Inactivation of Escherichia coli O157:H7 on surface-uninjured and -injured green pepper (Capsicum annuum L.) by chlorine dioxide gases demonstrated by confocal laser scanning microscopy

Cells of Escherichia coli O157:H7 on uninjured and injured surfaces of green pepper were inactivated by 0.15-1.2 mg l(-1) ClO2 gas treatments. A membrane-surface-plating method was used for resuscitation and enumeration of E. co ii O157: H7 treated with ClO2. The location and viability of E. coli O157:H7 on uninjured and injured green pepper surfaces after ClO2 gas treatments were visualized using confocal laser scanning microscopy (CLSM) Live and dead cells of E. coli O157: H7 on pepper surfaces were labeled with a fluorescein isothiocyanate-labeled antibody and propidium iodide, respectively A 7.27 log reduction of E. coli O157: H7 on uninjured green pepper surfaces was obtained with a 0.60 mg l(-1) ClO2 gas treatment for 30 min at 20 degreesC under 90-95% relative humidity. For injured surfaces, a 6.45 log reduction was achieved with a 1.2 mg l(-1) ClO2 gas treatment Each ClO2 gas treatment (0.15-1.2 mg l(-1) ClO2) for inoculated bacteria on uninjured surfaces showed significantly move 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 ClO2 gas treatment can be a potential effective method of pathogen reduction for fresh fruits and vegetables. (C) 2000 Academic Press.