**9. The viable but nonculturable (VBNC) state**

*E*. *coli* viability has been reported to decrease when the cells are exposed to direct sunlight because they enter a viable but nonculturable (VBNC) state, while retaining pathogenic ability [45]. Some factors that are directly or indirectly linked to sample collection, storage, or processing may contribute toward *E*. *coli* entering VBNC state. These include nutrient starvation, elevated or lowered osmotic concentration, oxygen concentration, exposure to heavy metals or food preservatives, direct sunlight, and incubation outside normal temperature range [46]. These factors may lead to false-negative outcomes because *E*. *coli* does not grow on standard laboratory media when they are under VBNC state. When some of VBNC inducing factors are difficult to avoid, then *E*. *coli* detection methods that do not rely on viable or live cells, for example, DNA-dependent methods such as PCR, can be a perfect option.
