CALIBRATION OF BIFIDOBACTERIAL INDICATORS FOR MICROBIAL WATER QUALITY MONITORING IN SOUTH AFRICA.

Faecal contamination is of surface water resources is a significant public health problem in South Africa. Once microbial contamination has taken place, its source needs to be identified as soon as possible to decrease public health risks to emergency responders and the population at large. The standard indicator Escherichia coli is currently used as the golden standard in microbial water quality monitoring in South Africa. However, it does not allow for identification of the source of microbial contamination. Concentration ratio of the sorbitol-utilising bifidobacteria and the total bifidobacteria, i.e. tracking ratio, can be used to distinguish between animal and human sources of faecal water contamination based on a cut-off value. The cut-off value to be calibrated for site specific conditions and such a calibration is outline in this paper for South Africa. Seven sites with permanent faecal contamination were selected based on overlap between enumerations of faecal coliforms, E. coli, Rhodococcus coprophilus and the positive hydrogen-sulphide test. Concentrations of faecal coliforms and E. coli ranged from 2 to above 16000 cells/100 cm³. At the same time, concentrations of the sorbitol-utilising bifidobacteria ranged from 10-50000 cells/100 cm³, while the total bifidobacteria concentrations ranged from 0-8000 cells/100 cm³. The tracking ratio ranged from 0.10 to 6.25, but it was not able to distinguish between origins between the human and animal sources of faecal contamination. Results of survival studies showed that the total bifidobacteria died off faster than the sorbitol-utilising ones. Thus total bifidobacteria can be used to detect microbial contamination of surface water up to 48 hours, while finite concentration of sorbitol-utilising bifidobacteria indicates that a longer time has passed since the contamination event. [ABSTRACT FROM AUTHOR]