Multitest system for biochemical identification of Salmonella, Escherichia coli, and other Enterobacteriaceae isolated from foods: collaborative study

Nine laboratories evaluated the ability of the MICRO-ID test system to correctly identify members of the Enterobacteriaceae. A total of 78 isolates representing 11 genera of enterics that had been previously isolated from foods were used in the collaborative study. The collaborators streaked each isolate on plate count agar and incubated the plates overnight at 35 degrees C to check purity of the isolates. Then they proceeded with the method in which an isolated colony is transferred to a plate count agar slant and is incubated 18-24 h at 35 degrees C. Growth from the slant is emulsified in 3.5 mL physiological saline to a density comparable to a McFarland No. 2 tube and is then used to inoculate the test (MICRO-ID) strip. The strip is incubated 4 h at 35 degrees C and the reactions are read and recorded. Isolates are identified by using an octal code and the test kit manual. The system correctly identified 98.8% of the Salmonella isolates, 97.7% of the E. coli isolates, and 84.6% of the other 9 enteric genera tested. The system has been approved interim official first action as an alternative to conventional biochemical tests (1) for presumptive generic identification of food-borne Salmonella and for screening and elimination of non-Salmonella isolates; (2) for identification of E. coli from foods; and (3) for presumptive generic identification of other Enterobacteriaceae isolated from foods.