E. coli & coliforms, semiquantitative [ECOLI-S]

Published: July 8th, 2009

Revised: March 21st, 2023

Coliform bacteria are common environmental bacteria, typically associated with the mammalian digestive tract. Although not generally pathogenic themselves, coliforms are a well-known marker of fecal contamination, and their presence is interpreted to suggest that potentially pathogenic bacteria may be present.

This test detects both E. coli and coliform bacteria and is adapted from the Health Canada method used to test recreational water quality. Testing for E. coli and coliform bacteria together increases the analytical specificity of the test, and reduces the potential for false positive results.

This test uses a special growth medium for coliform bacteria that is incubated for a minimum of 48 hr prior to analysis, and enumerates total coliforms, parting out E. coli specifically. The number of colonies per plate or strip is enumerated, and the result is normally expressed semiquantitatively as 1+, 2+. 3+, etc., where the number preceding the “plus sign” indicates the order of magnitude of colonies observed. Please note, we are unable to perform this test for the purpose of assessing drinking water potability. This test is normally conducted using a swab or bulk sample.

Laboratory code: ECOLI-S

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