Studies on Media for Coliform Organisms

T INHERE has been considerable doubt in the minds of the writers JL as to the value of standard lactose broth as an enrichment medium for culturing coliform organisms from water and other sources when the organisms have been attenuated or when they appeared in minimal numbers. The fact that coliform organisms frequently appear in fermentation tubes after incubation periods longer than 48 hours or in tubes incubated at temperatures below 37°C. would seem to indicate that the prolonged lag phase of growth might be caused by an unfavorable environment in the nutrient medium. Little effort has been made to check the efficiency of this medium by the development of better enrichment media for comparative tests. More frequently this medium has been used as a standard to measure the value of new selective media in an attempt to produce a new medium with selected properties for the coliform organism with enrichment value equal to that of the present standard lactose broth. The appearance on the market of new peptones which are being used extensively in the growth of such pathogenic bacteria as the diphtheria bacillus and gonococcus offers an opportunity for the application of these nutrients to the growth of other organisms such as the coliform group. In this laboratory Bacto-tryptose, a peptone, which is being used extensively for the cultivation of organisms that grow scantily on Bacto-peptone media, seems particularly adaptable to this application. In most studies on the elaboration of a nutrient medium it has been customary to measure the response of the organisms to the medium by using a loopful of organisms to each tube of material