Problems with Radiometric Coliform Assays

A study has been made of the feasibility of adapting conventional media for coliform assays to rapid radiometric techniques. A variety of media included Lauryl Tryptose, British MacConkey, m-Endo-MF, Nutrient and Brilliant Green Bile broths. Radioactive substrates included 1-C14 Lactose, 1 and 6C14 glucose and C14 formate. One ml samples of 24-hour cultures diluted in phosphate buffered water were inoculated into 9 ml of radiometric medium in vaccine capped vials. They were incubated at 35C on a rotary shaker at 200 rpm. The time to detect a significant level of C(14)O2 varied inversely with the logarithm of the inoculum of several coliform species. A lack of specificity of the techniques was revealed when several strains of Escherichia coli were studied individually in addition to strains of Enterobacter agglomerans, Pseudomonas aeruginosa, Proteus inconstans, Proteus morganii and Salmonella St. Paul. Non-coliform species produced C(14)O2 in the radiometric media tested. (Author)