Microbial Source Tracking

What is Microbial Source Tracking (MST)?

Microbial Source Tracking (MST) is a set of methods used to determine the host (different animals or Human) that contributes faecal pollution and microbial contamination to a variety of water bodies. Faecal pollution is a common problem that occurs in many water systems. When high counts of faecal bacteria are present in a water source, it poses a serious health risk for the public as well as economic losses for industries relying on coastal waters.

Application

The application of MST to risk assessment, total maximum daily load (TMDL) assessment or beach monitoring provides a tool for identifying the source of the pollution and allowing for appropriate remediation and preventative measures to be taken.

Faecal pollution can originate from point and non-point sources. Point sources may include sewage, effluent from wastewater treatment plants and stormwater. Nonpoint sources may include leaking septic systems, agriculture or wildlife runoffs where the entry point of contamination to surface waters is not obvious. Nonpoint sources are most apparent after storm events and are the cause of many water system impairments. If it is determined that the major contributor of the faecal pollution of a certain water system is Human, then compromised sewage or septic systems in the area should be the most probable cause. If the major contributor is cattle, then nearby farms should be suspected.

Microbial Source Tracking Tests offered

X = Available source tracking analysis    Q = Analysis can be quantified

Bacteroidetes Enterococcus Enterovirus Polyomavirus HUMAN COW   BIRD     DEER       PIG       GOOSE       CHICKEN       DOG       HORSE

C.Marimammalium  GULL

How does MST work?

In recent years, library-independent MST methods have rapidly displaced library-dependent MST methods which had multiple limitations and disadvantages. Library-independent approaches use molecular-based techniques to directly detect the genetic sequences of faecal indicator bacteria (FIB). The gut microbiota differs between animal hosts due to differences in animal digestive systems and microbial natural selection. It is expected that unique strains of FIB will exist only in their respective hosts. This allows for the identification of host faecal pollution by genetically detecting host-specific microorganisms. This is done with a technology termed quantitative Polymerase Chain Reaction (qPCR). qPCR targets regions of genes unique to each host-specific microroganism. The most targeted gene for MST use is the 16S rRNA gene. This gene is highly preserved but has variable regions that allow for the determination of the bacteria’s origin to the level of species or subspecies. The fact that it has numerous copies in a cell makes it easy to detect even when it is diluted in environmental waters. The most common FIB for the identification of livestock, Human and domestic pet sources are Bacteroides. They are obligate anaerobes, believed to be found predominantly in faeces, constitute approximately one third of the faecal bacterial population and exhibit host-specific variations. Other widely used FIB are Enterococci, Enterovirus, and the highly Human-specific Polyomavirus.

For a greater degree of certainty, it is recommended that multiple bacteria specific to a suspected host be examined when possible. For example, if a positive detect for Human-specific Bacteroides is supplemented with a positive detect for Human-specific polyomavirus, the strength of the test is increased providing a good indication that human faecal pollution is present in the water sample.