Rapid and convenient estimation of bacterial cell count in food using oxygen electrode sensor

Bacterial respiration measurement method with oxygen electrode sensor has been applied to estimate the bacterial cell count in foods. The relationship between respiration of bacteria and its bacterial cell count was examined with the newly developed O2 uptake detector and the conventional agar-plate. Using 168 food samples, the new method was evaluated. Samples were processed with a stomacher for one minute in saline, and injected into the ninety-six well sensor plate with oxygen electrodes embedded. After nutrient broth was added to each well, dissolved oxygen concentration of each sample was monitored continuously for 24 hours at a temperature of 35°C. Detection time for oxygen electrode method was defined as the elapsed time when the dissolved oxygen is consumed by bacterial respiration to 60% of negative control oxygen concentration. It depended on the number of conventional plate count. As for samples containing 105 [cfu/g] bacteria, detection time was approximately 6 hours, and it decreased linearly with the log number of standard plate count, with a slope of -2.6 [hour/cfu/g]. Correlation coefficient for the estimated cell count with reference curve and conventional plate count was 0.83. This new method detected bacteria more rapidly, in proportion to bacterial concentration in foods.