The effects of washing and chlorine dioxide gas on survival and attachment of Escherichia coli O157: H7 to green pepper surfaces

The effects of washing and chlorine dioxide (ClO2) gas treatment on survivability and attachment of Escherichia coli O157:H7 C7927 to uninjured and injured green pepper surfaces were investigated using scanning electron microscopy and colony enumeration methods. Escherichia coli O157: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. coli O157:H7 was found on uninjured surfaces after inoculation and incubation for 24 h at 37 degrees C, whereas significant growth and multiplication were found on injured surfaces (P < 0.05). ClO2 gas treatment was more effective as a disinfecting method than water washing. Using a membrane-plating method for resuscitation and enumeration of ClO2-treated E. coli O157: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(-1) ClO2, respectively, for 30 min at 22 degrees C and 90-95% relative humidify, 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. (C) 2000 Academic Press.