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:

Heterotrophic bacteria (HPC) are common to community distribution systems conveying treated drinking water to consumers. There are known opportunistic pathogens among these organisms, for example some Legionella and some Aeromonas strains; and there may be others of which we are currently unaware. The occurrence and extent of exposure to these bacteria are unknown either at the community level or the national level. At the present time no statistically valid sampling plan is available to determine how many samples must be examined to measure the occurrence of particular types of microorganisms within a community or how many communities must be examined to measure nationwide occurrence. This is because we don't know the variability either in the total numbers of HPCs or in the variety of HPCs that occur within a community, or even within a single building. This project addressed the need for determining the frequency of sampling, the number of sampling sites and the total number of samples per site needed to get an accurate estimate of the occurrence of levels of total heterotrophic bacteria or of specific types of heterotrophic bacteria in household distribution systems. One product of this project is the formation of a statistically valid sampling plan. The key to developing a sampling plan is to determine the variability in numbers and types of bacteria first within a household system then among households within a community. Once the variability is known it will be possible to calculate the number of sampling sites and total number of samples needed to get an accurate representation of occurrence. For this project, the term "household" referred to any system beyond the main distribution system. Household systems may be as simple as single residential systems or as sophisticated as multi-story hospital systems. Sampling occurred year-round to demonstrate the variations in heterotrophic bacterial counts and colony morphology and expression of certain virulence-related characteristics typical to these types of distribution systems. The heterotrophic bacteria frequency of occurrence from a single building within a community system had already been determined. Sampling of heterotrophic bacteria in the community system surrounding the building was performed for comparison. The data from these samples will be used to develop a statistically-based sampling plan for community systems.

Record Details:

Record Type:PROJECT

Start Date:10/01/1998

Completion Date:09/30/2002

Record ID: 18286

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Project Information:

Progress :The project is completed. Occurrence data were collected for one building within a local community to determine the variability in occurrence of various types of HPC bacteria within one building using membrane filter methodology and growth on R2A medium (25 C) and PCA medium (35 C). Bacterial isolates were categorized into (A) rapid growing and forming white colony, (B) slow growing and forming yellow pigmented colonies, and (C) slow growing and forming pink pigmented colonies. Key virulence characteristics were also examined. The study was expanded to examine the variability in occurrence among different buildings within the same community. We now have occurrence data for bacterial heterotrophs in drinking water samples from a total of four multi-story buildings over a period of 24 months. Preliminary statistical analysis is being performed to determine any significant factors concerning the bacterial populations monitored in these studies.

Relevance :Epidemiological evidence suggests that exposure to heterotrophic bacteria that occur naturally in potable water is not a risk to the healthy population. However, it is unclear whether these organisms pose a significant health threat to vulnerable sub-populatins, such as the very young, the elderly and the immunocompromised. In addition, high heterotrophic bacteria levels would represent the presence of significant biofilm material in the distribution system pipes. Other bacteria, known to be human pathogens (e.g. Aeromonas spp. and Mycobacterium avium) find protection from disinfectants and can replicate in such biofilm material. Therefore a better understanding of heterotrophic bacteria levels in drinking water systems will be useful in determining the potential for the occurrence of human pathogens. There will be two significant applications of this data to existing community water distribution systems. The first is the development of a sampling plan that will assure the best possible estimate of heterotrophic bacteria, including those on the CCL, within all the various microcosms of a single distribution system. This sampling plan will be used by OGWDW and ORD scientists to guide future occurrence studies of specific CCL pathogens, as it is not yet possible to continously monitor for pathogens in drinking water. The information obtained from occurrence studies will in turn aid OGWDW in determining whether a need exists to regulate those pathogens on the CCL. The second impact will be on the development of new modeling programs for water quality within existing distribution systems. Opportunities exist for future collaboration with other ORD groups (e.g. NRMRL) who are involved in the use of modeling to assess water quality problems in drinking water distribution systems.

Clients :Dr. Paul Berger, OGWDW

Research Component :M/DBP (MICROBIAL)

Risk Paradigm :EXPOSURE

Project IDs:

ID Code :EX.M.15

Project type :ORD-DW Plan

ID Code :378

Project type :OMIS