EN
Bifidobacteria have long since been
recommended as indicators of human and animal
pollution. Concentration ratio (tracking ratio) of
the sorbitol-utilising bifidobacteria (SUB) and the
total bifidobacteria (TB) can be used to distinguish
between animal and human sources of faecal water
contamination. The cut-off value needs to be calibrated
in a given geographical area. Seven sites with permanent
faecal contamination were selected in South Africa.
Concentrations of SUB ranged from 10-50000 cells/100
mL, while TB ranged from 0-8000 cells/100 mL. The
tracking ratio ranged from 0.10 to 6.25, but no clear cut-off
value could be established. The YN-17 agar was replaced
for TB with the modified Beerens medium with pH = 5.70,
to suppress the growth of faecal streptococci. Tracking
ratios observed are most likely the results of different
survival rates of SUB and TB. Bifidobacteria die-off due
to nutrients was not found to be significant using design
of experiment. Thus a lack of continuous input or oxygen
levels in water may be major factors. This would limit the
ratios used as a faecal source tracking method.