ABSTRACT
All tested materials were rapidly colonized by bacteria, but the population densities varied significantly. The highest total cell count was measured on PE-HD and PVC at the granulated activated carbon (GAC) filter. The total counts were about 2.5 X 106 (± 5 .0 X 105) cells cm -2 for both materials af ter 9 days of incubation (Figure 1). In contrast to the plastic materials, metal coupons were colonized in lower density. Stainless steel coupons were colo nized with 1.3 X 106 (±3 .0 X 105) cells cm 2, whereas on copper a total cell count of 5.0 X 105 (±5 .0 X 104) cm -2 was measured after 9 days incuba tion at GAC. After disinfection (DIS) the total cell counts on all materials were reduced. One order of magnitude less cell counts were determined on plastic materials at the sampling point DIS (4.0 X 105 cells cm -2 ), on steel the bac terial cell count was about 3.0 X 105 (±4.5 X 104) cells cm -2 and 4.2 X 104 cells cm -2 on copper. Despite the reduction of the bacterial cell count by chlo rine dioxide, a biofilm formation within the distribution system (D l, D2) was observed during the short incubation time of 12 days (D l) and 15 days (D2). Again, there was a dependence on the used substrata. Plastic materials reach ing a cell density in an average of 1.2 X 106 (±2.5 X 105) cells cm -2 . In comparison with PE-HD and PVC, the analysis of metal coupons at D l and D2 showed again reduced microbial density (3.3-6.9 X 105 cells cm -2 ).
