Faecal Indicator Bacteria

Faecal indicator bacteria are organisms used to signal faecal contamination and the likely presence of waterborne pathogens, since the pathogens themselves are hard to measure routinely. Escherichia coli and intestinal enterococci are the standard indicators for recreational and shellfish waters; total and faecal coliforms are older measures still used in some standards. The EU Bathing Water Directive 2006/7/EC classifies coastal waters as excellent at intestinal enterococci of 100 cfu/100 mL and E. coli of 250 cfu/100 mL on a 95th-percentile basis. Exceedances close beaches and trigger source tracking to sewage outfalls, combined-sewer overflows, and urban runoff. Indicator counts also drive shellfish-harvest area classification.