Attachment of Escherichia coli O157:H7 to lettuce leaf surface and bacterial viability in response to chlorine treatment as demonstrated by using confocal scanning laser microscopy

J Food Prot. 1999 Jan;62(1):3-9. doi: 10.4315/0362-028x-62.1.3.


Confocal scanning laser microscopy was used to observe the location of Escherichia coli O157:H7 on and within lettuce leaves. Sections of leaves (ca. 0.5 by 0.5 cm) were inoculated by submersion in a suspension of E. coli O157:H7 (ca. 10(7) to 10(8) CFU/ml) overnight at 7 degrees C. Fluorescein isothiocyanate-labeled antibody was used to visualize the attached bacteria. E. coli O157:H7 was found attached to the surface, trichomes, stomata, and cut edges. Three-dimensional volume reconstruction of interior portions of leaves showed that E. coli O157:H7 was entrapped 20 to 100 microm below the surface in stomata and cut edges. Agar plate culturing and microscopic observation indicated that E. coli O157:H7 preferentially attached to cut edges, as opposed to the intact leaf surface. Dual staining with fluorescein isothiocyanate-labeled antibody and propidium iodide was used to determine viability of cells on artificially contaminated lettuce leaves after treatment with 20 mg/liter chlorine solution for 5 min. Many live cells were found in stomata and on cut edges following chlorine treatment. E. coli O157:H7 did not preferentially adhere to biofilm produced by Pseudomonas fluorescens on the leaf surface. In contrast to E. coli O157:H7, Pseudomonas adhered to and grew mainly on the intact leaf surface rather than on the cut edges.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Adhesion / physiology*
  • Bacteriological Techniques
  • Biofilms
  • Chlorine / pharmacology*
  • Colony Count, Microbial
  • Disinfection
  • Escherichia coli Infections / microbiology
  • Escherichia coli O157 / drug effects
  • Escherichia coli O157 / growth & development
  • Escherichia coli O157 / physiology*
  • Humans
  • Lettuce / microbiology*
  • Microscopy, Confocal
  • Pseudomonas fluorescens / growth & development


  • Chlorine