<unk>  are types of<unk>  used to detect and estimate the level of fecal contamination of water. They are not dangerous to human health but are used to indicate the presence of a health risk. Each gram of human feces contains approximately ~100 billion ()<unk> . These<unk>  may include species of pathogenic<unk> , such as Salmonella or Campylobacter, associated with gastroenteritis. In addition, feces may contain pathogenic viruses, protozoa and parasites. Fecal material can enter the environment from many sources including waste water treatment plants, livestock or poultry manure, sanitary landfills, septic systems, sewage sludge, pets and wildlife. If sufficient quantities are ingested, fecal pathogens can cause disease. The variety and often low concentrations of pathogens in environmental waters makes them difficult to test for individually. Public agencies therefore use the presence of other more abundant and more easily detected fecal<unk>  as<unk> s of the presence of fecal contamination. Aside from<unk>  being found in fecal matter, it can also be found in oral and gut contents. Criteria for<unk>  organisms== The US Environmental Protection Agency (EPA) lists the following criteria for an organism to be an ideal<unk>  of fecal contamination: # The organism should be present whenever enteric pathogens are present # The organism should be useful for all types of water # The organism should have a longer survival time than the hardiest enteric pathogen # The organism should not grow in water # The organism should be found in warm-blooded animals’ intestines. None of the types of<unk>  organisms that are currently in use fit all of these criteria perfectly, however, when cost is considered, use of<unk> s becomes necessary.
Indicator bacteria
Multidrug-resistant bacteria
Pathogenic bacteria
Microgenia
PLOS Pathogens
Enteric bacteria 
Biofilm
Tocolytic