MCQ – 98617

Correct Answer » A Explanation

Clinical Reasoning for the Correct Answer:
– E. coli is the most reliable indicator of recent fecal pollution in water.
– Its presence specifically reflects contamination from the gastrointestinal tract of humans or warm-blooded animals.
– E. coli does not multiply in water environments, so detection suggests direct and recent contamination.

Why Option A (E. coli) is Correct:
– E. coli is a normal inhabitant of the human colon.
– It is not normally present in water unless contaminated by feces.
– Presence in water is used as a “faecal coliform” indicator of recent and potentially dangerous contamination.

Why Option B (Streptococci) is Incorrect:
– Fecal streptococci (e.g., Enterococcus) can indicate fecal contamination, but they may survive longer and can also originate from environmental sources like soil or plants.
– They are less specific than E. coli for recent contamination.

Why Option C (Clostridium) is Incorrect:
– Clostridium perfringens is used as an indicator of remote or intermittent contamination due to its spore-forming nature and persistence in the environment.
– Its presence suggests older or past contamination rather than recent pollution.

Why Option D (Klebsiella) is Incorrect:
– Klebsiella can be present in feces but also occurs in soil, decaying plant material, and water apart from fecal pollution.
– Its occurrence in water does not specifically indicate recent fecal contamination.

High‑Yield Synopsis:

Fecal Indicators in Water Analysis
– Most Specific Indicator:
– Escherichia coli is the gold standard for indicating recent fecal contamination.
– Other Bacterial Indicators:
– Fecal streptococci (Enterococci): less specific; survive longer; some environmental sources.
– Clostridium perfringens: indicates remote contamination (spores persist long-term).
– Klebsiella: not exclusive to fecal origin (also in soil, vegetation).