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Identification of the cellular
location of internalized Escherichia coli O157:H7 in mung bean, Vigna radiata,
by immunocytochemical techniques
06.aug.11
Journal of Food Protection®, Volume 74, Number 8, August 2011 , pp. 1224-1230(7)
Deering, Amanda J., Pruitt, Robert E., Mauer, Lisa J, Reuhs, Bradley L.
Abstract:
Escherichia coli O157:H7 has been associated with numerous outbreaks involving
fresh produce. Previous studies have shown that bacteria can be internalized
within plant tissue and that this can be a source of protection from
antimicrobial chemicals and environmental conditions. However, the types of
tissue and cellular locations the bacteria occupy in the plant following
internalization have not been addressed. In this study, immunocytochemical
techniques were used to localize internalized E. coli O157:H7 expressing green
fluorescent protein in germinated mung bean (Vigna radiata) hypocotyl tissue
following contamination of intact seeds. An average of 13 bacteria per mm3 were
localized within the sampled tissue. The bacteria were found to be associated
with every major tissue and corresponding cell type (cortex, phloem, xylem,
epidermis, and pith). The cortical cells located on the outside of the vascular
bundles contained the majority of the internalized bacteria (61%). In addition,
the bacteria were localized primarily to the spaces between the cells (apoplast)
and not within the cells. Growth experiments were also performed and
demonstrated that mung bean plants could support the replication of bacteria to
high levels (107 CFU per plant) following seed contamination and that these
levels could be sustained over a 12-day period. Therefore, E. coli O157:H7 can
be internalized in many different plant tissue types after a brief seed
contamination event, and the bacteria are able to grow and persist within the
plant.
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