Fecal coliform is a group of bacteria found in the intestines and feces of warm-blooded animals, including humans, livestock, and wildlife. These bacteria are utilized as an “indicator organism” for water quality monitoring. Their presence signals that the water has been contaminated with fecal matter and may contain harmful, disease-causing pathogens. Detecting fecal coliform provides an easy and cost-effective way to gauge the potential for serious health risks associated with waterborne diseases.
Where Fecal Coliform Originates
The journey of fecal coliform into the environment begins with the waste of warm-blooded creatures, which finds pathways into water bodies. Human sources are a significant contributor, primarily through failing septic systems that allow untreated sewage to leach into groundwater or surface water. Older cities with combined sewer systems can also experience overflows during heavy rainfall, dumping raw sewage directly into rivers and streams.
Agricultural practices introduce fecal matter into the ecosystem, especially from livestock operations. Runoff from feedlots or fields where manure has been spread carries bacteria into nearby waterways during storm events. Wild animal populations, such as deer, birds, and raccoons, naturally deposit waste that contributes to background levels of coliform bacteria. The detection of these bacteria indicates recent fecal contamination, making the water unsafe for certain uses.
The Health Risks of Fecal Contamination
Fecal coliform bacteria themselves are not pathogenic, meaning they do not typically cause disease. The danger lies in their co-existence with true disease-causing organisms, known as pathogens, which are shed in the same fecal matter. The presence of the indicator organism warns that viruses, protozoa, and pathogenic bacteria may also be present.
Pathogenic bacteria like Salmonella and E. coli O157:H7 can be transmitted through contaminated water. Waterborne viruses such as Norovirus and Rotavirus, along with protozoa like Giardia lamblia and Cryptosporidium, are commonly found alongside fecal coliform. Exposure to these pathogens can result in acute gastrointestinal illnesses, including diarrhea, vomiting, and abdominal cramps. More serious diseases like typhoid fever can also be spread through this route.
Testing and Regulatory Standards
Water quality experts rely on specific laboratory procedures to detect and quantify fecal coliform contamination. The results are typically expressed as the number of Colony Forming Units (CFU) or Most Probable Number (MPN) per 100 milliliters of water sample. The analysis often uses an elevated incubation temperature of 44.5°C to isolate the thermotolerant coliform group, a more specific subset of the total coliform group.
The terminology used in testing is distinct: Total Coliforms include bacteria found in soil and plants, while Fecal Coliforms are a specific indicator of warm-blooded animal waste. The species Escherichia coli (E. coli) is the most specific and reliable indicator, as it is found almost exclusively in the gut of warm-blooded animals. Regulatory agencies, such as the U.S. Environmental Protection Agency, have set standards for water quality based on these indicator organisms.
For public drinking water supplies, the standard for E. coli must be zero; any confirmed presence constitutes a violation requiring immediate action and public notification. Recreational water bodies, such as beaches and lakes, have different, less restrictive criteria since contact is not intended for consumption. For freshwater recreational sites, the EPA recommends that the geometric mean of E. coli concentrations should not exceed 126 CFU per 100 mL over a 30-day period. These regulatory thresholds protect public health by minimizing the risk of waterborne illness.