Microbial Source Tracking

What are indicator bacteria?
Identifying waterborne pathogens can be difficult, time-consuming, and expensive. USEPA recommends testing for surrogates of pathogens called indicator bacteria. Indicator bacteria live in the intestines of humans and other animals, so detecting these bacteria in water shows fecal pollution. Indicator bacteria are easier to enumerate and much cheaper to test than pathogens.

Currently, two fecal indicators are commonly used for water quality testing. Escherichia coli is a type of bacterium found in the feces of humans and other warm-blooded animals. Enterococci, which belong to the enterococcus, are two species (E. faecalis and E. faecium) commonly found in human intestines and feces. E. coli is used for freshwater, and Enterococci is used for marine waters. 

Can indicator bacteria identify sources of pollution?
Researchers have been using indicator bacteria since the 1900’s. Indicator bacteria cannot identify the sources of pollution they only confirm the presence of fecal matter in water. Today, more advanced technologies can detect fecal pollution in water. They can also quantify and identify the sources. These techniques use principles of molecular microbiology and are known as “Microbial Source Tracking” methods. What are the potential sources of water pollution?
Various sources can impact our recreational waters. Sewage and failing septic systems, livestock, wildlife, birds, and companion animals are some of these sources that pollute our beaches.

How do we detect these sources?
Researchers use microbial source tracking (MST) technique to identify the sources of pollution in recreational waters. Just like fingerprints can be traced back to a person, bacteria have specific characteristics that allow researchers to trace them back to their source (whether from humans, wildlife, farm animals, or pets).

MST attempts to match a microbe (e.g. bacterium) with a polluted site (e.g. beach or river) and a known source to suggest the origin of fecal pollution.  This can be achieved by testing a variety of target organisms using molecular methods such as quantitative polymerase chain reaction (qPCR).

At the IWH Labs, we use both traditional culture-based and DNA-based methods. In addition to quantifying fecal indicators, we can also identify the sources of pollution by targeting a diverse set of MST markers using USEPA-approved assays. 

Last updated: 12/16/2024