RAPID DETECTION AND COUNTING OF VIABLE BACTERIA IN VEGETABLES AND ENVIRONMENTAL WATER USING A PHOTON-COUNTING TV CAMERA

A bioluminescence assay carried out with a photon-counting TV camera w as evaluated for rapid enumeration of viable bacterial counts. The tes t sample was filtered through a membrane filter, and the membrane filt er retaining bacteria was incubated at 37 degrees C for 6 h on a filte r paper soaked with nutrient broth supplemented with 0.5% NaCl. The me mbrane filter was then subjected to a bioluminescence reaction, and th e intensity of light and numbers of light emission points on the filte r were measured with a photon-counting TV camera. The light intensity measured on seven different bacteria correlated with initial viable co unts; the correlation coefficient was calculated to be 0.89. The numbe r of light emission points measured on Escherichia coli also correlate d with the initial viable counts (r = 0.81) in a range from 1 to 100 C FU. Presumptive bacterial counts by the present bioluminescence assay determined on 79 samples of vegetables and 122 samples of environmenta l water correlated well with the viable counts obtained by the convent ional plating method, with correlation coefficients of 0.87 and 0.82, respectively.