The major bacteriological indicator of fecal contamination of drinking water is:

Correct option is C

Coliform count (esp. E. coli) is the standard indicator of fecal contamination, used in water quality testing.
Explanation of options: (a) ✘ Typhoid bacilli are pathogens, not routine indicators. (b) ✘ V. cholerae causes outbreaks, not a standard indicator. (c) ✔ Correct; coliforms are most reliable fecal contamination markers. (d) ✘ Clostridia indicate past contamination, not routine test.