Volume 57, Issue 4
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Diarrheal diseases often result from ingestion of contaminated water or food. The population of La Paz, Bolivia is directly or indirectly exposed to the sewage-contaminated La Paz River. We conducted a bacteriologic survey of the La Paz River to quantify the level of bacterial contamination, with particular reference to enteropathogens. A total bacterial count exceeding 10 colony-forming units (CFU)/ml, including lactose fermenting and non-fermenting, gram-negative bacilli of approximately 10 CFU/ml, respectively, were detected in river water samples collected near two densely populated areas. A total bacterial count of 10 CFU/ml was also detected at the most downstream area of the river near a sparsely populated area. At four sampling locations, several enteropathogens were detected, including five enterotoxigenic (ETEC) (serotype O6, O15, and O159), two enteropathogenic (EPEC) (serotype O44), two enteroinvasive (EIEC) (serotype 029), and three O4 group isolates. The heat-labile enterotoxin gene and the invasive toxin gene were detected in all ETEC and EIEC isolates by polymerase chain reaction analysis. Nine isolates of were found by the agar dilution method to be susceptible to ampicillin, kanamycin, nalidixic acid, tetracycline, and chloramphenicol, and ampicillin resistance was found in only two isolates of EIEC 7-4 (serotype O29) and EPEC 7-5 (serotype O44). Ampicillin resistance was coded on plasmids and transferred conjugatively to χ1037 at a frequency of 10- CFU/donor by the broth mating method. Strains of , which can cause diarrheal disease in infants, were detected in vegetables grown in fields irrigated by water from the La Paz River. The survival of nine isolates of in filtered river water was compared with that of laboratory strains ( χ1037, W3110, and ATCC29577). The survival time of seven isolates, excluding two ampicillin-resistant isolates, was markedly longer than that of the laboratory strains. Our results show a high bacterial contamination of the La Paz river and suggest that such levels may contribute to the high incidence of diarrheal disease in the city of La Paz.


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