Q.70 The most common indicator organism of faecal pollution in water is
(A) Clostridium botulinum (B) Bacillus subtilis (C) Escherichia coli (D) Clostridium tetani
Escherichia coli (E. coli) serves as the standard indicator organism for faecal pollution in water due to its presence in human and animal intestines.
The correct answer is (C).
Indicator Organism Role
E. coli is a coliform bacterium found exclusively in warm-blooded animal faeces at high concentrations (10^6-10^9/g). Its detection in water signals recent faecal contamination and potential pathogens (Salmonella, Vibrio, viruses), without needing to culture all hazards. It survives similarly to enteric pathogens but doesn’t multiply significantly in water.
Option Breakdown
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(A) Clostridium botulinum: Wrong—anaerobic spore-former causing botulism via neurotoxins in anaerobic canned foods, not faecal indicator or water pollution marker.
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(B) Bacillus subtilis: Wrong—ubiquitous soil saprophyte used in labs (e.g., transformation), survives anywhere but not gut-specific or faecal correlate.
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(C) Escherichia coli: Correct—WHO/EPA standard; thermotolerant coliforms (44.5°C) confirm faecal origin over environmental coliforms like Klebsiella.
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(D) Clostridium tetani: Wrong—soil anaerobe causing tetanus via wounds, not waterborne or reliably faecal-linked.
Introduction to Faecal Pollution Water Indicator Organism
Faecal pollution water indicator organism E. coli detects sewage contamination in drinking/recreational water—crucial GATE Life Sciences microbiology topic. Coliform presence flags pathogens without direct testing; E. coli specificity beats total coliforms.
Why E. coli Excels
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Gut-specific: 10^9 CFU/g faeces, absent in uncontaminated water.
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Survival match: Persists like Salmonella/Shigella but non-pathogenic.
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Detection: MacConkey agar (pink colonies), IMViC++ profile.
Comparison Table
| Organism | Faecal Link? | Water Indicator Role |
|---|---|---|
| E. coli | Yes (universal) | Standard (C) |
| C. botulinum | No (anaerobic toxin) | Food poisoning only |
| B. subtilis | No (soil saprophyte) | Lab tool, environmental |
| C. tetani | No (soil anaerobe) | Wound tetanus |
GATE Exam Tip
Faecal pollution water indicator organism PYQs test public health micro. Remember: E. coli > others for specificity/survival correlation = (C). Master MPN/coliform standards.
