The presence of which of the following is most easily identified by laboratory analysis in water contaminated by feces?

The identification of coliform bacteria in water contaminated by feces is a well-established method for assessing water quality, particularly in relation to fecal contamination. Coliforms, which include a broad group of bacteria (such as Escherichia coli), serve as indicators of microbial contamination due to their frequent presence in the intestines of warm-blooded animals.

Laboratory analysis for coliforms is straightforward and established in water testing protocols, making them the most easily identifiable indicators of fecal contamination. Testing methods are designed to detect coliforms, typically using techniques such as membrane filtration or most probable number (MPN) analysis, which are routinely employed in environmental and public health laboratories. These methods can yield results relatively quickly and are sensitive enough to detect low levels of contamination.

In contrast, while organisms like Shigella dysenteriae, Entamoeba histolytica, and Salmonella typhosa can also indicate fecal contamination, their detection often requires more specialized and time-consuming laboratory methods. These pathogens may not be present in as high numbers as coliforms in fecal matter, complicating their identification and making coliforms the preferable choice for initial contamination screening in water quality assessments.