Limitations of library-dependent microbial source tracking methods

Over the past 15 years, microbial source tracking (MST) methods have emerged as a management tool for water quality authorities to identify the sources of faecal contamination in receiving waters. The majority of the MST methods require the development of a library of target strains or faecal indicator bacteria from suspected sources by using various genotypic or phenotypic methods. Phenotypic or genotypic patterns of target strains are then compared to the library to identify their likely sources. None of these library-dependent methods are regarded as a 'gold standard'. Significant limitations include the size and representativeness of the developed library, temporal and geographical stability of target strains, host specificity of target strains, relative persistence of target strains in receiving waters and differences in statistical methods used. This paper reviews the various assumptions and limitation of library dependent methods currently used for source tracking