Surveying Pathogenic Bacteria in Vegetables

Summary

Bacterial pathogens have increasingly been identified as disease causing agents in vegetable-linked outbreaks. Consumers nowadays show higher demands for fresh or minimally processed fruits and vegetables, and at the same time potential sources of pathogen infestation are increasing due to the more frequent use of animal manures as fertilizers in organic than in conventional agriculture. On the other hand, a higher antagonistic potential against invading pathogens is implicated from the more diverse microbiota in organic soils. Vegetable-associated outbreaks in Europe are not well documented, and guidelines are missing for reducing risks of pathogen infestation. Thus, a survey on organically grown vegetables has been carried out by the “PathOrganic” consortium in five countries. In total, 4620 plants of lettuce, 1900 plants of spinach and 500 carrots from 14 fields were collected and by using PCR based detection methods were analyzed for the prevalence of pathogenic E. coli, Salmonella sp., Staphylococcus aureus, Listeria sp. and Campylobacter spp. Common protocols were used regarding harvest and sample preparation; and molecular analyses were shared among labs according to expertise. Preceding the vegetable screenings, animal manures of various origin used for fertilizing the fields were analyzed for the presence of the same pathogens, aimed at pin-pointing potential sources of contamination. Results of the vegetable and manure surveys are presented and the concept of microbiological risk assessment followed in the project is discussed. Besides yielding a large dataset concerning pathogen infestation of vegetables and manures, the screenings provided a collection of vegetable-derived pathogen isolates available for further analysis. Together with information obtained in experimental assays, the survey results may enlarge our understanding of vegetable-associated human pathogenic bacteria and their interrelations with common microbial colonizers of plants and soils.