Anaerobic bacteria as indicators of faecal pollution

Abstract

SynopsisIn several well-authenticated instances intestinal pathogens, includingSalmonellaspecies, have been isolated from water in the absence of bacteria, such asEscherichia coli,commonly used to detect faecal pollution. The present study examines certain anaerobic, non-sporing commensals of the intestinal tract as alternative ‘indicator’ bacteria. The numbers of bifidobacteria andBacteroides fragilisrecovered from faecal specimens were between 109 and 1010 per gram while the Gram-positive, anaerobic cocci numbered only about 106per gram. In sewage, this numerical difference was eliminated by a rapid loss of viability of bifidobacteria andB. fragilisso that the counts of all three types of bacteria approximated to those ofE. coli.Storage tests with aerated and non-aerated sewage established that further loss of viability of bifidobacteria andB. fragilisoccurred only fairly slowly. In samples of water from the Dighty Water and River Tay Estuary, shown to be faecally polluted, the three anaerobic types of bacteria were recovered in numbers roughly equal to those ofE. coliand their persistence in the surface of the bed of the Dighty Water was also at least equal to that ofE. coli.These results demonstrated that, in spite of their strictly anaerobic growth requirements, Bifidobacteria,B. fragilisand the Gram-positive, anaerobic cocci persist in aerobic, aqueous environments. If their habitat can be shown to be reasonably restricted to the intestinal tract they are likely, under special circumstances, to be useful indicators of faecal pollution.