Which of the following is an example of disease-causing organisms that can enter water when human sewage contaminates it?

• A. Algae
• B. Nitrifying bacteria
• C. Yeast
• D. Fecal coliform bacteria

Answer: (D)

Sewage contamination introduces microorganisms from human waste into water, creating a risk of disease. Fecal coliform bacteria come directly from feces and are used as indicators of fecal contamination in water. Their presence signals that sewage-derived pathogens—such as certain bacteria, viruses, or protozoa—could also be present, so they are a key example of disease-related organisms entering water through sewage. The other options don’t reflect organisms tied to sewage-driven disease risk: algae are photosynthetic and can bloom in polluted water, nitrifying bacteria are part of the nitrogen cycle, and yeast are fungi not specifically linked to sewage-borne disease in this context.