The presence of _________in a water sample usually means pathogens have contaminated the source.

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Understand that the question is asking about an indicator organism or substance whose presence in water suggests contamination by pathogens.

Recall that in microbiology, certain bacteria are used as indicators of fecal contamination because they are commonly found in the intestines of warm-blooded animals and their presence suggests possible contamination by harmful microorganisms.

Identify that coliform bacteria, especially Escherichia coli (E. coli), are widely used as indicator organisms in water quality testing.

Recognize that the presence of coliform bacteria in a water sample usually means that pathogens have contaminated the source, as these bacteria indicate fecal contamination.

Therefore, the blank in the sentence should be filled with 'coliform bacteria' or simply 'coliforms' to correctly complete the statement.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Indicator Organisms

Indicator organisms are microbes used to detect contamination in water, signaling the possible presence of pathogens. They are typically harmless bacteria whose presence suggests fecal contamination, making them useful for water quality testing.

Fecal Contamination

Fecal contamination occurs when water is polluted with feces from humans or animals, introducing harmful microorganisms. This contamination is a major source of waterborne diseases and is often indicated by specific bacteria like coliforms.

Coliform Bacteria

Coliform bacteria are a group of rod-shaped bacteria commonly found in the intestines of warm-blooded animals. Their presence in water samples is a standard indicator of fecal contamination and potential pathogen presence.

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