In addition to viruses, bacteria (microscopic organisms that can reproduce without a host in the proper conditions) are also found in water. In general, damage to the human body from bacterial infection is due to the action of the toxins they produce. Bacteria found in water are derived from contact with air, soil, living and decaying plants and animals, and animal excrements. Many of these bacteria are aerobic and anaerobic spore-forming organisms associated with varying densities of coliforms, fecal coliforms, fecal streptococci, staphylococci, chromogenic forms, fluorescent strains, nitrifying and denitrifying groups, iron and sulfur bacteria, proteus species, and pathogenic bacteria. Many bacteria are of little sanitary significance and die rapidly in water. Fecal pollution adds a variety of intestinal pathogens. The most common genera found in water are salmonella, shigella, vibrio, mycobacterium, pasteurella, and leptospira.
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