Biotic and abiotic variables affecting internalization and fate of Escherichia coli O157:H7 isolates in leafy green roots.
Preharvest internalization of Escherichia coli O157:H7 into the roots of leafy greens is a food safety risk because the pathogen may be systemically transported to edible portions of the plant. In this study, both abiotic (degree of soil moisture) and biotic (E. coli O157:H7 exposure, presence of Shiga toxin genes, and type of leafy green) factors were examined to determine their potential effects on pathogen internalization into roots of leafy greens. Using field soil that should have an active indigenous microbial community, internalized populations in lettuce roots were 0.8 to 1.6 log CFU/g after exposure to soil containing E. coli O157:H7 at 5.6 to 6.1 log CFU/g. Internalization of E. coli O157:H7 into leafy green plant roots was higher when E. coli O157:H7 populations in soil were increased to 7 or 8 log CFU/g or when the soil was saturated with water. No differences were noted in the extent to which internalization of E. coli O157:H7 occurred in spinach, lettuce, or parsley roots; however, in saturated soil, maximum levels in parsley occurred later than did those in spinach or lettuce. Translocation of E. coli O157:H7 from roots to leaves was rare; therefore, decreases observed in root populations over time were likely the result of inactivation within the plant tissue. Shiga toxin-negative (nontoxigenic) E. coli O157:H7 isolates were more stable than were virulent isolates in soil, but the degree of internalization of E. coli O157:H7 into roots did not differ between isolate type. Therefore, these nontoxigenic isolates could be used as surrogates for virulent isolates in field trials involving internalization.
Center for Food Safety, Department of Food Science and Technology, University of Georgia, Griffin, Georgia 30223-1797, USA. mericks@uga.edu.
Marilyn C
MC
Erickson
Center for Food Safety, Department of Food Science and Technology, University of Georgia, Griffin, Georgia 30223-1797, USA.
Cathy C
CC
Webb
Center for Food Safety, Department of Food Science and Technology, University of Georgia, Griffin, Georgia 30223-1797, USA.
Lindsey E
LE
Davey
Center for Food Safety, Department of Food Science and Technology, University of Georgia, Griffin, Georgia 30223-1797, USA.
Alison S
AS
Payton
Department of Crops and Soil Science, 1109 Experiment Street, University of Georgia, Griffin, Georgia 30223-1797, USA.
Ian D
ID
Flitcroft
Center for Food Safety, Department of Food Science and Technology, University of Georgia, Griffin, Georgia 30223-1797, USA.
Michael P
MP
Doyle
D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000145:classification / Q000254:growth & development / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D018545:Lactuca / Q000254:growth & development / Q000382:microbiology; D028528:Petroselinum / Q000254:growth & development / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology*; D012988:Soil Microbiology; D018724:Spinacia oleracea / Q000254:growth & development / Q000382:microbiology; D014675:Vegetables / Q000382:microbiology*