Microbial safety considerations of flooding in primary production of leafy greens: A case study |
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| Affiliation: | 1. Food Quality and Design Group, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 17, 6700AA Wageningen, The Netherlands;2. Department of Food Safety and Food Quality, Laboratory of Food Preservation and Food Microbiology, Faculty of Bioscience Engineering, University of Ghent, Coupure Links, 653, 9000 Ghent, Belgium;1. Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, 4200 Highway 97 South, Summerland, BC, Canada V0H 1Z0;2. Department of Food Science and Technology, University of Córdoba, Córdoba, Spain 14014;3. Department of Food Science and Technology, University of California, One Shields Avenue, Davis, CA, USA 95616-8598;4. Western Center for Food Safety, University of California, 1477 Drew Avenue, Davis, CA, USA 95618;5. Canadian Food Inspection Agency, Building 22, 960 Carling Avenue, Ottawa, ON, Canada K1A 0Z2;6. Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, 1391 Sandford Street, London, ON, Canada N5V 4T3;7. Agriculture and Agri-Food Canada, Atlantic Food and Horticulture Research Centre, 32 Main Street, Kentville, NS, Canada B4N 1J5 |
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| Abstract: | This study evaluated the effects of a flood event, floodplain and climatic parameters on microbial contamination of leafy greens grown in the floodplains. Additionally, correlations between pathogenic bacteria and levels of indicator microorganisms have been also determined. To diagnose the microbial contamination after the flood event, sampling was carried out in weeks 1, 3, 5 and 7 after the flooding in four flooded lettuce fields. To assess the impact of flooding on the microbial contamination of leafy greens, indicator microorganisms (coliforms, Escherichia coli and Enterococcus) and pathogenic microorganisms (Salmonella spp., VTEC (E. coli O157:H7 and other verocytotoxin producing E. coli, O26, O103, O111, O145) and Listeria monocytogenes) were evaluated. Irrigation water, soil and lettuce samples showed levels of coliforms and E. coli higher than 5 and 3 log cfu/g or 100 mL, respectively when sampled 1 week after flooding. However, bacterial counts drastically declined three weeks after the flooding. Climatic conditions after flooding, particularly the solar radiation (6–8 MJ/m2), affected the survival of bacteria in the field. L. monocytogenes was not detected in lettuce samples, except for 2 samples collected 3 weeks after the flooding. The presence of Salmonella was detected in irrigation water, soil and lettuce by multiplex PCR one week after the flooding, but only 2 samples of soil and 1 sample of water were confirmed by colony isolation. Verotoxigenic E. coli was detected in soil and lettuce samples by multiplex PCR. Therefore, the implication of flood water as the source of VTEC contamination of soil and lettuce was not clear. E. coli counts in irrigation water were positively correlated with those in lettuce. A significant correlation (P < 0.005) was found between the presence of pathogens and E. coli counts, highlighting a higher probability of detection of pathogens when high levels of E. coli are found. The results obtained in the present study confirm previous knowledge which defined flooding as a main risk factor for the microbial contamination of leafy greens. |
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