Validation of Methods and Microbial Analysis for Advanced Life Support Salad Crops

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Validation of Methods and Microbial Analysis for
Advanced Life Support Salad Crops

• PI Mary Hummerick
• Trainee Paul Lopez II
• Controlled Biological Systems

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Initial Description

• 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.

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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

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Filter being placed on m-FC broth
Radish pulled out of hydroponically grown
system for sampling