Impact of urban contamination of the La Paz River basin on thermotolerant coliform density and occurrence of multiple antibiotic resistant enteric pathogens in river water, irrigated soil and fresh vegetables.

Violeta Poma,Volga Iñiguez,Nataniel Mamani

doi:10.1186/s40064-016-2132-6

Abstract

La Paz River in Andean highlands is heavily polluted with urban run-off and further contaminates agricultural lowlands and downstream waters at the Amazon watershed. Agricultural produce at this region is the main source of vegetables for the major Andean cities of La Paz and El Alto. We conducted a 1 year study, to evaluate microbial quality parameters and occurrence of multiple enteropathogenic bacteria (Enterohemorrhagic E. coli—EHEC, Enteroinvasive E. coli or Shigella—EIEC/Shigella, Enteroaggregative E. coli—EAEC, Enteropathogenic E. coli—EPEC Enterotoxigenic E. coli—ETEC and Salmonella) and its resistance to 11 antibiotics. Four sampling locations were selected: a fresh mountain water reservoir (un-impacted, site 1) and downstream sites receiving wastewater discharges (impacted, sites 2–4). River water (sites 1–4, N = 48), and soil and vegetable samples (site 3, N = 24) were collected during dry (April–September) and rainy seasons (October–March). Throughout the study, thermotolerant coliform density values at impacted sites greatly exceeded the guidelines for recreational and agricultural water uses. Seasonal differences were found for thermotolerant coliform density during dry season in water samples nearby a populated and hospital compound area. In contrast to the un-impacted site, where none of the tested enteropathogens were found, 100 % of surface water, 83 % of soil and 67 % of vegetable samples at impacted sites, were contaminated with at least one enteropathogen, being ETEC and Salmonella the most frequently found. ETEC isolates displayed different patterns of toxin genes among sites. The occurrence of enteropathogens was associated with the thermotolerant coliform density. At impacted sites, multiple enteropathogens were frequently found during rainy season. Among isolated enteropathogens, 50 % were resistant to at least two antibiotics, with resistance to ampicillin, nalidixic acid, trimethoprim–sulfamethoxazole and tetracycline commonly present. Moreover, some Salmonella isolates were distinguished by their multi-resistance to ≥8 antibiotics, within soil and vegetable samples. Overall, this study demonstrates that La Paz River—an affluent of the Amazon macrobasin—is heavily polluted along the year with a high density of thermotolerant coliforms and is a reservoir of multiple antibiotic resistant enteropathogens, present in river water, soil and vegetables. These data highlight health risk associated with food and waterborne diseases at the region.

Highlights

Worldwide, the contamination of fresh water resources due to urbanization affects food security and ecosystem sustainability (WWAP 2012)
This is the case of the agricultural production along La Paz River basin, where river effluents are highly valued by farmers, allowing for a continuous crop production throughout the year, to respond to the growing food demand of the nearby cities of La Paz and El Alto, which are the biggest urban centers in the Bolivian Andean highlands (MMAyA 2012)
Mean values of multiple antibiotic resistance (MAR) Index were calculated for each type of sample and across all samples the density of thermotolerant coliforms found in fresh produce exceeded the satisfactory microbiological hygiene criteria level 1000 MPN/100 g of fresh weight (ICMSF 1996)

Summary

Introduction

The contamination of fresh water resources due to urbanization affects food security and ecosystem sustainability (WWAP 2012) This situation is exacerbated in developing countries and more so in dry regions such as the Bolivian Highlands, where population growth, urban expansion and widespread malnutrition give rise to an increasing demand for water that is crucial for food security (Buxton et al 2013). In this region, along with a shortage of water, urban wastewater directly drains into fresh water bodies that flow downstream into the Amazon macrobasin, contributing to its aquatic ecosystem degradation. This situation may likely be exacerbated by climate change in the coming years, increasing human exposure to environmental pathogens (Boxall et al 2009)

Objectives

Methods

Results

Discussion

Conclusion