title: Escherichia coli survival in lettuce fields following its introduction through different irrigation systems.
abstract: OBJECTIVE
  This study aimed to assess the contamination risk of Escherichia coli in commercial lettuce grown under three different irrigation systems (overhead sprinkler, subsurface drip and surface furrow).
  
  
  RESULTS
  Three replicated field trials were conducted. In an initial trial, we consistently observed higher mesophilic bacteria counts under sprinkler irrigation but visual quality was found to be dependent on the water potential of leaves at harvest. Further, in the other two trials, E. coli K-12 strains LMM1010 and ATCC 25253, was injected into the water stream of the different irrigation systems to determine survival in the field. Results showed that product samples were positive for E. coli up to 7 days when using sprinkler irrigation, whereas only one product sample was found positive for E. coli when using other irrigation methods. Survival of bacteria in soil persisted longer in furrow-irrigated areas, ranging from an estimated 17 days in winter months to 5 days during the warmer summer periods. This finding combined with results from a parallel 3-year survey of canal waters indicate that while highest risk of finding E. coli in irrigation water is in warmer months, the survival in soil is lower during the same time period.
  
  
  CONCLUSIONS
  Our results in a study set under common commercial conditions confirmed the enhanced risk of E. coli contamination when using sprinkle irrigation. Furthermore, E. coli persistence in furrow-irrigated soil validates the importance of an early irrigation termination for both sprinkler and furrow methods.
authors.affiliation: Yuma Agricultural Center, The University of Arizona, Yuma, AZ 85364, USA. jfonseca@ag.arizona.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Fonseca
authors.forename: S D
authors.initials: SD
authors.lastname: Fallon
authors.forename: C A
authors.initials: CA
authors.lastname: Sanchez
authors.forename: K D
authors.initials: KD
authors.lastname: Nolte
mesh_terms: D057914:Agricultural Irrigation; D004926:Escherichia coli / Q000302:isolation & purification / Q000502:physiology*; D005516:Food Microbiology; D018545:Lactuca / Q000382:microbiology*; D050296:Microbial Viability; D018515:Plant Leaves / Q000382:microbiology; D012621:Seasons; D012988:Soil Microbiology; D014871:Water Microbiology