Indication of Fecal contamination of water is due to presence of-
Fecal contamination in water is usually indicated by the presence of certain bacteria. The most common ones are coliforms, specifically Escherichia coli (E. coli). E. coli is a key indicator because it's found in the intestines of warm-blooded animals, so its presence suggests fecal matter is present. Other coliform bacteria might be present in the environment, but E. coli is more specific to fecal contamination.
Wait, but sometimes the question might refer to total coliforms as a group. However, in many cases, especially in exams, E. coli is the correct answer because it's a fecal coliform. So if the options include E. coli, that's the right choice. If the options are between E. coli and other coliforms like Klebsiella or Enterobacter, E. coli is the specific indicator.
The user might have intended options like E. coli, Salmonella, Shigella, or other bacteria. But the standard indicator is E. coli. So the correct answer would be E. coli. Let me structure the explanation accordingly, even without the options. I need to make sure that the core concept is about using E. coli as an indicator, explain why it's the right answer, address possible distractors like other coliforms or pathogens, and give a clinical pearl about water testing standards.
**Core Concept**
Fecal contamination of water is indicated by the presence of **Escherichia coli (E. coli)**, a fecal coliform. This organism is a reliable marker because it is abundant in the intestinal tract of humans and animals but does not persist in the environment independently, unlike other coliforms. Its detection confirms recent fecal pollution and potential pathogen presence.
**Why the Correct Answer is Right**
E. coli is a thermotolerant fecal coliform that thrives in the intestines of warm-blooded organisms. Its presence in water directly correlates with fecal contamination, as it is not naturally found in soil or water. Unlike other coliforms (e.g., Klebsiella), E. coli is a specific indicator of human/animal waste, making it critical for public health assessments. Testing for E. coli (via membrane filtration or PCR) is standard in water quality monitoring.
**Why Each Wrong Option is Incorrect**
**Option A:** *Salmonella typhi* is a pathogen causing typhoid fever but is not routinely used as a fecal indicator due to its low prevalence and slow growth in water.
**Option B:** *Shigella* species cause dysentery but are rare in water and not practical for routine testing.
**Option C:** *Enterobacter* is a non-fecal coliform; its presence may indicate environmental contamination (e.g., soil) rather than fecal matter.
**Clinical Pearl / High-Yield Fact**
**E. coli detection >1 colony/100 mL in water is unsafe for drinking** (WHO guidelines). Remember: "Coliforms may hint, but E. coli confirms" – use E.