ANALYSIS OF CYTOTOXICITY AND INVASIVENESS OF HETEROTROPHIC PLATE-COUNT BACTERIA (HPC) ISOLATED FROM DRINKING-WATER ON BLOOD MEDIA

Heterotrophic plate count (HPC) bacteria are naturally present in all aqueous environments. These bacteria undergo multiplication cycles in drinking water, especially in closed containers (bottled water) or in tap water when chlorine levels are dissipated, such as in dead ends in water mains or household plumbing. A study was undertaken to estimate health risk from these naturally occurring bacteria by the determinat ion of cytotoxicity and invasiveness in a human enterocyte cell line. HPC bacteria were isolated from bottled and tap water samples by enume rating them under physical and chemical conditions analogous to human physiology. All HPC bacteria were examined at both log and lag phase o f their growth cycles. Bacterial broth supernatant fluids were also te sted to serve as critical negative controls. Naturally occurring HPC b acteria demonstrated low invasiveness and cytotoxicity with more than 95% of isolates showing equivalency to broth supernatant fluid. When s howing either invasiveness or cytotoxicity, only a small number of cel ls from the culture were positive. Of those that were positive, log ph ase HPC bacteria were significantly more cytotoxic and invasive than t hose from stationary phase. Bacterial broth controls demonstrated vari ed, but often marked, cytotoxicity.