A MEDIUM FOR ISOLATION OF THE COLON GROUP

Abstract

The use of bile, or bile salts in media for the isolation of the colon group of organisms, has now been practised for about twelve years, and its place in the fixed laboratory procedure has been generally established and acknowledged by all workers along these lines. The use of bile salt (sodium taurocholate) was first proposed by McConkey in 1900. This was followed by Jackson, who in 1906 advocated the use of fresh sterile ox bile to which peptone and lactose had been added. *Since that time many modifications of these two substances have been proposed, but all are built upon the use of either the bile or bile salt as the basis. Recently the dried ox bile has been placed upon the market, and so far as the writer is aware, has given satisfactory results. The writer has used both the fresh and dried product in the work in his laboratory, and finding no appreciable difference in their action toward the colon group, has discontinued the use of the fresh bile. The dried product is more easily obtained, is more convenient to use, and has been found no more expensive, taking all points into consideration. Some experimental work was undertaken this past year to find a more satisfactory medium than litmus lactose agar for the isolation of the colon group from water. The work was interrupted at times, so the studies have not been carried as far as intended, but it is expected that additional work will be done along the lines suggested in this brief report. As is well known, not all red colonies on litmus lactose agar prove to be of the colon type, and a medium giving a larger number of positive tests is desirable. A medium of the following composition was devised and tested for adaptability to this line of work: