**Question:** The following organism because of its easy culture methods is widely used as bacteriology indicator of water pollution:

A. Escherichia coli (E. coli)
B. Salmonella typhi
C. Bacillus anthracis
D. Pseudomonas aeruginosa

**Core Concept:** The selection of an organism for water pollution indicator depends on its ease of cultivation in laboratory settings. Indicator organisms are used to assess the overall quality of water samples based on the presence or absence of pathogenic microorganisms.

**Why the Correct Answer is Right:** Escherichia coli (E. coli) is widely used as a bacteriology indicator of water pollution due to its ease of cultivation. E. coli is a member of the Enterobacteriaceae family and is commonly found in the gastrointestinal tract of humans and animals. Many E. coli strains are facultatively anaerobic, enabling growth in laboratory conditions. Furthermore, E. coli can be easily distinguished from other bacteria by colony morphology, biochemical tests, and serotyping.

**Why Each Wrong Option is Incorrect:**

B. Salmonella typhi (S. typhi) is an enteric bacterium causing typhoid fever and is not commonly used as a water pollution indicator due to its pathogenic nature. The focus is on using non-pathogenic organisms for assessing water quality.

C. Bacillus anthracis is the causative agent of anthrax and is not used as a water pollution indicator due to its pathogenicity. Non-pathogenic organisms are preferred for this purpose.

D. Pseudomonas aeruginosa is a versatile aerobic bacterium, not commonly used as a water pollution indicator. Like S. typhi, P. aeruginosa is pathogenic, limiting its suitability for assessing water quality.

**Clinical Pearl:** In selecting an organism as a water pollution indicator, non-pathogenic bacteria that can tolerate and grow under various environmental conditions are preferred. E. coli is a suitable choice due to its facultative anaerobic nature and ease of identification through various laboratory tests. This ensures accurate assessment of water quality and helps prevent the contamination of drinking water sources with potential pathogenic microorganisms.