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Interaction
of Escherichia coli with growing salad spinach plants.
J Food Prot. 2003
Oct;66(10):1790-7.
Warriner K, Ibrahim F, Dickinson M, Wright C, Waites WM.
Division of Food Sciences, School of Biosciences, University of Nottingham,
Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK.
In this study, the interaction of a bioluminescence-labeled Escherichia coli
strain with growing spinach plants was assessed. Through bioluminescence
profiles, the direct visualization of E. coli growing around the roots of
developing seedlings was accomplished. Subsequent in situ glucuronidase (GUS)
staining of seedlings confirmed that E. coli had become internalized within root
tissue and, to a limited extent, within hypocotyls. When inoculated seeds
were sown in soil microcosms and cultivated for 42 days, E. coli was recovered
from the external surfaces of spinach roots and leaves as well as from
surface-sterilized roots. When 20-day-old spinach seedlings (from uninoculated
seeds) were transferred to soil inoculated with E. coli, the bacterium became
established on the plant surface, but internalization into the inner root tissue
was restricted. However, for seedlings transferred to a hydroponic system
containing 10(2) or 10(3) CFU of E. coli per ml of the circulating nutrient
solution, the bacterium was recovered from surface-sterilized roots, indicating
that it had been internalized. Differences between E. coli interactions in the
soil and those in the hydroponic system may be attributed to greater
accessibility of the roots in the latter model. Alternatively, the presence of a
competitive microflora in soil may have restricted root colonization by E. coli.
The implications of this study's findings with regard to the microbiological
safety of minimally processed vegetables are discussed.
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