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

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. 107to 108CFU/ml) overnight at 7°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 μm 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 w...