# Large-volume sampling for improved characterization of microbial contamination in agricultural waters: a case study from southeastern U.S. produce farms

## TL;DR

This study shows that large-volume water sampling improves detection of harmful microbes and contamination sources in agricultural irrigation water.

## Contribution

The study introduces and validates large-volume sampling using DEUF for more sensitive detection of pathogens and fecal indicators in agricultural waters.

## Key findings

- DEUF sampling detected higher rates of Salmonella and fecal indicators compared to traditional grab sampling.
- DEUF revealed associations between Salmonella and fecal indicators that were not detected using grab sampling.
- DEUF is effective for detecting pathogens, fecal indicators, and MST markers in agricultural irrigation water.

## Abstract

Fresh produce growers in the United States are required to conduct agricultural water assessments to help mitigate the risks associated with potentially contaminated irrigation water. Microbial water quality is typically assessed using the fecal indicator bacteria, Escherichia coli, collected from small-volume grab samples. Testing irrigation water for alternative fecal indicators, microbial source tracking (MST) markers, or pathogens may provide additional insight into sources of fecal contamination, risk of pathogen presence, or hazards associated with the agricultural watershed. In this study, we conducted laboratory recovery experiments and a field study to evaluate sample collection methods for agricultural water assessments. Dead-end ultrafiltration (DEUF) was used to collect large-volume (50 L) irrigation water samples alongside 1-L grab samples monthly from three farms in southern Georgia, USA, for 1 year. DEUF and grab samples were analyzed for fecal indicators, Salmonella, E. coli O157:H7, and MST markers. DEUF resulted in higher detection rates than grab sampling for Salmonella and most fecal indicators. DEUF also revealed associations between Salmonella and fecal indicators that grab sampling did not. This study demonstrates the applicability and benefit of DEUF for the sensitive detection of pathogens, fecal indicators, and MST markers in produce irrigation water.