Real-time fluorescence growth curves for viable bacteria quantification in foods

Here, for the first time, we used a membrane permeable fluorescent nucleic acid stain (SYBR Green) to trace the in-vivo DNA replication during bacterial binary fission. Such stain did not influence the growth of bacteria. Nor did the bacteria degrade the stain, enabling the fluorescent microplate reader to monitor sensitively the growth of the bacteria. Hence, a real-time fluorescence growth curve (RTFGC) method was put forward for the sensitive quantification of viable bacteria in foods. Using <i>E. coli</i> O157:H7 as a bacteria model, the RTFGC method could quantify bacteria within the range of 10 to 1 × 10⁶ cfu/mL, with a linear correlation coefficient R² of 0.997. It was found that melting curve was unique for a particular bacterial strain, which could be used for contamination identifications. Good practicability of the RTFGC in quantifying <i>E. coli</i> O157:H7 from tap water, juices, and milks was demonstrated.