3. Which one of the following organisms in an indicator of fecal contamination”
(a) Escherichia coli (b) Streptococcs lactic
(c) Bacillus subtilis (d) Lactobacillus acidophilus
Escherichia coli serves as the standard indicator organism for fecal contamination in water, making it the correct choice in this multiple-choice question. This article breaks down the options with scientific reasoning for clarity.
Correct Answer
The right answer is (a) Escherichia coli. E. coli resides primarily in the intestines of humans and warm-blooded animals, so its detection in water signals recent fecal pollution and potential pathogens.
Why E. coli?
Regulatory bodies like the U.S. EPA endorse E. coli over total coliforms for monitoring recreational and drinking water due to its specificity to fecal sources. Unlike environmental bacteria, E. coli does not survive long outside hosts, providing a reliable proxy for health risks like gastrointestinal illness.
Option Analysis
| Option | Organism | Role & Why Not an Indicator |
|---|---|---|
| (a) | Escherichia coli | Primary fecal indicator; abundant in intestines, easy to culture, correlates with pathogens |
| (b) | Streptococcus lactic (likely Streptococcus lactis) | Lactic acid bacterium used in dairy fermentation; not fecal-specific, found in milk and plants |
| (c) | Bacillus subtilis | Soil spore-former; indicates general contamination or sterilization efficacy, not feces |
| (d) | Lactobacillus acidophilus | Probiotic in gut flora and yogurt; environmental survival unrelated to fecal pollution |
