What is an indicator organism?

An indicator organism is defined as a specific type of organism whose presence in a sample suggests the potential presence of pathogenic organisms, particularly bacteria that can pose health risks. These organisms are commonly used in microbiology and environmental testing to assess water quality because they are typically easier to detect and quantify than the pathogens themselves. For example, coliform bacteria are frequently utilized as indicator organisms since their presence indicates possible contamination by fecal material and, consequently, the likelihood of harmful pathogens being present as well.

In contrast, the other choices refer to unrelated themes. For instance, an organism that indicates neutral pH levels does not serve as an indicator for pathogens or contamination. Similarly, an organism suggesting the quality of taste is not relevant to microbiological testing but rather pertains to sensory evaluations. Lastly, a type of algae used in testing does not fit the definition of an indicator organism, as it does not specifically indicate the presence of pathogens. Therefore, the correct answer is the one that aligns with the primary role of indicator organisms in assessing microbial water quality.