This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment, Subject name: Social & Preventive Medicine
Which of the following is a bacteriological indicator of water quality? 
Select and explain. 
A. Staphylococcus aureus, B. Clostridium tetani, C. E.coli, D. Yersinia pestis
C: E.coli
Answer: C: E.coli 
Explanation: Coliform organisms: Primary & most reliable bacterial indicator for water quality. E. coli is most impoant coliform indicator. Fecal streptococci: Indicate 'recent contamination of water'. Clostridium perfringens: Indicate 'remote contamination of water'.