Low Concentration of Salmonella enterica and Generic Escherichia coli in Farm Ponds and Irrigation Distribution Systems Used for Mixed Produce Production in Southern Georgia

Abstract

Studies have shown that irrigation water can be a vector for pathogenic bacteria. Due to this, the Food Safety Modernization Act's (FSMA) produce safety rule requires that agricultural water directly applied to produce be safe and of adequate sanitary quality for use, which may pose a challenge for some farmers. The purpose of this research was to assess the presence and concentration of Salmonella and generic Escherichia coli in irrigation water from distribution systems in a mixed produce production region of southern Georgia. Water samples were collected during three growing seasons at three farms irrigating crops with surface water (Pond 1, Pond 2) or groundwater (Well) during 2012-2013. Salmonella and generic E. coli populations were monitored by culture and Most Probable Number (MPN). Confirmed isolates were characterized by pulsed-field gel electrophoresis and serotyping. In Pond 1, Salmonella was detected in 2/21 surface, 5/26 subsurface, 10/50 center pivot, and 0/16 solid set sprinkler head water samples. In Pond 2, Salmonella was detected in 2/18 surface, 1/18 subsurface, 6/36 drip line start, and 8/36 drip line end water samples. Twenty-six well pumps and 64 associated drip line water samples were negative. The overall mean Salmonella concentration for positive water samples was 0.03 MPN/100 mL (range <0.0011-1.8 MPN/100 mL). Nine Salmonella serovars comprising 22 pulsotypes were identified. Identical serovars and subtypes were found three times on the same day and location: Pond 1-Pivot-Cantaloupe (serovar Rubislaw), Pond 1-Pivot-Peanut (serovar Saintpaul), and Pond 2-Drip Line Start-Drip Line End-Yellow Squash (serovar III_16z10:e,n,x,z15). Generic E. coli was detected in water from both farm ponds and irrigation distribution systems, but the concentrations met FSMA microbial water quality criteria. The results from this study will allow producers in southern Georgia to better understand how potential pathogens move through irrigation distribution systems.

Keywords: Escherichia coli; Food Safety Modernization Act (FSMA); Salmonella; irrigation water; on-farm food safety.

FIG. 1.

Map of the Southern Coastal Plain Land Resource Region, United States Department of Agriculture (USDA), Natural Resources Conservation Services (NRCS).

FIG. 2.

A general sampling schematic for a center pivot and drip line irrigation systems fed by a pond. Yellow arrows indicate the location points where water was collected from during this study.

FIG. 3.

Pulsed-field gel electrophoresis analysis following Xba1 digestion of selected Salmonella isolates from farm ponds and distribution systems. ID: laboratory identification code; Date: date when samples were collected; Rotation: crop grown at the time of collection; Source-Sample type: water irrigation source-site along irrigation system where samples were collected; Serovar: Salmonella serovar of isolate; Pulsotype: arbitrarily assigned number of different molecular fingerprints within the comparison, where fingerprints with the same pulsotype were considered indistinguishable.