Usefulness of selenite F enrichment broth for the isolation of Salmonella from stool

Lee, Mi Ae

Abstract

BACKGROUND: Stool culture for enteric pathogens constitutes a significant portion of the workload in clinical microbiology. Several reports recommended that selenite enrichment have been used only in stool cultures from suspected carriers, during outbreaks, and other special circumstances for cost-effectiveness. We evaluated the usefulness of selenite F enrichment for the isolation of Salmonella in routine stool cultures.
METHODS
Stool specimens submitted from March to October, 1999 were inoculated onto MacConkey(Mac) agar and Salmonella-Shiegella(SS) agar and into Selenite F(SF) enrichment broth. After overnight incubation, the SF broth was subcultured onto a second SS agar.
RESULTS
Total 45 strains of Salmonella spp. were recovered from 1,338 stool specimens and Shiegella or other enteric pathogens were not recovered. Twenty out of the forty-five Salmonella spp.(44%) were recovered on Mac agar and 33 of 45 Salmonella spp.(73%) on SS agar, 45 out of 45 Salmonella spp.(100%) after SF enrichment and 35 of 45 Salmonella spp.(78%) on Mac and/or SS agar. Ten Salmonella spp. were recovered only after SF enrichment, but no Salmonella spp. were recovered only on the primary Mac agar or SS agar. After SF enrichment, Salmonella spp. grew more purely and heavily than on the primary medium.
CONCLUSIONS
These results suggest that SF enrichment is necessary to routine stool cultures and the elimination of the primary Mac or SS agar is cost-effective than the elimination of SF enrichment.