Microbial Source Tracking: Current Methodology and Future Directions

Abstract

Maintenance of the microbiological quality and safety of water systems used for drinking, for recreating, and in the harvesting of seafood is imperative, as contamination of these systems can exact high risks to human health as well as result in significant economic losses due to closures of beaches and shellfish harvesting areas. Waters contaminated with human feces are generally regarded as a greater risk to human health, as they are more likely to contain human-specific enteric pathogens, including Salmonella enterica serovar Typhi, Shi- gella spp., hepatitis A virus, and Norwalk-group viruses. Ani- mals can also serve as reservoirs for a variety of enteric patho- gens (e.g., various serotypes of Salmonella, Escherichia coli, and Cryptosporidium spp.). Understanding the origin of fecal pollution is paramount in assessing associated health risks as well as the actions necessary to remedy the problem while it still exists. Traditional and alternative indicator microorgan- isms have been used for many years to predict the presence of fecal pollution in water; however, it is well established that the majority of these organisms are not limited to humans but also exist in the intestines of many other warm-blooded animals (55). Due to the ubiquitous nature of these organisms, the effectiveness of using traditional indicators to predict the pres- ence of human or animal waste impact and subsequent health risks is limited. The usefulness of the microbial indicators as tools for risk assessment can be significantly enhanced by the development of testing methods and analysis techniques that can define specific sources of these organisms. The concept that the origin of fecal pollution can be traced using microbiological, genotypic, phenotypic, and chemical methods has been termed microbial source tracking. This work will provide an overview of microbial source tracking methods that are currently being used to predict and identify sources of fecal pollution in the environment as well as provide insight into future directions in the field. MICROBIAL INDICATORS OF FECAL POLLUTION Indicator microorganisms are used to predict the presence of and/or minimize the potential risk associated with patho- genic microbes. Indicator organisms are useful in that they circumvent the need to assay for every pathogen that may be present in water. Ideally, indicators are nonpathogenic, rapidly detected, easily enumerated, have survival characteristics that are similar to those of the pathogens of concern, and can be strongly associated with the presence of pathogenic microor-