Analysis of Cytotoxicity and Invasiveness of Heterotrophic Plate Count Bacteria Isolated from Drinking Water on Blood Media
An issue affecting all drinking water but in particular importance to bottled water, is the possible adverse health effects of naturally occurring microbes, collectively called heterotrophic plate count (HPC). HPC, are present in all bottled waters, even though the water may be subject to ozonation. The small numbers of HPC that survive ozonation multiply within the bottle to achieve concentrations in the thousands per ml. Tap water has fewer HPC per ml because it generally has a disinfection residual. In the late 1980’s, Dr. Pierre Payment (University of Quebec) presented data to indicate that HPC bacteria is responsible for gastroenteritis.
A laboratory based study was conducted by Dr. Stephen Edberg (Yale University) to isolate HPC from tap water and bottled water products. The HPC were isolated on blood agar and then subjected to a large battery of tests to determine if they possessed characteristics associated with human infection. These characteristics are known as virulence factors.
Major Findings and Significance
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 under- taken to estimate the health risk from these naturally occurring bacteria by the determination of cytotoxicity and invasiveness in a human enterocyte cell line. HPC bacteria were isolated from bottled and tap water samples by enumerating them under physical and chemical conditions analogous to human physiology. All HPC bacteria were examined at both log and lag phase of their growth cycles. Bacterial broth supernatants were also tested to serve as critical negative controls. Naturally occurring HPC bacteria demonstrated low invasiveness and cytotoxicity with more than 95 of isolates showing equivalency to broth supernatant. When showing either invasiveness or cytotoxicity, only a small number of cells from the culture were positive.
Edberg, S.C., Kops, S., Kontnick, C., and Escarzaga, M., Analysis of Cytotoxicity and Invasiveness of Heterotrophic Plate Count Bacteria (HPC) Isolated from Drinking Water on Blood Media, Journal of Applied Microbiology, 82:445-461 (1997).