Microbial Source Tracking (MST)

The Main Points

  1. MST is a useful management tool for long-term watershed management because it can help identify sources of fecal contaminations.
  2. MST relies on known host-specific DNA markers to pinpoint where the fecal contaminations come from.
  3. Polymerase Chain Reaction (PCR) and Real-time PCR (qPCR) enable us to detect and quantify a tiny amount of DNA markers in the environment, but these analysis can only be performed in the laboratory.

The Details

Microbial Source Tracking (MST) is a laboratory analysis that complements Fecal Indicator Bacteria (FIB).  It can help to identify potential sources of fecal contamination and provide insights to identify the origins of non-point source pollutions, such as stormwater runoffs and septic systems. Knowing which of the sources are contributing to fecal contamination can help develop effective reduction strategies.  MST has been recommended by the U.S. Environmental Protection Agency as a tool for overall watershed management.

Fecal bacteria are often uniquely adapted to their hosts.  In MST, we look for particular fecal bacteria that are associated with specific hosts. By taking advantage of certain traits in these fecal bacteria, we would be able to tell what the hosts are and thus where the fecal contaminations come from. One of the traits of fecal bacteria is unique DNA sequences, which is referred to as “DNA markers.”  There are known markers for humans, domestic animals (dogs, pigs, cow and horse), and wildlife (Canada geese and deer). 

In the natural environmental, host-specific DNA markers often exist in a tiny amount. Polymerase Chain Reaction (PCR) multiplies DNA markers to an amount that can be easily detected. In addition, Real-time PCR (qPCR) enables us to quantify the original tiny amount of DNA markers in the environment. Because these require specialized equipment and experienced scientists to conduct analysis, it is important to work with the laboratory personnel to generate accurate results to develop appropriate watershed management strategies.