BACTEROIDALES: REVOLUTIONISING MICROBIAL SOURCE TRACKING
The age of using Escherichia coli and Enterococci sp. as standard faecal indicator bacteria is coming to an end.
B J Tillett, V Pettigrove
Publication Date (Web): 31 January 2017
Managers of recreational waterways are increasingly concerned with health risks associated with human faecal contamination. Currently Escherichia coli and Enterococci sp. are the standard indicators used to assess whether waters are safe for recreational activities. However, they are general indicators of faecal pollution from warm blooded animals and do not specifically indicate the presence of human faecal contamination. There is also growing evidence that certain strains of both E. coli and Enterococci sp. are able to propagate in external environments, reducing confidence that observed levels are truly representative of faecal contamination.
Bacteroides-Prevotella spp. is an abundant group of bacteria living in the gut of all warm blooded animals and therefore present in high concentrations in their faeces. It is now evident that for the most part, these bacteria are species specific and therefore can be used as a diagnostic signature for the origin of the faecal contamination, that is, human faecal contamination versus other animals such as dogs, cattle, pigs and birds which may also be important contributors to urban and rural water quality problems. These targeted indicator bacteria allow water managers to better source what animals are contributing to faecal contamination in waterways and consequently better predict human health associated with such contamination.
Bacteroides spp. assays, unlike standard measures of Escherichia Coli and Enterococci sp. amplify bacteria to quantifiable levels using genetic (quantitative polymerase chain reaction, qPCR) methodologies. These technologies use a suite of specific enzymes and thermo-cycles rather than bacterial viability. As such these new Bacteroides spp. assays quantify both viable and non-viable bacteria, increasing assay sensitivity compared with standard faecal indicator bacteria (FIB). Also, because the amplification of bacterium is measured per cycle during the qPCR process accurate determination of overall amplification efficiency and limits of detection and quantification can be calculated.
Water quality assessments that have included Bacteroides sp. assays have provided water managers with vital additional information on sources of contamination in waterways not available if only Escherichia coli or Enterococci sp. had been quantified. The greater sensitivity of Bacteroides sp. indicators has identified faecal contamination that was not detected by standard FIB. Also, Bacteroides sp. assays have discriminated bird and dog faecal sources of contamination identifying otherwise un-described non-point source contamination. And lastly, human-specific Bacteroides sp. markers have also been used to trace faecal contamination by identifying cracked sewers leaking directly into stormwater.
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