About Microbial Source Tracking

The lack of appropriate methodology for tracing bacterial contamination in the environment is a major impediment in identification and control of the sources of these pollutants and adversely affects the decision-making process in water-quality and management. Several methods namely ribotyping, pulsed field gel electrophoresis, antibiotic resistance analysis, rep-PCR, and carbon source utilization for tracking genetically engineered microorganisms have been used, but their utility is limited to the detection of organisms carrying reporter genes or their products. Limited efforts to track sources of natural bacterial populations have been made; the approaches used were based on quantification of indicator organisms at various sites; however, these studies invariably have raised more questions than answers.

Methodology that is successful in identifying sources of microbial pollution is called Microbial Source Tracking (MST). The specific methodology was developed by the Principal of the IEH Laboratories & Consulting Group, Dr. Mansour Samadpour. MST methodology has now been used in more than 80 studies around the country and in Canada. This validated tracking system for identification of sources of microbial pollution can be used to identify and assess the impact and contribution of non point sources of microbial pollution and to establish and characterize the impact of the point sources of microbial pollution in fecal runoff.

The method can be used to identify the sources of fecal coliforms at the species level and map their distribution, transport, and movement in watersheds, rivers, lakes, and drinking-water-distribution systems. Microbial source tracking (MST) studies have been conducted by Institute for Environmental Health, Inc., in closed watersheds, swimming beaches, and industrial wastewater-treatment plants.

Principles of MST

MST is based on the use of a genetic fingerprinting of Escherichia coli strains isolated from water and source samples by a method of ribotyping modified by Dr. Samadpour, termed Eco RI / Pvu II variant.

It is the DNA fingerprint of the E. coli that lives within the animal that is typed-not the DNA of the specific animal. Though fecal coliform bacteria found in many animal species are very similar genetically, there are differences among members of the same species that have adapted to live in different host species. It is thought that these distinctions in bacteria occur because the intestinal environments differ between animals, including humans.

It is in identifying these genetic differences that it is possible to associate bacteria with sources. In order to be successful with any type of microbial source tracking methodology, it is necessary to build a library of isolates from known sources. Isolates from the database library of known sources are matched or associated with the environmental samples collected. The larger and more diverse the library, the more likely a match can be made. IEH, Inc. has a library of approximately 120,000 source isolates used to accomplish such investigations.