Environmental Persistence and Naturalization of Fecal Indicator Organisms

Abstract

Fecal indicator bacteria, including total and fecal coliforms, Escherichia coli, and enterococci have been used to indicate the presence of fecal contamination in water used for drinking, shellfishing, and recreation. The assumptions behind the concept of using fecal indicator bacteria (total coliforms, fecal coliforms, E. coli, and enterococci) are that these organisms are normal inhabitants of the gastrointestinal tracts of humans and animals and are incapable of long-term survival or replication outside of their hosts. These assumptions must be valid if FIB levels in water are used to ensure the microbial safety in water and to identify “fecally contaminated” areas, which is essential to microbial source tracking (MST) studies. However, after utilization of total coliforms in the 1920s and fecal coliforms in the 1980s, studies showed that these groups of indicator bacteria failed to meet these assumptions because they include strains that are naturally occurring in nonfecal sources (i.e., soil, vegetation, and water) and are capable of persisting and regrowing in the environment. In the 1980s, E. coli and enterococci were recommended for use as FIB because they were believed to be more specific to fecal waste. Recent studies have shown that these bacteria also failed to meet the criteria for FIB.