Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Which one of the following organisms is an indicator of fecal contamination?
Options:
(A) Escherichia coli
(B) Streptococcus lactis
(C) Bacillus subtilis
(D) Lactobacillus acidophilus
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2017 Q.03)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Microbiology & Environmental Biotechnology (Water Quality & Coliform Indicators)
**2. Detailed Step-by-Step Analysis**:
- In environmental and public health microbiology, testing water supplies directly for scarce, diverse enteric pathogens (such as *Salmonella*, *Shigella*, Vibrio, or hepatitis viruses) is impractical.
- Instead, regulatory standards employ **fecal indicator bacteria (FIB)**:
- An ideal indicator bacterium must be an abundant normal inhabitant of the gastrointestinal tract of warm-blooded animals, be present in large numbers when feces are present, survive similarly to pathogens in water, and be easily detected by simple microbiological assays.
- **Escherichia coli** (a Gram-negative, rod-shaped, facultative anaerobic coliform) is universally utilized as the benchmark indicator of recent fecal contamination in potable water, recreational waters, and food products.
- **Option-by-Option Evaluation**:
- **Option (A) [CORRECT]**: *Escherichia coli* is the universally established indicator organism for fecal contamination.
- **Option (B) [INCORRECT]**: *Streptococcus lactis* (*Lactococcus lactis*) is a non-pathogenic lactic acid bacterium used in dairy and cheese starter cultures.
- **Option (C) [INCORRECT]**: *Bacillus subtilis* is a ubiquitous, spore-forming soil saprophyte, not an indicator of fecal pollution.
- **Option (D) [INCORRECT]**: *Lactobacillus acidophilus* is a probiotic found in fermented dairy foods and normal vaginal flora, not an environmental fecal indicator.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **A**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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