Journal of Water and Health Vol 5 No 2 pp 267-282 © IWA Publishing 2007 doi:10.2166/wh.2007.008

A comparison of ten USEPA approved total coliform/E. coli tests
Jeremy Olstadt, James Jay Schauer, Jon Standridge and Sharon Kluender
Water Bacteriology Department, Wisconsin State Laboratory of Hygiene, 2601 Agriculture Dr., P.O. Box 7996,
Madison, WI 53707-7996, USA Tel.: 608-224-6262Fax: [email protected]
Environmental Chemistry and Technology Program, University of Wisconsin-Madison, 600 N. Park Street, Madison,
Environmental Health, Department - Water Bacteriology, Wisconsin State Laboratory of Hygiene, University of
Wisconsin-Madison, 2601 Agriculture Drive, Madison, WI 53718, USA


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. These tests include: Colilert®, Colilert-18®,
Colisure®, m-Coli Blue 24®, Readycult® Coliforms 100, Chromocult®, Coliscan®, E*Colite®, Colitag™ and MI
Agar. The utility of the enzyme based test systems is based on both the ability of the test to detect the target
organisms at low levels and the ability of the test system to suppress the growth of non-target organisms that might
result in false positive results. 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. Water samples were
collected from three geographically and chemically diverse groundwaters in Wisconsin. One-hundred milliliter
aliquots were individually spiked with both low concentrations (one to ten organisms) and high concentrations (fifty
to one-hundred) of each of five different total coliform organisms (Serratia, Citrobacter, Enterobacter, E. coli, &
Klebsiella). These spiked samples were used to test the capability of ten enzyme-based test systems to both
detect and enumerate the spiked organisms. In addition, 100 ml samples were independently spiked with two
different strains of Aeromonas spp. at six different levels, to assess the ability of each enzyme-based test to
suppress Aeromonas spp. Analysis of the data indicated that wide variability exists among USEPA approved tests
to detect and quantify total coliforms, as well as suppress Aeromonas spp.

Keywords: Aeromonas spp.; enzyme-based test; E. coli; groundwater; total coliform