Bacteroides species as indicators of faecal pollution in environmental water sources: a literature review
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Faecal pollution of water has long been an issue of great concern due to the potential health risks associated with faeces. A lack of understanding the implications of sewage contamination in water combined with inadequate municipal management practices contribute toward deterioration of water infrastructure. Poor management practices, particularly in developing countries, combined with limited financial resources restrict the extent of water quality monitoring which takes place, especially in rural areas. Recent large-scale sewage contamination of the Vaal River in South Africa is an example of where microbial source tracking (MST) by means of Bacteroides host-associated assays could be applied advantageously in mitigation efforts. Bacteroides species make up the majority of mammalian intestinal bacterial communities. The intestinal community composition of hosts may however still vary regionally and per individual due to factors such as diet. Unlike conventionally applied faecal indicator bacteria (FIB), Bacteroides has very limited survival capabilities in the environment due to their anaerobic nature. Subsequently by detection of the host source and quantification of marker levels the extent of contamination as well as possible points of entry into an area of interest may be determined. Unfortunately, as with any developing technique, increased popularity and frequency of application have brought several shortcomings of Bacteroides related assays to light. A systematic literature review was performed identifying recurring themes with regard to challenges and limitations faced by researchers applying Bacteroides related assays to environmental water samples. It is evident from the literature that a lack of marker specificity both by host species and geographically hinders the application of these techniques worldwide. Markers that were thought of as host-specific were frequently detected in other animal host groups in the reviewed literature. Another shortcoming of these techniques is sensitivity to inhibitory substances commonly found in faeces and environmental water. Data interpretation according to different parameters such as a set sample volume regardless of DNA concentration or DNQ (detected but not quantified) samples in quantitative PCR assays being seen as either positive or negative may complicate data comparability between datasets or across similar studies. Cost reduction of these techniques will increase the opportunities for application in developing countries. These methods are best applied in a toolbox approach along with several other assays or markers in order to estimate the full extent of contamination in a sampling area. Standardisation of Bacteroides host-associated assays is crucial for successful application of these techniques, especially with regards to comparability of data.