Predictive models for the occurrence of viable but non-culturable (VBNC) bacteria under various environmental stresses

The survival of Enterococcus faecalis under different environmental stresses (salinity, starvation and sunlight) were examined under controlled conditions in the laboratory. Different decay kinetics were observed for measurements of the bacteria using a culture-based method and a molecular technique (PMA-qPCR). The cell counts for the culture-based method were found to be generally lower than PMA-qPCR over time in the stressed microcosms. This phenomenon suggests the entry of the cells into another physiological state i.e. the viable but non-culturable (VBNC) state. The difference between the two enumeration methods (i.e. the VBNC cells) was modelled as a function of environmental variables. The decay coefficients (k values) showed a strong correlation with light irradiation. In addition, this study demonstrated the ability of E.faecalis to adapt to a wide range of salinity. Models were developed to predict the occurrence of VBNC cells under stressed conditions from light irradiation. These models can enhance current water quality models by providing a more accurate picture of the microbial community's survival characteristics.