A Comparison of USEPA-Approved Enzyme-Based Total Coliform/E. coli Tests for Microbiological Groundwater Monitoring and Laboratory Consultation

Background/Need: Protection of groundwater from microbial contamination is a top public health priority. Recent epidemiological studies clearly show that gastrointestinal disease due to ingestion of drinking water is occurring at significant levels in the United States and Canada(1). Furthermore, the United States Centers for Disease Control reported in their last 10 year summary of waterborne disease outbreaks that over 70% of the documented outbreaks occurring in the U.S. were associated with contaminated well water (2). These facts underscore the need for sensitive, reliable laboratory methods to identify microbial contamination in groundwater that might pose a potential risk of illness. Since 2002, the United States Environmental Protection Agency (USEPA) has approved ten enzyme-based total coliform and E. coli detection tests for examination of drinking water. Differences in the ability of some of these methods to detect total coliform and E. coli, as well as suppress Aeromonas spp., a common cause of “false positive” results, have been observed. As a result, this study was undertaken to elucidate the strengths and weaknesses of each method.

Objectives: The objectives of the project were threefold; 1) to determine the capabilities of all of the USEPA approved products to detect the presence or absence of total coliform and E. coli in three chemically diverse groundwaters, 2) to determine the ability of each product to accurately quantify the number of total coliforms and E. coli in groundwaters, 3) to determine each product’s ability to suppress various concentrations of Aeromonas spp., which represent a noncoliform, heterotrophic bacteria likely to occur as a false positive interference (14,15).