title: The endophytic lifestyle of Escherichia coli O157:H7: quantification and internal localization in roots.
abstract: The foodborne pathogen Escherichia coli O157:H7 is increasingly associated with fresh produce (fruit and vegetables). Bacterial colonization of fresh produce plants can occur to high levels on the external tissue but bacteria have also been detected within plant tissue. However, questions remain about the extent of internalization, its molecular basis, and internal location of the bacteria. We have determined the extent of internalization of E. coli O157:H7 in live spinach and lettuce plants and used high-resolution microscopy to examine colony formation in roots and pathways to internalization. E. coli O157:H7 was found within internal tissue of both produce species. Colonization occurred within the apoplast between plant cells. Furthermore, colonies were detected inside the cell wall of epidermal and cortical cells of spinach and Nicotiana benthamiana roots. Internal colonization of epidermal cells resembled that of the phytopathogen Pectobacterium atrosepticum on potato. In contrast, only sporadic cells of the laboratory strain of E. coli K-12 were found on spinach, with no internal bacteria evident. The data extend previous findings that internal colonization of plants appears to be limited to a specific group of plant-interacting bacteria, including E. coli O157:H7, and demonstrates its ability to invade the cells of living plants.
authors.affiliation: The James Hutton Institute, Dundee, UK.
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Wright
authors.forename: Sean
authors.initials: S
authors.lastname: Chapman
authors.forename: Kara
authors.initials: K
authors.lastname: McGeachy
authors.forename: Sonia
authors.initials: S
authors.lastname: Humphris
authors.forename: Emma
authors.initials: E
authors.lastname: Campbell
authors.forename: Ian K
authors.initials: IK
authors.lastname: Toth
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Holden
mesh_terms: D015169:Colony Count, Microbial; D060026:Endophytes; D004926:Escherichia coli / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D019453:Escherichia coli O157 / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D005506:Food Contamination; D005516:Food Microbiology; D054884:Host-Pathogen Interactions; D006801:Humans; D018545:Lactuca / Q000166:cytology / Q000382:microbiology*; D046529:Microscopy, Electron, Transmission; D044043:Pectobacterium / Q000166:cytology / Q000254:growth & development / Q000502:physiology; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology*; D030821:Plants, Genetically Modified; D058441:Rhizosphere; D012988:Soil Microbiology; D011198:Solanum tuberosum / Q000166:cytology / Q000382:microbiology; D018724:Spinacia oleracea / Q000166:cytology / Q000382:microbiology*; D014026:Nicotiana / Q000166:cytology / Q000382:microbiology; D014675:Vegetables / Q000382:microbiology*