Purpose: This project examined factors that may contribute to the regional contamination of irrigation water by S. enterica and characterized strains isolated from this area.
Methods: S. enterica levels were determined monthly in irrigation water and sediments from a diverse set of farms (n = 10) within the SRW. Various (n = 21) physical/biological parameters were assessed, including fecal indicators. Molecular typing (DiversiLab rep-PCR) was used to determine the relationship of pond isolates (n = 96) to clinical vs. environmental strains (n > 300). Multiplex PCR was performed to predict serotypes (n = 104), and antibiotic resistance of strains (n = 193) was also evaluated.
Results: To date, all 10 ponds were positive for Salmonella from both water and sediment samples. Levels ranged from non-detectable to > 110.0 MPN/100g and frequency from 11.1 to 50%, with some ponds significantly higher than others (P < 0.05). Significant correlations between Salmonella levels and fecal coliforms (r = 0.28, P < 0.01) and E. coli (r = 0.27, P < 0.01) were observed, although correlations for any single parameter were all r < 0.3. Multiplex PCR patterns corresponded to 10 known serotypes, including Newport, but most (81%) showed no identifiable patterns. Pond isolates clustered into 12 genotypes (based on > 85% similarity by rep-PCR), and more strains (50%) were associated with isolates from clinical infections than with strains from the Suwannee River (35%), while some strains (15%) were unique to this study. Antibiotic resistance was observed mostly to streptomycin (100%) and kanamycin (10.4%), with 19.7% resistant to two or more antibiotics.
Significance: These data suggest that these ponds harbor a diverse population of Salmonella, which may pose potential health risks due to their genetic similarity to strains from clinical origin.