The coliform group sensitivity as indicator of the enteropathogenic bacteria presence in four water bodies from Mexico

Abstract

Microbiological pollution in water bodies is characterized through the detection of indicator organisms like total coliform (TC) and fecal coliform (FC) bacteria. The objective of the present paper was to determine the sensibility of these indicators of the presence of pathogenic enterobacteria in four Mexican aquatic systems. Two with major anthropogenic influence: Patzcuaro Lake and Xochimilco Lake ecosystem; and two with less: Metztitlan Lagoon and Zirahuen Lake. TC and FC were quantified with the Most Probable Number technique in water and sediment and enteric bacteria were isolated in water using selective culture media. The sensibility index, the risk attributable, and the presenceabsence of indicators and pathogens were evaluated. Patzcuaro and Xochimilco showed high bacterial pollution. The sediment presented higher concentrations of total and fecal coliforms than water. FC were the most reliable indicators to predict the presence of Salmonella and Shigella, with a sensitivity of 60 and 75%, an attributable risk of 58 and 67% for each genus. FC showed a presence-absence relationship with a percentage of true cases of 82 to 88%. In contrast, TC showed a low attributable risk, inferior to 27% and a high percentage of false positives (65%), which impede to consider it a good indicator. It is convenient to evaluate the presence of indicators and pathogens simultaneously to determine the sanitary risk when characterizing microbial water quality in aquatic ecosystems.