Microbial Source Tracking Analysis

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Risk assessment of drinking water supplies for the likely occurrence of pathogenic organism has, for many years, focused on the detection of total coliforms, faecal (or thermotolerant) coliforms, and more recently E. coli as primary indicator of potential faecal contamination. However, outbreaks have occurred in the absence of these microbial indicators, highlighting the need for a multifaceted approach for risk assessment in drinking water supplies.

Microbial Source Tracking (MST) combines physical, chemical and biological diagnostic tests to characterize the level and source of potential faecal contamination. It provides the opportunity to add valuable information to investigations of water supplies and catchment areas.

Recent development of MST has focused on the molecular detection of strains of the bacteria Bacteroides, which can differentiate between human and some animal sources of pollution. Previous studies have found that human faecal contamination poses a greater risk to human health than contamination from other faecal sources.


GHD in conjunction with several Melbourne water utilities and the Victorian Smart Water Fund, examined human- and ruminant-specific MST methods using Bacteroides markers. Methods were used to examine stormwater and urban waterway sites in parallel with other water quality parameters. On the basis of this trial, the use of this suite of parameters appears promising, and methods identified throughout this process have now been made commercially available.

The Bacteroides MST tests were used to give a qualitative assessment of the likelihood of human or ruminant faecal contamination being present. The methods applied were likely to be applicable to a variety of situations; such as determining pathogen hazards to bathers in recreational waters, or evaluation of source waters for treatment, or for tracing the origins of contamination in catchment studies.

This research identified that a tiered approach can be applied when using MST methods. This involves initially performing a suite of routine water quality tests (MST1), to screen sites and identify locations requiring further investigation using the Bacteroides parameters (MST2).

With the ability to determine the origin of the microbial contamination, MST is a powerful tool that can be used for:

  • urban stormwater investigations, where its use as a source water requires treatment before use in fit-for-purpose applications. Determining the level of treatment requires assessment of the hazards involve; with pathogen hazards dependent on the origin of contamination
  • catchment studies where identification of sources of sporadic contamination are frequently required, enabling remedial action and protection of supply
  • assessment of environmental waters used for recreation or aquaculture which are sensitive to the impacts of sewage pollution. MST can be used in site risk assessment and in the investigation of contamination incidents in these locations

MST techniques based on Bacteroides are starting to be used to guide major expenditure decisions and regulatory action regarding sewage disposal in the United Kingdom and substantial studies using these methods are taking place around the world.

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