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

The objective of the present paper was to determine the sensibility of indicator organisms for detecting he 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. Total coliform (TC) and fecal coliform (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 presence/absence 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, less than 27% and a high percentage of false positives (65%), which does not allow 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.Original Abstract: El objetivo de este trabajo fue determinar la sensibilidad de estos indicadores para predecir la presencia de enterobacterias patogenas en cuatro cuerpos acuaticos mexicanos. Dos con mayor influencia humana: lago de Patzcuaro, Mich. y ecosistema lacustre de Xochimilco, D. F y dos con menor: la laguna de Metztitlan, Hgo. y el lago Zirahuen, Mich. Se cuantificaron coliformes totales y coliformes fecales en agua y sedimento por la tecnica del Numero Mas Probable y se aislaron bacterias entericas del agua mediante el uso de medios de cultivo selectivos. Se evaluaron: el indice de sensibilidad, el riesgo atribuible y la presenciaausencia de indicadores y patogenos. Patzcuaro y Xochimilco mostraron alta contaminacion bacteriana. El sedimento presento mayor concentracion de CT y CF que el agua. Los CF mostraron ser indicadores mas confiables para predecir la presencia de Salmonella y Shigella, con una sensibilidad para cada genero de 60 y 75% y un riesgo atribuible del 58 y 67%. Los CF mostraron una relacion presencia-ausencia con un porcentaje de casos verdaderos del 82 a 88%. En contr