Abstract
The microbial quality of agricultural water is often assessed using fecal indicator bacteria (FIB) and physicochemical parameters. The presence, direction, and strength of associations between microbial and physicochemical parameters, and the presence of human pathogens in surface water vary across space (e.g., region) and time. This study was undertaken to understand these associations in two produce-growing regions in Florida, USA, and to examine the pathogen ecology in waterways used for produce production. The relationship between Salmonella presence, and microbial and physicochemical water quality; as well as weather and land use factors were evaluated. Water samples were collected from six sites in North Florida (N = 72 samples) and eight sites in South Florida (N = 96 samples) over 12 sampling months. Land use around each sampling site was characterized, and weather and water quality data were collected at each sampling. Salmonella, generic Escherichia coli, total coliform, and aerobic plate count bacteria populations were enumerated in each sample. Univariable and multivariable regression models were then developed to characterize associations between microbial water quality (i.e., E. coli levels and Salmonella presence), and water quality, weather, and land use factors separately for North and South Florida. The E. coli and total coliforms mean concentrations (log10 MPN/100 mL) were 1.8 ± 0.6 and >3.0 ± 0.4 in North and 1.3 ± 0.6 and >3.3 ± 0.2 in South Florida waterways, respectively. While Salmonella was detected in 23.6% (17/72) of North Florida and 28.1% (27/96) of South Florida samples, the concentration ranged between <0.48 and 1.4 log10 MPN/100 mL in North Florida, and <0.48 and 3.0 log10 MPN/100 mL in South Florida. Regression analyses showed no evidence of a correlation between either log10 total coliforms or E. coli levels, and if a sample was Salmonella-positive. The factors associated with Salmonella presence and log10E. coli levels in North Florida differed from those in South Florida; no factors retrained in multivariable regression models were the same for the North and South Florida models. The differences in associations between regions highlight the complexity of understanding pathogen ecology in freshwater environments and suggest substantial differences between intra-state regions in risk factors for Salmonella contamination of agricultural water.
Highlights
Agricultural water used in produce production environments has been identified as a probable route of contamination in past produce outbreaks (Greene et al, 2008; Klontz et al, 2010; Park et al, 2012; Rodrigues et al, 2020)
While under review at the time this manuscript was written (US Food Drug Administration, 2015), the final Produce Safety Rule (PSR) (i) required that agricultural surface water used during produce production establish a microbial water quality profile (MWQP) using 20 samples collected over 2–4 years on a rolling basis, and (ii) that the geometric mean (GM) and statistical threshold value (STV) of E. coli in this sample be ≤126 and ≤410 CFUs/100 mL, respectively
The results presented here support the conclusion from earlier studies that E. coli levels are unreliable as an indicator for the presence and concentration of microbial hazards in agricultural water
Summary
Agricultural water used in produce production environments has been identified as a probable route of contamination in past produce outbreaks (Greene et al, 2008; Klontz et al, 2010; Park et al, 2012; Rodrigues et al, 2020). While under review at the time this manuscript was written (US Food Drug Administration, 2015), the final PSR (i) required that agricultural surface water used during produce production establish a microbial water quality profile (MWQP) using 20 samples collected over 2–4 years on a rolling basis, and (ii) that the geometric mean (GM) and statistical threshold value (STV) of E. coli in this sample be ≤126 and ≤410 CFUs/100 mL, respectively. Water that exceeds these requirements is to be retested, not used, or treated to reduce the potential contamination risk of produce (US Food Drug Administration, 2015). Past studies have shown that meeting the PSR standard may not be indicative of the presence of food safety hazards at the time of water use
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