Understanding microbial populations on fresh produce

Investigator: Robert Pruitt (Department of Botany and Plant Pathology)

Project Report 2012 - 2013

Food safety outbreaks linked to consumption of leafy greens are an increasing concern. Produce is often consumed raw, and while many sanitizers are highly effective on the majority of produce samples, they fail to effectively kill pathogens and/or spoilage microorganisms on some leaf samples. These outliers have the potential to cause quality or safety problems, with large economic consequences; however, studies that report average population reductions following sanitation treatments miss capturing this information. ARS-funded researchers at Purdue University's Center for Food Safety Engineering in West Lafayette, Indiana, established and optimized experimental protocols for: 1) the reliable and consistent isolation of bacteria and bacterial DNA from fresh produce samples, 2) selective enrichment and isolation of pathogens from those samples using FDA approved methods, 3) amplification and sequencing of DNA markers for verifying the identity of bacterial colonies isolated on selective media and 4) using next generation metagenomic sequencing to enumerate and classify bacterial species isolated from fresh produce. Results revealed the bacterial community associated with fresh produce to be complex and variable. Although most of the communities examined are dominated by just two genera of bacteria (Pseudomonas and Flavobacterium), several hundred genera of bacteria are present in smaller numbers. The communities observed on spinach and lettuce are markedly different from one another, and they change in different ways following sanitization and/or cold storage. Using metagenomic sequencing methods to characterize the changes in bacterial communities in response to post-harvest treatments will generate results that will allow us to understand the effects of those treatments on both food safety and spoilage and support efforts to enhance the safety of fresh produce to prevent future outbreaks.

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