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Microbial source tracing is a method used to determine the source of fecal pollution in a given environment in water.

It uses cultivable microbial indicators, for instance, bacterial host specific of bacteriophages related to human or animal fecal pollution sources; or host (human or animal) related genetic markers. MST allows not only the specific identification of this type of pollution (such as human sewage, animal waste, and agricultural or wildlife runoff) but also to take appropriate corrective actions to address or prevent this type of contamination.

So, MST can be used to study water quality in rivers, lakes, and other water bodies and to track the spread of pathogens in drinking water systems.

In the case of coliphages, MST can be used to identify the source of coliphage contamination in water bodies. Bacteriophages infecting some Bacteroides spp. strains proved high specificity to human or animal fecal pollution. These bacteriophages are viruses that infect and replicate within anaerobic bacteria present in warm-blooded animals and the human intestinal microbiome. Using these specific host bacterial strains or specific genetic markers also related to these human-associated Bacteroides bacteriophages (crAssphage), MST-developed predictive models can provide a correct determination of the origin of faecal water pollution.

Examples of microbial source tracing in water 

1. The use of abundance ratios of somatic coliphages and host-specific bacteriophages of Bacteroides spp. allows the detection and quantify the fecal origin of pollution.
2. Quantitative PCR based on specific molecular targets associated with the host can be applied in water samples for MST studies.
3. The combined application of multi-isotopic and molecular source tracking methods could be used to identify nitrate pollution sources in surface and groundwater.
4. The integrated analysis of traditional microbial indicators (such as E.coli or somatic coliphages) and some MST cultivable or molecular indicators showed to be also appropriate for resolving litigation MST matters.
5. Metagenomics based on specific host microorganisms (as is the case with bacteriophages within the group called crAssphage) may, in the future, be a method that analyses the genetic information of the entire microbial population of a water sample to identify the source of fecal pollution. 

When to implement a Microbial Source Tracing in water:

1. Collect samples from the water source and analyze them to identify fecal pollution origin.
2. Determine health risks associated with fecal-polluted water sources under potential fecal-oral pathogens.
3. Analyze the water samples for the presence of microbial markers mapping water resources in a particular geographic region.
4. Implement the necessary measures to reduce or eliminate fecal pollution.
5. Monitor the water source to evaluate the effectiveness of the measures taken.

Why is it important to track microbial sources in water? 

Microbial source tracking is an essential tool for determining sources of fecal pollution in water bodies. MST can be used to identify fecal sources from humans, livestock, and wildlife sources. By identifying sources of contamination, water managers can take steps to reduce pollution and protect public health. MST can also help detect the presence of fecal-oral transmitted pathogens that can cause disease in humans. Identifying and addressing sources of such pollution can help ensure that water resources are safe and clean for everyone.

Are coliphages a good indicator for microbial source tracking?

Yes, coliphages can be used as a traditional viral indicator for weighting the faecal pollution burden in an MST analysis. Coliphages are viruses that infect enteric bacteria and have been used to define predictive models of MST. Coliphages are easy to detect and quantify and help identify sources of fecal pollution in aquatic media. 

Who performs microbial source tracking, and what is it necessary for?

Microbial Source Tracing (MST) is usually performed by environmental scientists, public health officials, and other experts in the field of water quality. Determining the sources of bacteria, viruses, and other microorganisms in water systems is necessary to prevent waterborne disease outbreaks. Moreover, the determination of fecal sources is also important to take measures to mitigate any potential health risks associated with contaminated water. 

Microbial Source Monitoring campaigns conducted around the world

Microbial source tracking campaigns are usually conducted through laboratory and field monitoring methods. In the laboratory, microbial source tracking methods are used to identify and quantify the presence of specific indicator organisms that can be linked to a particular source of fecal pollution. Field monitoring involves collecting water samples at various locations to measure the concentrations of microbial indicators in the water and analyzing MST host-specific markers or indicators. These data can be used to define prediction models and develop strategies to reduce or eliminate this type of pollution.

Water regulations requiring microbial screening at the source: 

No, there are currently no water regulations requiring Microbial Source Tracing. However, some states, such as California and Florida, have adopted regulations requiring the implementation of certain types of source tracking programs. These programs typically focus on identifying sources of fecal pollution in surface waters and help inform management strategies to reduce water pollution.

Best techniques for conducting a microbial source monitoring campaign:

1. Implement a comprehensive monitoring program: This includes regularly testing water samples for traditional microbial indicators, such as coliphages, to identify possible sources of contamination.
2. Develop a comprehensive education and outreach program: This involves informing the public about the importance of proper hygiene, proper disposal of waste, and other contamination prevention strategies.
3. Implement a targeted sampling program: This involves collecting samples from suspected sources of fecal pollution and analyzing them for microbial indicators and other MST markers.
4. Use advanced technologies: This includes the use of DNA-based techniques, such as host-associated quantitative PCR, to identify specific sources of fecal pollution.
5. Establish an early warning system: This involves deploying predictive models and early warning systems, such as automated sampling devices, to detect potential sources of fecal pollution.
6. Develop an enforcement program: This involves enforcing laws and regulations related to source tracking and fecal pollution.
7. Develop a data-sharing program: This involves sharing data among agencies and departments to identify sources of fecal pollution and coordinate response efforts more effectively.