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 degrees C or 35 degrees 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 x 10(5) CFU/cm(2) measured as heterotrophic plate count (HPC), and at the other materials the density reached 3 x 10(3) CFU/cm(2) on PE and PEX and 5 X 10(1) and 5 X 10(2) CFU/cm(2) on Cu pipes after 58 d at 15 degrees C. Biofilm HPC values were higher at 35 degrees C than at 15 degrees 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 1 VC 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 degrees 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.