Animal and wildfowl only sources suspected

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Animal and wildfowl only sources suspected

When the site survey has been completed and the likely source of contamination identified is animals or birds, 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. 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. If the waterway is in a rural agricultural area where sheep and cattle/cows graze close to the waterway then it may be useful to begin with the two PCR markers that identify herbivores and are based on the detection of faecal contamination from sheep and cattle. At this stage there is no published PCR marker to distinguish between sheep and cows. At present the only bird PCR marker available was designed to detect duck contamination but has also been identified in swans and Canada geese so can be an indicator of wildfowl pollution.

Faecal Sterol analysis may be a useful adjunct to the PCR assays for herbivore contamination and we are currently developing further sterol analysis to identify other animals such as possums, dogs and birds. 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.

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.