of 518) although the difference was not statistically significant (P> 0.05). 60% of the samples which were found to be positive after 24 h enrichment in RV-soya were also positive after just 6 h incubation. It was shown that the use of 14 cm plates of brilliant green agar gave better Salmonella recoveries than did 9 cm plates of the same medium. However, when sulphamandelate supplement was incorporated into the medium, recoveries were further increased. We conclude that RV-soya is an effective alternative to the standard RV medium for the isolation of salmonellae from poultry and would recommend a protocol of pre-enrichment in buffered peptone water, enrichment in RV-soya for 24 h at 43°C and plating on brilliant green agar containing sulphamandelate supplement.