Virulence and risk from drinking water of heterotrophic plate count bacteria in human population groups

Bacteria are natural inhabitants of all aqueous environments. The heterotrophic plate count is a means of assessing the concentration of these bacteria in foods, water, and water filtration systems. Methods vary, but are designed to enumerate bacteria that have evolved an environmental lifestyle. Most commonly, low nutrient, low ionic strength culture media are employed. The group of environmental bacteria enumerated depends on the media formulation and incubation conditions but are commonly known as heterotrophic plate count (HPC) bacteria; in Europe, this group is also referred to as autochthonous flora. While HPC inhabit an environmental niche, there has been concern that at some concentration they may be a human health risk. A review of the literature, including animal and human feeding studies, analysis of virulence factors, and outbreaks demonstrates that HPC bacteria as enumerated on HPC culture media have not been established as a human health threat at any concentration in drinking water or foods.