What differentiates coliforms from E. coli in water testing?

The distinguishing factor between coliforms and E. coli in water testing lies in their implications regarding fecal contamination. Coliforms serve as a general indicator of fecal contamination, suggesting that there may be bacteria present that could originate from the intestinal tract of warm-blooded animals. They do not specify the source of contamination but indicate that there is potential for pathogens to be present.

On the other hand, E. coli is a specific type of coliform bacterium that is predominantly found in the intestines of humans and animals. Its presence in water samples is a strong indicator of fecal contamination originating from warm-blooded animals, thus serving as a more precise marker for the risk of pathogens. In other words, while all E. coli are technically coliforms, not all coliforms are E. coli.

The other choices do not accurately capture the relationship between coliforms and E. coli. For instance, while some coliforms can be less harmful than E. coli, this statement oversimplifies the spectrum of risks associated with different bacterial types. Additionally, the assertion that coliforms are found only in freshwater is incorrect, as coliforms can exist in various environments, including marine and brackish waters.