Impact of Pipe Materials and Chlorination on Planktonic and Biofilm Cells of Listeria monocytogenes

This work aimed to determine the influence of different chlorine doses to inactivate of Listeria monocytogenes biofilm cells collected from six types of pipe materials, which are commonly used in household at different biofilm ages. A laboratory-scale simulated distribution system, that consists of a design based on six different pipe materials which are: polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), iron (I), copper (Cu) and rubber (R). Six samples of L. monocytogenes biofilm were collected from the previous designed system at three different biofilm ages (10, 40 and 90 days-old). The collected biofilm samples were exposed to different chlorine doses (0.2, 0.6, 1.0, 1.4, 1.8, 2.2, 2.6 and 3.0 mg/l) at 10 min, and then total bacterial counts using pour plate method was enumerated. The results showed that the log reduction of 90 days-old of L. monocytogenes biofilm formation, when exposed to 3.0 mg/l of chlorine dose, on six pipe materials; PVC, PP, PE, I, Cu and R was 3.96, 4.16, 4.21, 4.17, 4.32 and 4.03 CFU/cm 2 , respectively with the initial count of biofilm cells was 10 6 CFU/cm 2 . While the log reductions of L. monocytogenes planktonic cells were: 6.20 CFU/ml (complete reduction) at the same dose of chlorine dose. The present study concluded that the biofilm cells are more resistant to chlorine dose than planktonic cells. Moreover, the biofilm of 10 days-old is more sensitive than 40 days-old followed by 90 days-old that grows in different pipe materials. In addition, chlorine effectiveness depends on its concentration, the exposure time, nature of pipe materials and the age of biofilm.