Detection of coliform bacteria in irrigation water and on vegetable surfaces in the Kathmandu Valley of Nepal

Abstract

Introduction: Consumption of vegetables irrigated using polluted water is widespread in the Kathmandu Valley of Nepal. However, studies on the microbial analysis of water and vegetable samples from this region are limited. In this study, irrigation water and vegetable samples from farmers' fields in the Kathmandu Valley were examined for the presence of Escherichia coli and total coliforms.

Methods: Irrigation water (n = 8) and vegetable (n = 27) samples were collected from November to December 2015. The presence of E. coli and total coliforms in water and on vegetable surfaces was determined by the most probable number (MPN) method using Colilert reagent. In addition, information about vegetable washing and consumption was obtained through a survey to discuss changes in their microbial concentrations before selling and/or consumption.

Results: E. coli was detected in 75% (6/8) of the water samples, with concentrations ranging from 8.8 * 10 ^ 3 to 5.2×107 MPN/100 ml, whereas total coliforms were detected in all the 8 water samples, with concentrations ranging from 9.7 * 10 ^ 2 | 7.9 * 10 ^ 7 * MPN / 100 * m . E. coli was similarly detected in 7% (2/27) of the vegetable samples, with concentrations ranging from 0.4 to 10.2 MPN/cm², whereas total coliforms were detected in 59% (16/27) of the vegetable samples, with concentrations ranging from 0.4 to 448 MPN/cm². Well, river, and tap were the predominant sources of water for washing vegetables before selling and/or consumption.

Conclusions: Unlike water samples, vegetable samples contained low microbial contamination; however, the level of contaminants was expected to increase because of washing with polluted water.