Heterotrophic Plate Count (HPC) Bacteria - What is their Significance in Drinking Water?

THE ISSUE

While the literature documents the universal occurrence of HPC bacteria in soils, foods, air, and all sources of water, there is a lingering question as to whether this group of organisms may signal an increased health risk when elevated populations are present in drinking water. This paper reviews the relevant literature on HPC bacteria in drinking water, the lack of clinical evidence that elevated populations or specific genera within the HPC flora pose an increased health risk to any segment of the population, and the appropriate uses of HPC data as a tool to monitor drinking water quality changes following treatment. It finds no evidence to support health-based regulations of HPC concentrations.

RESEARCH STRATEGY

A peer reviewed scientific research paper was prepared to examine the significance of Heterotrophic Plate Count (HPC) bacteria in drinking water.

MAJOR FINDINGS AND SIGNIFICANCE

While the literature documents the universal occurrence of HPC bacteria or autochthonous flora in soil, food, air, and all types of water, there is insufficient clinical and epidemiological evidence to conclude that HPC bacteria in drinking water pose a health risk. For this reason, it is not possible to establish health-based standards for HPC bacteria in drinking water. The various methods used to enumerate HPC bacteria differ significantly in the number and genera detected, and HPC data from different methods are not necessarily comparable. HPC populations greater then 500-1000 cfu/mL in drinking water can interfere with coliform/E. coli analysis by lactose-based methods, which include the membrane-filtration method. Klebsiella, Pseudomonas, and Aeromonas cannot be considered opportunistic pathogens when found in drinking water, since there is no clinical or epidemiological evidence to support this designation. HPC determinations can be a useful tool to the monitor efficacy of drinking water treatment processes and undesirable changes in bacterial water quality during storage and distribution, but not because of health-risk reasons.

Allen, M.J., Edberg, S.C., and Reasoner, D.J., Heterotrophic Plate Count (HPC) Bacteria-What is Their Significance in Drinking Water?, April 2002, submitted for publication in the International Journal of Food Protection.

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