This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Preferred bacteriological indicator of faecal contamination of water: March 2012 
Select and explain. 
A. Faecal streptococci, B. Cl. prefringens, C. Faecal staphylococci, D. E.coli
D: E.coli
Answer: D: E.coli 
Explanation: Ans: D i.e. E. coli The primary bacterial indicator recommended for acceptability purpose is the coliform group of organisms as a whole. The coliform group includes both faecal (E.coli) and non faecal organisms (Klebsiella aerogens) Supplementary indicator organisms, such as faecal streptococci and sulphite-reducing clostridia, may sometimes be useful in determining the origin of faecal pollution as well as in assessing the efficiency of water treatment processes.