A retrospective analysis of coliform events in a drinking water distribution system was conducted. A total of 13 coliform isolates with specific geographic/sampling records were analysed using microbial source tracking (MST) to establish genetic (based on DNA) and phenotypic (based on substrate utilization) relatedness between isolates, and a data integration approach (geo-spatial and event analysis) to identify potential causes for their presence. Phenotypic analysis, using the API® 20E system, identified two major genera: Enterobacter and Citrobacter, showing a high degree of phenotypic similarity within each species. However genotypic analysis (using pulsed field gel electrophoresis) of the Enterobacter and Citrobacter isolates demonstrated a wide genetic diversity within each species. The data integration approach revealed the probable causes for coliform events were the installation of new mains (8 samples) and rehabilitation of existing main (1 sample). The data integration and MST approach (genotyping) suggested that these coliform events were a result of sporadic intrusion from maintenance events and not chronic biofilm re-growth. The combination of MST and the data integration approach offers utilities a potentially powerful tool for the examination and determination of coliform occurrences in a distribution system.

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