Human only sources suspected

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Human only sources suspected

When the site survey has been completed and the likely source of contamination identified is human then the initial step is to sample and identify if there are elevated levels of E. coli present in the sample. Elevated levels of E. coli are dependent on the water type e.g. for bore water any E. coli present should initiate an investigation into its sources. When dealing with recreational waterways we have found that >200 CFU/ml of E. coli is likely to illicit useful information from the toolbox of assays. However, we have also been able to identify faecal sources when 50 CFU/ml was the level of E. coli in the water sample. So based on the need for an answer it may be worthwhile for water managers to trial a low E. coli level with the realisation that levels of contaminants may be too low for detection.

The initial test in the toolbox is DNA extraction and three PCR markers. The total Bacteroidetes is a useful detector of faecal pollution but does not identify animal hosts. Human contamination should be confirmed with FWA analysis using the quantitative method of HPLC. If time and money allow, then faecal sterol analysis can also be performed to give a higher level of confidence in the results for human pollution. In general, levels of E. coli should be >500 CFU/ml in a water sample otherwise faecal sterols may not be detected in adequate quantities to allow for data analysis of sterol ratios. A combination of all three of the assays: FWA, PCR markers and Faecal Sterol analysis is required to give a high certainty of the correct identification of a faecal source host. n the Total Bacteroidetes PCR marker is negative

Where the initial PCR markers are negative for total Bacteroidetes and human or animal and bird markers it is suggestive that the E. coli is not due to a recent faecal event. Where E. coli levels are persistently high but this is not supported by other faecal indicators from the toolbox, it may be worthwhile to investigate whether the E. coli is persisting in the environment. Certain strains may be able to survive in favourable environments such as sediments for long periods. It is not well understood if E. coli is able to replicate (grow) in the temperate environment of New Zealand, although there is evidence to suggest replication in tropical and subtropical environments. The identification of E. coli in the water column without further evidence for recent faecal contamination events is an on-going research area of particular interest to water managers dealing with the potential health hazards for recreational waterways and shellfish industries. Subtyping of the isolates of E. coli identified in water can indicate if there is a predominance of one or two subtypes which may indicate that those strains are surviving outside of an animal host for longer periods than most E. coli subtypes. If subtyping reveals multiple types of E. coli than this may confirm that there are multiple inputs of E. coli from animal hosts into that environment. When dealing with this issue it is necessary to talk through the potential routes of investigation with the water scientists at ESR.