Evaluation of methods for isolation of Salmonella species using modified semisolid Rappaport-Vassiliadis medium and Salmonella-Shigella agar.

A total of 197 Salmonella strains were isolated from 1717 stool samples on salmonella-shigella agar and modified semisolid Rappaport-Vassiliadis medium before and after enrichment in selenite broth. Better sensitivity was obtained with salmonella-shigella agar than in direct plating (89.2% vs. 64.4%, P<0.0001) and after broth enrichment (96.4% vs. 88.1%, P<0.01). The incidence of false-positive results using modified semisolid Rappaport-Vassiliadis medium was higher than that obtained using salmonella-shigella agar combined with the oxidase and C8 esterase tests in direct plating (33 vs. 2 strains) and after enrichment (43 vs. 0 strains). Thus, based on its performance modified semisolid Rappaport-Vassiliadis medium could be a suitable option for isolation of salmonellae from stool samples in clinical microbiology laboratories.