Many differential media have been devised for the identification of Shigellae, Salmonellae, and other enteric pathogens. None of them, however, had been designed for the determination of the activity of lysine decarboxylase, indole production, and motility of these organisms in a single tube of medium.
The present investigation was undertaken with an objective to reduce the man-hour and to simplify the conventional tedious procedures when a large number of samples were involved. The medium developed in it met those criteria and was named lysine-indole-motility (LIM) medium.
1) Composition and usage: LIM medium was composed of 10.0g of polypeptone (Daigo Eiyo Chemicals Co.), 3.0g of yeast extract (Difco), 1.0g of glucose, 10.0g of L-lysine monohydrochloride, 0.5g of L-tryptophan, 0.02g of bromcresol purple, 3.0g of agar, and 1, 000ml of distilled water. After these components were dissolved by heating at 100°C, pH was adjusted to 6.7±0.1. The resulting medium was dispensed into 10×100mm tubes in 3∼4ml amounts and sterilized at 121°C for 15 minutes. After the sterilization, the medium was cooled immediately by putting it into cold water. At use, organisms were picked up from a suspicious colony and stabbed into the middle of the medium. After 24 hours incubation at 37°C, reading was made.
2) Results of comparative study: Comparison of results was made between LIM medium and some known differential media. A total of 120 Salmonella strains, 166 Shigella strains, and 87 strains of the other enteric pathogen were used. There was a complete agreement on results. Therefore, the sensitivity and accuracy of the medium were demonstrated. Furthermore, in routine diagnostic use, all the enteric pathogens could be tested easily with the new medium in combination with triple sugar iron (TSI) agar.