Why are some bacteria referred to as indicator microorganisms in ascertaining microbial quality control of products?

Some bacteria are used as indicators because if they are present in the product, we can say that it is a product with the presence of pathogens that will cause diseases. Some of them are: total coliforms, fecal coliforms and enterococci.

To be a good indicator they must have a correlation with the pathogens and be more abundant than them. Its presence in a food indicates the possible presence  simultaneous pathogen microorganisms. For example, E. coli has been used as  Index of possible presence of pathogens of enteric origin in water and food