Evaluation of a multitest system for rapid identification of Salmonella and Shigella

The ability of Micro-ID, a multitest system for rapid (four hour) identification of Enterobacteriaceae, to identify Salmonella and Shigella was evaluated. Micro-ID, API 20E and a battery of tubed media consisting of triple sugar-iron agar, Christensen's urea agar, and Moeller's lysine decarboxylase medium were used to study 516 lactose nonfermenting strains of Enterobacteriaceae isolated from 500 consecutive pediatric stool specimens. Fifty-six of the isolates were Salmonella, and 21 were Shigella. Micro-ID correctly identified all isolates of Shigella and all but one isolate of Salmonella, whereas the conventional screening media failed to detect seven isolates of Salmonella and two isolates of Shigella. The false-positive rates were 1% and 20% for Micro-ID and the conventional battery, respectively. Use of Micro-ID as a substitute for conventional screening media for lactose nonfermenting stool isolates provides reliable presumptive idenfication of Salmonella and Shigella within four hours.