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

Cells of Escherichia coli O157:H7 on uninjured and injured surfaces of gree n pepper were inactivated by 0.15-1.2 mg l(-1) ClO2 gas treatments. A membr ane-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 O1 57:H7 on uninjured and injured green pepper surfaces after ClO2 gas treatme nts were visualized using confocal laser scanning microscopy (CLSM) Live an d dead cells of E. coli O157: H7 on pepper surfaces were labeled with a flu orescein isothiocyanate-labeled antibody and propidium iodide, respectively A 7.27 log reduction of E. coli O157: H7 on uninjured green pepper surface s was obtained with a 0.60 mg l(-1) ClO2 gas treatment for 30 min at 20 deg reesC under 90-95% relative humidity. For injured surfaces, a 6.45 log redu ction was achieved with a 1.2 mg l(-1) ClO2 gas treatment Each ClO2 gas tre atment (0.15-1.2 mg l(-1) ClO2) for inoculated bacteria on uninjured surfac es showed significantly move reductions (1.23-4.24 log) than for those on i njured surfaces (P<0.05) The microphotographs of CLSM showed that bacteria preferentially attached to injured surfaces and those bacteria could be pro tected from bacterial reduction by the injuries. This study indicates that ClO2 gas treatment can be a potential effective method of pathogen reductio n for fresh fruits and vegetables. (C) 2000 Academic Press.