CORE Organic Project Series Report: PathOrganic Deliverables

Summary in the original language of the document

Consumers are showing an increasing demand for uncooked and minimally processed vegetables preferentially from organic production lines. At the same time, outbreaks of disease have been traced back to the consumption of fresh plant produce contaminated with enteric pathogens such as pathogenic E. coli, Salmonella or Listeria. The PathOrganic project was aimed at assessing risks regarding the infestation of organically produced vegetables with human pathogens. However, the project also analyzed whether organic production may reduce the risk of pathogen manifestation due to improved soil buffering.
Data relating to the current practice in organic vegetable production were assembled by research institutes from six European countries. As the vegetable production systems in the various countries differed considerably, detailed inquiries concerning current management practices and possible sources of contamination of fresh produce on the field were carried out by the use of questionnaires. Our studies showed that the use of untreated animal manure for fertilization constitutes a particular risk regarding contamination of vegetables with human pathogens. Thus, the project was centered on screenings of organic fertilizers as the basis for successive screenings of vegetables grown on farms where a potential safety hazard was indicated.
Analysis of in total 151 animal manures sampled from selected vegetable farms was done according to a joint strategy at the various research institutes involved. Most commonly, the shiga-toxin producing E. coli (STEC) virulence genes stx2, stx1, and eae intimin were found in the manure samples. The rfbE gene, specific for enterohaemorragic E. coli O157:H7 (EHEC), was found in more than one third of the samples. The chemical properties and bacterial community structures of the samples were investigated and possible correlations between all these parameters were studied.
The vegetable samples analyzed included 1973 lettuce heads (romaine, iceberg, and butter head), 190 spinach plants, 50 carrots, and 50 corn salad plants. All samples were processed in the same way in the various labs participating in the screening for the preparation of DNA extracts and subsequent analysis for pathogenic bacteria. Our study revealed that an unexpected high number of vegetables collected from the selected fields were colonized by bacterial pathogens. However, as enrichment was used prior to PCR-based analysis, the screening results may not pose an implicit threat to the consumer due to possibly low pathogen numbers. Yet, our results stress the need for stringent post-harvest handling and processing procedures in terms of restricting survival and proliferation of pathogens possibly introduced on the field.
Factors that potentially lead to the contamination of organically grown vegetables with human pathogens were studied in greenhouse/growth chamber/phytotron experiments at the various labs participating in the project. In addition, critical control points (CCPs) were evaluated specifically for organic farms that use manure for vegetable production. The hazard analysis was based on the characteristics of the enteropathogens analyzed within the project and on the agricultural practices applied as assessed in interviews with farmers. Another project aim was the development of a conceptual model that quantifies bacterial pathogens in the pathway manure – soil – crop. The model was established based on the knowledge obtained in the PathOrganic project; however, a bottleneck remained regarding the data on manure storage times, fertilizing practices and realistic initial concentrations of pathogens.
A final project workshop was held at FiBL in Frick, where the major outcomes of the screenings and implications for manure management were discussed, forming the basis for the set-up of a leaflet. Finally, the major project outcomes were summed up by FiBL in a leaflet containing recommendations concerning safe vegetable production procedures. Thus, the project results may assist farmers and food processing companies in their endeavours to prevent microbe-mediated contamination of organically grown vegetables.