Purpose: To investigate the role of irrigation waters as potential sources of produce contamination by foodborne pathogens.
Methods: Fifteen samples were collected from irrigation canals in Yuma and Maricopa Counties in Arizona, for four months during the leafy greens growing (December-March) and non-growing (July-October) seasons over two years (236 total); 1-l grab samples were collected for bacteria and 100-l samples using NanoCeram® filters for viruses. Filter eluates were further concentrated using centrifugal ultrafiltration. HAV, NoV, Aichiviruses (AiV), and pepper mild mottle virus (PMMV) were identified using qPCR.
Results: All samples were negative for NoV, HAV, and AiV; however, 28.6% of samples had PMMV present. A majority of samples tested positive by Colilert® for coliforms (100%) and E. coli (88.1%). None of the sites exceeded current standards of 126 E. coli/100ml (geometric mean; ≥5 samples). Salmonella (14.0% water, 22.6% sediment samples) and/or E. coli (9.3% water, 8.1% sediment samples) were isolated using enrichment/selection methods. Salmonella were confirmed via PCR for invA and himA genes; no E. coli were positive for O157 antigen or virulence genes (stx1/stx2/eae). No overall correlations were found between any water quality parameters collected, the presence of bacteria, and the presence of PMMV. The average numbers of PMMV per site in Yuma (but not Maricopa) could be weakly correlated with the occurrence of coliforms (r = 0.69), E. coli in water (r = 0.72 and r = 0.57 for Colilert® and enrichment/selection, respectively), and Salmonella in water (r = 0.51).
Significance: Although no pathogenic viruses were found, the presence of PMMV suggests human fecal contamination. Also, although it appears that these irrigation waters are generally of high quality, pathogens are present on occasion. Thus, the water may be a potential source of crop contamination.