Longitudinal Study of Environmental Factors Influencing Microbial Contamination in Alabama Ponds: Implications for Qualitative Risk Assessment

Abstract

Agricultural water can be a source of microbial contamination for preharvest produce that has been linked to outbreaks and recalls. Over a two-year period, seven agricultural ponds were evaluated bimonthly. A total of 347 samples were tested for EHEC and Salmonella presence using PCR screening. Generic E. coli was quantified and ranged from 1.00 to 4.00 log₁₀ MPN/100 mL. Salmonella was detected in 6% of samples (21/347), and Kentucky was the most frequently isolated serotype. Public health concern serotypes, such as Newport and Hartford, were also isolated. EHEC biomarkers were detected in 83% (289/347) samples, with gene prevalence as follows: hly 68%, fliC 40%, eaeA 19%, rfbE 12%, stx2 10%, and stx1 4%. Microbial water quality and environmental factors were evaluated using conditional forest and regression analyses. Generic E. coli was negatively associated with the amount of developed land within 365 m of the sampling site and dissolved oxygen and positively associated with total rainfall during the 7 days preceding sampling and turbidity. Salmonella detection was positively associated with the amount of pasture within 30 m of the sampling site and total rainfall during the 7 days preceding sampling and negatively associated with rainfall 24 h prior to sampling. EHEC detection was positively associated with percentages of forest and wetland within a 304 m buffer from the sampling site, rainfall 48 h prior to sampling, and solar radiation, while negatively associated with percentages of developed land within a 91 m buffer from the sampling sites. This study provides baseline, longitudinal data on microbial hazards in Alabama agricultural ponds and informs growers on qualitative risk assessment of agricultural waterways.