Isolation of Salmonellae from food samples. III. Dulcitol lactose iron agar, a new differential tube medium for confirmation of microorganisms of the genus Salmonella.

The many differential media designed for the clinical microbiologist have reflected his interest in the delineation of a wide variety of genera within the enteric group of organisms. The traditional differential tube media, Russell double sugar agar, Krumweide triple sugar agar, Kligler iron agar, and triple sugar iron agar (Hajna, 1945), have been invaluable aids in the prompt establishment of the biochemical patterns which are of generic significance in the identification of Enterobacteriaceae. These media were created especially for versatility in order to secure the widest applicability. In the laboratory of the food analyst, the greater emphasis placed specifically on the detection and enumeration of members of the genus Salmonella imposes a requirement for a medium designed to facilitate that technique. In previous papers, the limitations of the enrichment broths (Silliker and Taylor, 1958) and the capabilities of differential plating media (Taylor et al., 1958) have been demonstrated and discussed. The need for a simplified test for confirmation of presumptively positive colonies of Salmonella on brillant green agar plates became increasingly apparent as these works progressed. The tubed differential media used were of limited value because of the multiplicity of enteric organisms capable of producing reactions identical to the salmonellae. This, in turn, necessitated the use of many additional biochemical tests, such as several carbohydrate fermentations, indole and urease tests. An investigation to reduce the time and labor involved in biochemical confirmation of suspect salmonellae culminated in the differential medium herein described.