Indicator organism

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Indicator organisms are used to measure such things as potential fecal contamination of environmental samples. The presence of coliform bacteria, such as E. coli, in surface water is a common indicator of faecal contamination. Coliform bacteria in water samples may be quantified using the most probable number (MPN) method, a probabilistic test which assumes cultivable bacteria meet certain growth and biochemical criteria. If preliminary tests suggest that coliform bacteria are present at numbers in excess of an established cut-off (the Coliform Index), faecal contamination is suspected and confirmatory assays such as the Eijkman test are conducted.[citation needed]

Coliform bacteria selected as indicators of faecal contamination must not persist in the environment for long periods of time following efflux from the intestine, and their presence must be closely correlated with contamination by other faecal organisms. Indicator organisms need not be pathogenic.[1]

Non-coliform bacteria, such as Streptococcus bovis and certain clostridia may also be used as an index of faecal contamination.[2]

See also[edit]


  1. ^ "Fecal Coliform as an Indicator Organism". Wastewater treatment environmental fact sheet. New Hampshire Department of Environmental Services. 2003. Retrieved 2007-11-30. 
  2. ^ Gerardi, Michael H.; Mel C. Zimmerman (January 2005). Michael H. Gerardi, ed. Wastewater Pathogens. Wastewater Microbiology Series. Hoboken, NJ: John Wiley & Sons, Inc. p. 147. ISBN 978-0-471-20692-7.