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The objective of this study was to evaluate the influencing factors in the occurrence of coliforms in the drinking water in La Plata (Argentina) from June 1999 to June 2001. A total of 180 samples were collected from Rio de La Plata (102 samples) and Puelche Aquifer (78 samples); 45 samples were collected for each of the four seasons. The membrane filter procedure was used for isolating bacteria, and each sample was tested for chlorine and pH. The highest percentage of samples positive for coliforms in the two tested media was obtained in summer while the highest percentage of negative samples was obtained in winter. No Escherichia coli was isolated. The percentage of injured coliforms fluctuated between 70 and 100%. The most frequently isolated bacteria was Enterobacter cloacae in summer, Enterobacter agglomerans in autumn and Klebsiella oxytoca in winter and spring. Significant correlations were observed between coliforms and the distance from the initial treatment point, and with the level of free chlorine. We conclude that drinking water contamination in La Plata occurs in the distribution system due to increased temperatures and reduced disinfectant levels, which result in bacterial regrowth.

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Cryptosporidium es un parásito causante de cryptosporidiosis. Su estadío infectivo, el ooquiste, se elimina con las heces del hospedador, representando los terneros la principal fuente de infección humana. El objetivo de este trabajo fue comparar tres métodos de concentración de heces para recuperar ooquistes de Cryptosporidium. Fueron estudiados un total de 166 terneros. Una única muestra de materia fecal fresca fue analizada por los métodos de Telemann modificado, agua éter, y Tris Tween 80. La identificación de ooquistes fue realizada mediante coloración de Kinyoun modificada. El número de ooquistes concentrados por cada técnica fue cuantificado en 20 campos a 1000X. Del total de muestras analizadas, 22/166 fueron positivas para Cryptosporidium. El número medio de ooquistes recuperados por cada técnica fue: Telemann modificada (124,2±159,5), agua éter (153,0±156,3), tris Tween 80 (92,2±98,3). ANOVA mostró que no existen diferencias significativas entre métodos. De acuerdo con los resultados obtenidos, las tres técnicas pueden ser empleadas para concentrar ooquistes de Cryptosporidium. Si bien los tres métodos presentaron igual sensibilidad y espcificidad, la técnica de agua éter demostró ser sencilla, de bajo costo, y efectiva para recuperar ooquistes, particularmente si se requiere conservar la viabilidad de los mismos.

Cryptosporidium is a parasite which causes cryptosporidiosis. Its infectious stage, the oocyst, is eliminated with the host feces, calves being the main source of human infection. The aim of the present work was to compare three methods of feces concentration to recover Cryptosporidium oocysts. A total of 166 calves were studied. An only sample of fresh feces was analyzed using the following methods: modified Telemann, water ether, and Tris Tween 80. The identification of oocysts was carried out by modified staining Kinyoun technique. The number of concentrated oocysts per technique was quantified in 20 fields at 1000X. From a total of 166 analyzed samples, 22 were Cryptosporidium positive. The average number of recovered oocysts per technique was: modified Telemann (124.2±159.5), water ether (153.0±156.3), Tris Tween 80 (92.2 ± 98.3). ANOVA demonstrated that there are no significant differences between these methods. According to the results obtained, the three techniques may be used to concentrate Cryptosporidium oocysts. Even if there are no differences in sensibility and specificity between these methods, the water ether technique proved to be simple, low-cost, and effective to recover oocysts, particularly if the oocysts condition is to be kept.

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