Characterization of bacterial coliform occurrences in different zones of a drinking water distribution system.

AIMS: To compare the bacterial coliforms detected from occurrences in three zones of a water distribution system supplied by two separate water sources. METHODS AND RESULTS: Conventional and standardized protocols for identifying enterobacterial populations were applied. Additional tests to confirm isolates were included. Analyses of diversity and population similarity were performed using the Phene Plate System, a miniaturized biochemical phenotyping method. Isolates were identified by the API 20E system in tandem with biochemical phenotyping. A total of 16 576 samples were taken from the water distribution system, with 1416 isolates analysed. A low number of coliform occurrences were observed (2%). Escherichia coli was not detected in either water origin or in Zone 2 samples; however, in Zones 1 and 3 a low number of cases of E. coli were recorded. The percentages of E. coli depended on the identification criteria. Eight biochemical profiles for coliform populations were defined according to the results of the confirmative tests. There was a high diversity among these populations in the three zones studied, although no significant variations in their composition (associated with occurrences in the different zones) were observed. Klebsiella oxytoca was the most commonly detected species irrespective of zone, although seven other enterobacterial genera were also found. CONCLUSIONS: Analysis of the enzymatic activity of beta-glucuronidase or application of the criteria established in the norm ISO 9308-1, in tandem with thermotolerance was needed to evaluate the occurrence of E. coli in the distribution systems. Detected occurrences of bacterial coliforms could be associated with re-growth patterns for specific sampling points in the distribution system. Seasonal differences, independent of the studied zones, were observed. SIGNIFICANCE AND IMPACT OF THE STUDY: Biochemical phenotyping of bacterial coliforms was shown to be a useful method on the characterization of occurrences in water distribution systems.

The Pseudomonas group as an indicator of potential regrowth in water distribution systems.

The regrowth of micro-organisms in the water distribution system is assisted by the presence of biodegradable organic matter (BDOC). The low concentration of available organic carbon in this type of water favours the growth of bacteria belonging to the Pseudomonadaceae family, as this group can grow better at low concentrations of substrate than other bacteria also present in the distribution system. Although the genus Aeromonas has already been adopted as an indicator of this potential regrowth, members of the Pseudomonadaceae have not yet been proposed as indicators of potential bacterial regrowth in the water distribution system. The results are presented of a year-long study of the Barcelona distribution system in which the presence of Pseudomonas and Aeromonas was analysed and the validity of these micro-organisms as indicators of potential regrowth in the distribution system was assessed. It seems that, at least in the drinking waters of the Barcelona area, Pseudomonas is a better indicator of potential bacterial regrowth than Aeromonas.