Microbial quality of agricultural water in Central Florida.

Pina Fratamico,Zeynal Topalcengiz,Michelle D Danyluk,Laura K Strawn

doi:10.1371/journal.pone.0174889

Pina Fratamico, Zeynal Topalcengiz + Show 2 more

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https://doi.org/10.1371/journal.pone.0174889

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Abstract

The microbial quality of water that comes into the edible portion of produce is believed to directly relate to the safety of produce, and metrics describing indicator organisms are commonly used to ensure safety. The US FDA Produce Safety Rule (PSR) sets very specific microbiological water quality metrics for agricultural water that contacts the harvestable portion of produce. Validation of these metrics for agricultural water is essential for produce safety. Water samples (500 mL) from six agricultural ponds were collected during the 2012/2013 and 2013/2014 growing seasons (46 and 44 samples respectively, 540 from all ponds). Microbial indicator populations (total coliforms, generic Escherichia coli, and enterococci) were enumerated, environmental variables (temperature, pH, conductivity, redox potential, and turbidity) measured, and pathogen presence evaluated by PCR. Salmonella isolates were serotyped and analyzed by pulsed-field gel electrophoresis. Following rain events, coliforms increased up to 4.2 log MPN/100 mL. Populations of coliforms and enterococci ranged from 2 to 8 and 1 to 5 log MPN/100 mL, respectively. Microbial indicators did not correlate with environmental variables, except pH (P<0.0001). The invA gene (Salmonella) was detected in 26/540 (4.8%) samples, in all ponds and growing seasons, and 14 serotypes detected. Six STEC genes were detected in samples: hly (83.3%), fliC (51.8%), eaeA (17.4%), rfbE (17.4%), stx-I (32.6%), stx-II (9.4%). While all ponds met the PSR requirements, at least one virulence gene from Salmonella (invA-4.8%) or STEC (stx-I-32.6%, stx-II-9.4%) was detected in each pond. Water quality for tested agricultural ponds, below recommended standards, did not guarantee the absence of pathogens. Investigating the relationships among physicochemical attributes, environmental factors, indicator microorganisms, and pathogen presence allows researchers to have a greater understanding of contamination risks from agricultural surface waters in the field.

Highlights

The United States Congress authorized the Food and Drug Administration (FDA) to set up minimum safety standards for the production and harvest of fruits and vegetables that may be consumed without any further processing [1]
In the proposed Food Safety Modernization Act (FSMA) Produce Safety Rule in 2013, metrics for water quality allowed generic Escherichia coli populations in water that directly contacted the harvestable portion of the crop 235 MPN/100 mL, with a geometric mean (n = 5) 126 MPN/100 mL
The objectives of this study were to i) monitor indicator microbial populations in surface water weekly over the course of two growing seasons; ii) increase monitoring frequency during high water usage or weather events to determine their impact on microbial populations; iii) evaluate the final Produce Safety Rules agricultural water requirements for Central Florida surface water; iv) determine correlation between microbial indicators and physicochemical water attributes; and v) determine correlation of indicator organisms and the presence of Salmonella and shiga-toxin producing E. coli (STEC) genes in the tested water samples

Summary

Introduction

The United States Congress authorized the Food and Drug Administration (FDA) to set up minimum safety standards for the production and harvest of fruits and vegetables that may be consumed without any further processing [1]. Science based standards to minimize the risk of outbreaks related to the consumption of fruit and vegetables have been established in the Food Safety Modernization Act (FSMA) Final Rule on Produce Safety named as “Standards for the Growing, Harvesting, Packing, and Holding of Produce for Human Consumption; Final Rule” [2]. In the proposed FSMA Produce Safety Rule in 2013, metrics for water quality allowed generic Escherichia coli populations in water that directly contacted the harvestable portion of the crop 235 MPN/100 mL, with a geometric mean (n = 5) 126 MPN/100 mL. Water exceeding this number was to be retested, not used, or used by reducing potential contamination risk of produce. A seven-day testing frequency was required for untreated surface water subjected to run off during the growing season [3]

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