Development of a rapid test for the enumeration of Escherichia coli in foods

All strains of E.coli possessing glucuronidase activity can be detected in 13 h by fluorescene when its substrate 4 methyl umbelliferyl β-D glucuronide (MUG) is incorporated in the growth medium. Solid and liquid media containing MUG were compared for the enumeration of E.coli in pure cultures and food samples Studies revealed very good correlation(correlation coefficient -0.986) between the two methods of enumeration. Relationship between fluorescence detection time (FDT) and initial cell concentration of the inoculum was established. FDT was inversely proportional to the initial cell concentration. FDT of 1-13 h corresponds to cell concentrations of 10 9 -10 1 cells/ml. A minimum of 10 8 cells/ml were required to produce visible fluorescence. A rapid single step method was standardised by adding 1 g of the sample directly to MUG containing broth and FDT was determined. Cell concentration was obtained from the graph (cell concentration v/s FDT). This method can be employed to enumerate E.coli in culture broth as well as food samples like raw meat, pasteurised milk and fresh/raw vegetables.