Effect of temperature and pipe material on biofilm formation and survival of Escherichia coli in used drinking water pipes: a laboratory-based study

Segments of used drinking water pipes of galvanised steel (GS), cross-linked polyethylene (PEX), copper pipes (Cu) or new medium-density polyethylene (PE) were investigated for the formation of biofilm and survival of E. coli in biofilm and in the water phase. Pipes were filled with water and incubated at 15 °C or 35 °C under static conditions. Biofilm formation was followed during 32, 40 and 56 (58) d. The most dense biofilm was formed on GS, reaching approximately 4.7×10⁵ CFU/cm² measured as heterotrophic plate count (HPC), and at the other materials the density reached 3×10³ CFU/cm² on PE and PEX and 5×10¹ and 5×10² CFU/cm² on Cu pipes after 58 d at 15 °C. Biofilm HPC values were higher at 35 °C than at 15 °C, with only slightly higher values on the metals, but 100-fold higher on PE and PEX. Adenosine triphosphate (ATP) measurements confirmed the general trends observed by HPC. Higher temperature was seen to be an important factor reducing E. coli survival in the water phase in drinking water pipes. At 15 °C E. coli survived more than 4 d in GS and Cu pipes and 8 d in PE pipes, but was not detected after 48 h at 35 °C. The E. coli survived longer at both temperatures in the glass control bottles than in the drinking water pipes. Despite the obvious biofilm formation, E. coli was not detected in the biofilm at any of the investigated surfaces.