Validation of Methods and Microbial Analysis for Advanced Life Support Salad Crops
This research evaluated and compared methods for the isolation of Escherichia coli and Staphylococcus aureus in broth cultures and inoculated and processed edible plant samples (lettuce, onion, and radish). Microbial monitoring of chamber grown salad crops was done to evaluate baseline microbial quality and density on edible portions of plants.
Above: Radish pulled out of hydroponically grown system for sampling
Main Story
The methods for the isolation of Escherichia coli and Staphylococcus aureus in broth cultures and hydroponically grown plant samples (lettuce, onion, and radish) were evaluated and compared. Broth cultures of S. aureus and E. coli were grown and serially diluted. Each dilution was filtered. Live/dead and acridine orange direct counts were performed on cultures. Plant samples were collected in sterile sample bags and weighed. Samples were inoculated with a known number of E. coli and S. aureus cells. A lower number (in some cases a one to two log decrease) of E. coli was detected using plating (Petrifilm) and membrane filtration methods in some of the inoculated plants as compared to the inoculum direct count. This was not evident in the broth culture samples that were run as a control. The same decrease in number was not seen in the samples analyzed for S. aureus. This research helped determine the affect on detection and numbers of bacteria in the sample due to plant components before and after blending. This information is important in selecting methods of analysis for food safety of fresh salad crops grown in ALS systems.
Above: Filter being placed on m-FC broth
Author: Paul Lopez II, Controlled Biological Systems
North Carolina Agricultural and Technical University
Principal Investigators: Mary Hummerick, Dynamac Corporation
Click here to download a printable Microsoft PowerPoint version of this research.
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