Evaluation of microbial indicators for the determination of bacterial groundwater contamination sources

Several different Microbial source tracking methods (MSTs) can be used to distinguish human from animal fecal contamination in water; In this study, experiments were carried out to test the effectiveness and reliability of three bacteria based approaches (the fecal coliforms to fecal streptococci ratio, antibiotic-resistant Clostridium perfringens, and human bifidobacteria) in a simulated groundwater micro-environment. The methods were evaluated in three phases: initially, the specificity of each indicator was validated on groundwater samples affected by known pollution source; then the variation of performance with time of each method was determined, and finally, the die-off coefficients for pure species of Clostridium perfringens and Bifidobacterium adolescentis were measured. The results indicate that only the determination of human bifidobacteria concentration can be considered reliable in distinguishing human from animal pollution in groundwater at the conditions applied. Nevertheless, human bifidobacteria were detectable only for two weeks after the contamination event. This study also shows that antibiotic resistant Clostridium perfringens detected using the Shahidi-Ferguson medium is not source specific, whereas it confirms that this species can be useful for timing general fecal contamination events.