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Environmental Analysis

Total & thermotolerant coliforms [FECAL]

Published: July 8th, 2009

Revised: January 23rd, 2019

Coliform bacteria are common environmental bacteria, typically associated with the mammalian digestive tract. Thermotolerant (“fecal”) coliforms are a subset of coliform bacteria that survive at 42 °C. Although not generally pathogenic themselves, thermotolerant 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 uses a standard method for detecting both total and thermotolerant coliform bacteria, based on the methods used widely for the analysis of drinking water. Testing for total and thermotolerant coliform bacteria together increases the analytical specificity of the test, and reduces the potential for false positive results.

This test requires two air sample to be collected tandemly on a special growth medium, MacConkey agar with crystal violet. Following collection, one sample is incubated at 35 °C to test for total coliforms, and the partner sample is incubated at 42 °C to determine the presence of thermotolerant coliforms. Coliform bacteria produce distinctive pink colonies that can be further confirmed by other tests. The number of colonies per plate or strip is enumerated, and the result is expressed semiquantitatively as 1+, 2+. 3+, etc., where the number preceding the “plus sign” indicates the order of magnitude of colonies observed.

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