What is the best enrichment medium for suspected Salmonella infected stool specimens?

Selenite broth is considered the best enrichment medium for suspected Salmonella infected stool specimens due to its specific formulation that promotes the growth of Salmonella while inhibiting the growth of competing flora that may be present in the stool. The medium contains sodium selenite, which creates a selective environment that favors the recovery of Salmonella species. This is particularly important in stool samples, where there are often a mixed population of bacteria.

In contrast, the other mediums listed provide different environments. Blood agar is a general-purpose medium that allows for the growth of a wide variety of bacteria but does not have the selective properties needed specifically for Salmonella. Nutrient agar is also non-selective and is used for growing a variety of organisms overall, making it less effective for isolating Salmonella from a stool sample. MacConkey agar, while selective for Gram-negative bacteria and differentiating between lactose fermenters and non-fermenters, is not specifically designed for the isolation of Salmonella. Therefore, using Selenite broth allows for the enrichment of Salmonella, increasing the likelihood of detection in stool specimens.