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Cells of Escherichia coliO157:H7 on uninjured and injured surfaces of green pepper were inactivated by 0·15–1·2 mg l−1ClO2gas treatments. A membrane-surface-plating method was used for resuscitation and enumeration of E. coliO157:H7 treated with ClO2. The location and viability ofE. coliO157:H7 on uninjured and injured green pepper surfaces after ClO2gas treatments were visualized using confocal laser scanning microscopy (CLSM). Live and dead cells of E. coliO157:H7 on pepper surfaces were labeled with a fluorescein isothiocyanate-labeled antibody and propidium iodide, respectively. A 7·27 log reduction of E. coliO157:H7 on uninjured green pepper surfaces was obtained with a 0·60 mg l−1ClO2gas treatment for 30 min at 20°C under 90–95% relative humidity. For injured surfaces, a 6·45 log reduction was achieved with a 1·2 mg l−1ClO2gas treatment. Each ClO2gas treatment (0·15–1·2 mg l−1ClO2) for inoculated bacteria on uninjured surfaces showed significantly more reductions (1·23–4·24 log) than for those on injured surfaces (P<0·05). The microphotographs of CLSM showed that bacteria preferentially attached to injured surfaces and those bacteria could be protected from bacterial reduction by the injuries. This study indicates that ClO2gas treatment can be a potential effective method of pathogen reduction for fresh fruits and vegetables.

The effects of washing and chlorine dioxide (ClO2) gas treatment on survivability and attachment of Escherichia coliO157: H7 C7927 to uninjured and injured green pepper surfaces were investigated using scanning electron microscopy and colony enumeration methods. Escherichia coliO157: H7 preferentially attached to coarse and porous intact surfaces and injured surfaces. The bacterial attachment to injured green pepper surfaces may be determined mainly by the hydrophilic properties of the injured surfaces and might not be assisted by the exocellular polymers of the bacteria. Injuries to the wax layer, the cuticle and underlying tissues increased bacterial adhesion, growth, and resistance to washing and disinfecting treatments. No significant growth of E. coliO157: H7 was found on uninjured surfaces after inoculation and incubation for 24 h at 37°C, whereas significant growth and multiplication were found on injured surfaces (P<0·05). ClO2gas treatment was more effective as a disinfecting method than water washing. Using a membrane-plating method for resuscitation and enumeration of ClO2-treated E. coliO157: H7 on surface-injured green peppers, 3·03±0·02 and 6·45 ±0·02 log reductions were obtained after treatments by 0·62 and 1·24 mg l−1ClO2, respectively, for 30 min at 22°C and 90–95% relative humidity. In contrast, water washing achieved log reductions of 1·5±0·05–1·67±0·10 on injured surfaces and 2·44±0·04 on uninjured surfaces.