Answer:
The food that is contaminated with spoilage bacteria are quite dangerous for human health. These foods are drastically infected even if they don't look that bad. These bacteria get access to the food items and utilize the valuable nutrients that are present in it and they multiply and form more in number. The color of the food gradually changes, the taste also changes into a somewhat sour type and produces a foul smell.
Thus, these are some of the indications that the food is not safe to eat as they are contaminated with spoilage bacteria.