Comparison between semisolid Rappaport and modified semisolid Rappaport-Vassiliadis media for the isolation of Salmonella spp. from foods and feeds

Abstract

Two semisolid media poured in petri dishes, semisolid Rappaport and modified semisolid Rappaport Vassiliadis were compared for the recovery of Salmonella spp. from 154 high- and low-moisture foods and feeds. Semisolid media were inoculated after pre-enrichment in buffered peptone water and after enrichment in Müller-Kauffmann tetrathionate broth and selenite cystine broth. Also a conventional procedure was used, where the enrichment broths were streaked on Brilliant Green and bismuth sulphite agars. Of 62 samples found positive for Salmonella by one or more methods, semisolid Rappaport detected all of them and 60 when inoculated directly from the pre-enrichment broth. Modified semisolid Rappaport-Vassiliadis gave only 20 positive samples. The difference in productivity between semisolid Rappaport and the other media poured in plates (modified semisolid Rappaport-Vassiliadis, Brilliant Green and bismuth sulphite agar) was statistically significant (P less than 0.001). The incubation temperature recommended for modified semisolid Rappaport-Vassiliadis (42 degrees C) was found to be too high. By comparison to the other media, semisolid Rappaport gave a 500% increase in the detection of the enteritidis serotype of Salmonella.