Compartment Bag Test (CBT) kits, developed by Aquagenx, are a simple tool that can be used to determine Escherichia coli (E. coli) most probable number (MPN) in a water sample. They have been suggested as a way to test drinking water quality in the Pacific Islands that is more informative than presence-absence tests whilst remaining suitable for situations where access to laboratory equipment and trained professionals are not available.
Although much is known about the use and accuracy of CBT kits within a laboratory setting, the limitations of their use by non-scientifically trained individuals in field settings is not covered in detail in the literature. Therefore, their ease-of-use for non-scientifically trained individuals and the accuracy of results as determined by such individuals should be understood prior to use of the CBT kits in Pacific Islands.
Members of a citizen science group who routinely monitor stream health by measuring physical and chemical parameters in a Christchurch river catchment were involved in field trials as they did not have any formal scientific training. Interpretation of the results following the “look-up table” provided with the CBT kits were found to be easily translated to E. coli MPN. However, there was variability in replicate samples especially when E. coli MPN was high. The results were broadly comparable with a reference method, Colilert Quanti-Tray 2000 analysed alongside the CBT kit trials. However due to both methods using Most Probable Number (MPN) methodology for enumeration, the range of quantification was quite large. Limitations to this investigation included the small sample size and replicates, analysis limited to stream water quality only and errors in field sampling.
This project allowed researchers to document a number of practical steps that could be taken to ensure the CBT kits perform at an optimal level.