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

Introduction: Because irrigation water has been shown to be a vector for the contamination of fresh produce by pathogenic bacteria, the proposed produce safety rule under the Food Safety Modernization Act (FSMA) requires that agricultural water must be safe and of adequate sanitary quality for its intended use. These requirements may be challenging for farmers using surface water sources such as constructed farm ponds.

Purpose: The purpose of this study was to assess the presence and concentration of Salmonella and indicator bacteria in irrigation water exiting different distribution systems on a mixed produce farm growing tomatoes, squash, peppers, eggplant, cantaloupe, and leafy greens in southern Georgia. 

Methods: Salmonella and generic Escherichia coli concentrations (CFU/100 ml) were monitored in 2 irrigation ponds supplying drip, center pivot, and solid set sprinkler systems and one deep groundwater well feeding a drip system. Samples were collected during three growing seasons in 2012-2013. Salmonella isolates were subtyped by pulsed-field gel electrophoresis (PFGE).

Results: Salmonella was found in water from 15/74 (20%) pond, 12/49 (24%) pivot, 1/24 (4%) solid set sprinkler, 7/48 (15%) drip line (start) and 11/48 (23%) drip line (end) samples. The mean Salmonella concentration was 0.3 MPN/100 ml (range 0.1 – 1.8 MPN/100 ml) in positive samples. No Salmonella or generic E. coli were detected in samples collected from the well (n = 80) or drip system (n = 24) fed from the well. E. coli concentrations in samples from irrigation systems containing Salmonella were below the proposed FSMA threshold of 235 CFU/ 100 ml. Indistinguishable Salmonella subtypes were found in pond-pivot and pond-drip samples collected on the same day and location.

Significance: Knowledge resulting from this project will allow vegetable producers that rely on untreated surface sources of irrigation water to effectively address new rules the FDA may implement on safe agricultural water.