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RARE OCCURRENCE OF HETEROTROPHIC BACTERIA WITH PATHOGENIC POTENTIAL IN POTABLE WATER
Citation:
Stelma Jr., G N., D J. Lye, B G. Smith, AND J W. Messer. RARE OCCURRENCE OF HETEROTROPHIC BACTERIA WITH PATHOGENIC POTENTIAL IN POTABLE WATER. Presented at Joint Workshop-National Sanitation Foundaton/World Health Organization, Geneva, Switzerland, April 22-24, 2002.
Impact/Purpose:
The major objective of this project was to develop a statistically-based sampling plan that can be applied to determine the occurrence of heterotrophic bacteria in community distribution systems nationwide as well as individual household systems.
Description:
Since the discovery of Legionella pneumophila, an opportunistic pathogen that is indigenous to water, microbiologists have speculated that there may be other opportunistic pathogens among the numerous heterotrophic bacteria found in potable water. The USEPA developed a series of rapid in vitro assays to assess the virulence potential of large numbers of bacteria from potable water to possibly identify currently unknown pathogens. Results of surveys of potable water from several distribution systems using these tests showed that only 50 of approximately10,000 bacterial colonies expressed one or more virulence characteristics. In another study, 45 potable water isolates that were isolated from granular activated carbon filters and expressed multiple virulence factors were tested for pathogenicity in immunocompromised mice. None of the isolates infected mice that were compromised either by treatment with carrageenan, to induce susceptibility to facultative intracellular pathogens, or by cyclophosphamide, to induce susceptibility to extracellular pathogens. These results indicate that there are very few potential pathogens in potable water and that the currently developed in vitro virulence screening tests give an overestimation of the numbers of heterotrophic bacteria that may be pathogens. Current efforts are focused on using the animal models to screen concentrated samples of waters known to contain large numbers of heterotrophic bacteria and newly discovered Legionella-like organisms that parasitize amoebae.