title: Identification of the cellular location of internalized Escherichia coli O157:H7 in mung bean, Vigna radiata, by immunocytochemical techniques.
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 mm(3) 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 (10(7) 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.
authors.affiliation: Department of Food Science, Purdue University, West Lafayette, Indiana 47907, USA. adeering@purdue.edu
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Deering
authors.forename: Robert E
authors.initials: RE
authors.lastname: Pruitt
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Mauer
authors.forename: Bradley L
authors.initials: BL
authors.lastname: Reuhs
mesh_terms: D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004196:Disease Outbreaks / Q000517:prevention & control; D019453:Escherichia coli O157 / Q000254:growth & development / Q000302:isolation & purification*; D007887:Fabaceae / Q000254:growth & development / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D049452:Green Fluorescent Proteins; D006801:Humans; D007150:Immunohistochemistry
chemical_list: D049452:Green Fluorescent Proteins