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Published on: April 9, 2018
Internalization of bioluminescent Escherichia coli and Salmonella Montevideo in growing bean sprouts
K Warriner1, S Spaniolas, M Dickinson
1Division of Food Sciences, School of Biosciences, University of Nottingham, Leicestershire, UK.
Aims:
Investigate the interaction of bioluminescent Escherichia coli and Salmonella Montevideo with germinating mung bean sprouts.
Methods And Results:
E. coli or Salm. Montevideo introduced on mung beans became established both internally and externally on sprouts after the initial 24 h germinating period. In both cases the inoculated bacterium formed the predominant microflora on the sprouted beans throughout. From the bioluminescent profile of inoculated sprouting beans, bacterial growth was found to be in close proximity to the roots but not on the hypocotyls. Clumps (biofilms) of cells with low viability were observed within the grooves between epidermal cells on hypocotyls. Treatment with 20,000 ppm sodium hypochlorite removed the majority of bacteria from the surface of hypocotyls although nonviable single cells were occasionally observed. However, viable bacteria were recovered from the apoplastic fluid, and extracts of surface-sterilized sprouts indicating that the internal bacterial populations had been protected. This was confirmed using in situ beta-glucuronidase staining of surface-sterilized sprouts where cleaved enzyme substrate (by the action of internalized E. coli) was visualized within the plant vascular system.
Conclusions:
E. coli or Salmonella present on seeds become internalized within the subsequent sprouts and cannot be removed by postharvest biocidal washing.
Significance And Impact Of The Study:
Mung bean production should be carefully controlled to prevent contamination occurring in order to minimize the health risk associated with raw bean sprouts.
Insights
Escherichia coli and Salmonella Montevideo can internalize within mung bean sprouts, establishing a predominant microflora. Post-harvest washing with sodium hypochlorite does not eliminate these internalized bacteria, posing a health risk.
Area of Science:
- Food microbiology
- Plant-microbe interactions
Background:
- Raw bean sprouts are a common vehicle for foodborne illnesses.
- Understanding bacterial internalization in sprouts is crucial for food safety.
Purpose of the Study:
- To investigate the interaction of bioluminescent Escherichia coli and Salmonella Montevideo with germinating mung bean sprouts.
- To determine the efficacy of post-harvest washing in removing internalized bacteria.
Main Methods:
- Inoculation of mung bean seeds with bioluminescent E. coli and S. Montevideo.
- Monitoring bacterial colonization during germination using bioluminescence.
- Assessing bacterial removal using sodium hypochlorite treatment.
- Confirming internalization via in situ staining.
Main Results:
- Inoculated bacteria (E. coli, S. Montevideo) colonized sprouts internally and externally, forming the predominant microflora.
- Bacterial growth was observed near roots, with biofilms on hypocotyls.
- Sodium hypochlorite treatment reduced surface bacteria but viable internalized bacteria remained in apoplastic fluid and sprout extracts.
- In situ staining confirmed E. coli internalization within the plant vascular system.
Conclusions:
- Escherichia coli and Salmonella on mung bean seeds are internalized by sprouts and persist after washing.
- Effective control during mung bean production is essential to mitigate health risks associated with raw sprouts.
