An assessment of Bacteroides fragilis group organisms as indicators of human faecal pollution.

Membrane filtration techniques were used to enumerate Bacteroides fragilis group (BFG) organisms and Escherichia coli in a variety of natural waters, the influents and effluents from three types of sewage treatment plants and faeces of various animals. The results suggest that BFG organisms die off more rapidly than E. coli in water and that animal faeces are not a significant source of BFG. It is suggested that the ratio of BFG to E. coli in water may be used to indicate the proximity of a source of human faecal contamination.