Evaluation of Total Coliform, Fecal Coliform, and Fecal Streptococci as Adequate Indicators in Monitoring Public Water Supply Quality in the Tropics

摘要

Previous studies performed in tropical areas demonstrated that high false positive and negative errors were common when determining if fecal contamination of water had occurred; and that pathogens could have a higher survival rate relative to the indicator bacteria. Violations to criteria used to select indicator organisms pose serious doubts about the effectiveness of standard techniques used to assess tropical water quality. The study determines whether Escherichia coli is an adequate indicator of tropical drinking water quality. Water from four treatment plants in Puerto Rico was assayed for the presence of coliforms (total and fecal) and fecal streptococci using membrane filtration and MPN techniques. Ten percent of all fecal coliform positive organisms were isolated and identified. Total bacterial densities were determined by AODC. Results show that although drinking water generally complied with federal regulations, high bacterial densities were still present. Among these, injured (viable but unculturable) coliforms were detected only on m-T7 agar. High levels of false positives are found in all samples. Turbidity affected both disinfection and the normal expression of indicator bacteria on selective media. None of the tested groups seemed to be adequate indicators of tropical water quality.