Surface and internalized Escherichia coli O157:H7 on field-grown spinach and lettuce treated with spray-contaminated irrigation water.
Numerous field studies have revealed that irrigation water can contaminate the surface of plants; however, the occurrence of pathogen internalization is unclear. This study was conducted to determine the sites of Escherichia coli O157:H7 contamination and its survival when the bacteria were applied through spray irrigation water to either field-grown spinach or lettuce. To differentiate internalized and surface populations, leaves were treated with a surface disinfectant wash before the tissue was ground for analysis of E. coli O157:H7 by direct plate count or enrichment culture. Irrigation water containing E. coli O157:H7 at 10(2), 10(4), or 10(6) CFU/ml was applied to spinach 48 and 69 days after transplantation of seedlings into fields. E. coli O157:H7 was initially detected after application on the surface of plants dosed at 10(4) CFU/ml (4 of 20 samples) and both on the surface (17 of 20 samples) and internally (5 of 20 samples) of plants dosed at 10(6) CFU/ml. Seven days postspraying, all spinach leaves tested negative for surface or internal contamination. In a subsequent study, irrigation water containing E. coli O157:H7 at 10(8) CFU/ml was sprayed onto either the abaxial (lower) or adaxial (upper) side of leaves of field-grown lettuce under sunny or shaded conditions. E. coli O157:H7 was detectable on the leaf surface 27 days postspraying, but survival was higher on leaves sprayed on the abaxial side than on leaves sprayed on the adaxial side. Internalization of E. coli O157:H7 into lettuce leaves also occurred with greater persistence in leaves sprayed on the abaxial side (up to 14 days) than in leaves sprayed on the adaxial side (2 days).
Center for Food Safety, Department of Food Science and Technology, 1109 Experiment Street, University of Georgia, Griffin, Georgia 30223, USA. mericks@uga.edu
Marilyn C
MC
Erickson
Cathy C
CC
Webb
Juan Carlos
JC
Diaz-Perez
Sharad C
SC
Phatak
John J
JJ
Silvoy
Lindsey
L
Davey
Alison S
AS
Payton
Jean
J
Liao
Li
L
Ma
Michael P
MP
Doyle
D000383:Agriculture; D000890:Anti-Infective Agents / Q000494:pharmacology; D001422:Bacterial Adhesion / Q000502:physiology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D019453:Escherichia coli O157 / Q000502:physiology*; D005506:Food Contamination / Q000032:analysis* / Q000517:prevention & control; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D018545:Lactuca / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D018724:Spinacia oleracea / Q000382:microbiology*; D014871:Water Microbiology
D000890:Anti-Infective Agents