Discussion
Which indicator bacteria indicates recent fecal contamination of water and detected in glucose azide broth ?
Answer: B
The indicator is Streptococcus faecalis.
Faecal streptococci (now Enterococcus faecalis and relatives) live in the intestines of humans and warm-blooded animals and do not multiply in water, so their presence points to recent faecal contamination. They are detected in glucose (dextrose) azide broth: sodium azide suppresses gram-negative bacteria, while the streptococci grow and produce acid from glucose.
E. coli is also a faecal indicator, but it is gram-negative and so inhibited by azide. Clostridium perfringens forms spores that persist for long periods and indicates remote rather than recent pollution. Listeria monocytogenes is a pathogen, not a faecal indicator.
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