| Understanding pathogen prevalence and transmission in agricultural environments is critical to enhance produce safety. An organic farming system (two compost types, irrigation water body, soil and crops) was assessed for presence of E. coli O157 and Salmonella spp. and indicator organism levels (generic E. coli, total and fecal coliforms). Response to heat and starvation was evaluated for ATCC E. coli O157:H7 strains (700599 and 43895) and seven environmental E. coli O157:H7 isolates. Salmonella spp. (24), E. coli O157:H7 (33) and E. coli O157 (two H-, one H+, four H, eight H12 and five H42) were detected in samples collected at various points in the farming system. For both aerated static pile and turned pile compost in at least one year of the study, E. coli O157:H7 was detected after meeting the time and temperature requirements for the process to further reduce pathogens; however pathogens were not detected during field application. Indicator organisms during turned pile composting tended to increase during turning for the first three turns; indicator organism trends for aerated static pile compost varied between years. Pasture plots with no recent soil amendments yielded more E. coli O157 and Salmonella positive soil samples (12/112) compared to vegetable plots where composts were annually applied (6/112). There were no significant (p > 0.05) differences observed in mean indicator organism levels between the pasture and vegetable plots. For irrigation water, sampling date and location significantly influenced indicator organism levels. E. coli O157 and Salmonella were detected in irrigation water samples that met the Washington State Department of Ecology and Leafy Green Marketing Agreement water quality criteria. Type of soil amendment did not affect indicator organism levels on crops, but harvest date within year significantly influenced indicator organism levels on lettuce. E. coli O157 was detected in samples of lettuce and butternut squash in Year 1 when overhead irrigation was used. Environmental E. coli O157:H7 isolates and ATCC strains responded similarly to heat and starvation stress conditions in laboratory experiments. Overall, higher levels of indicator organisms did not accurately reflect the risk of pathogen detection in most agricultural matrices examined. |
