A recent study tracking the source of faecal contamination in waterways is providing useful information to those who manage these precious resources, reaffirming current routine testing tools are still effective for monitoring water quality.
The study, conducted by a team of PHF Science water quality scientists and led by AgResearch (now the New Zealand Institute of Bioeconomy Science), sought to differentiate between the different types of Escherichia, a genus of bacteria that includes E. coli, some of which can cause serious illness.
E. coli is found in the intestines and faeces of humans and warm-blooded animals, so water monitoring tools, such as the globally accepted Colilert test, look for its presence to indicate that faecal pollution has occurred.
But recent research indicates some ‘naturalised’ faecal E. coli strains can survive and potentially reproduce outside an intestinal environment. In addition, there are non-E. coli Escherichia bacteria that are indistinguishable from faecal-derived E. coli by routine water monitoring tools. This led regional councils to question if routine water testing was still an effective way of confirming if a waterway had been polluted.
The study involved genetic work to discriminate between the different types of Escherichia. Paired samples were collected from waterways within pristine native bush and compared with samples from waterways downstream of the pristine sites and impacted by urban or agricultural sources. Escherichia were isolated from a total of 413 samples from water, soil, sediment, biofilm, and faecal samples (avian, livestock, feral animals) and evaluated to determine which type they were.
The findings showed that in impacted waterways, E. coli was more prevalent, whereas in pristine waterways, non-E. coli Escherichia, and in particular, a recently identified type called E. marmotae, was more prevalent (although well below the threshold outlined by water quality guidelines).
This gives assurance that routine water quality monitoring tools, such as the industry standard Colilert test, are still appropriate for identifying faecal contamination in impacted waterways.
The study was supported by a MBIE Smart Idea project on faecal source tracking and Escherichia coli in recreational waters, and was a collaboration between the New Zealand Institute of Bioeconomy Science as the contract holder, PHF Science, Massey University and NIWA (now part of the New Zealand Institute for Earth Science). Further research is required to clarify whether non-E. coli Escherichia represent a health risk to humans when identified in water sources.
The study adds to the body of evidence about naturalised/environmental Escherichia species by contributing to research by PHF Science into human-health impacts associated with freshwater environments.