The ability of Escherichia coli O157:H7 to penetrate and grow within punctures, fresh-cut surfaces, and calyces of Golden Delicious apples was investigated. A three-strain cocktail of E. coli O157:H7 resistant to ampicillin was used to inoculate fresh and 48-h-old punctures, fresh-cut surfaces, and open or closed calyces. A concentric cutting procedure was used to evaluate depth of penetration within punctures and prevent cross contamination during sampling. Within 2 h, E. coli O157:H7 penetrated vertically through the fresh punctures and 3.4 mm within the underlying parenchyma. After 48 h, E. coli O157: H7 cells penetrated up to 5.5 mm within the punctures and>2.6 mm horizontally away from fresh punctures. However, 48-h-old punctures did not permit penetration beyond their boundaries. Fresh-cut surfaces permitted up to 2.8 mm penetration after 24 h. Onset of growth of E. coli O157:H7 occurred 4 to 8 h postinoculation on fresh punctures and fresh-cut surfaces with populations increasing by 3 logs after 48 h. E. coli O157:H7 penetrated within calyces regardless of the extent of opening or method of inoculation. However, E. coli O157:H7 was never recovered from the inner core of apples. Computed tomography scan imaging revealed that closed calyces effectively prevented penetration of sodium iodide solutions within the calyx cavity. Lack of solution penetration may explain why sanitizing treatments are ineffective in inactivating microbial cells within the calyx. Understanding the role of morphological differences in permitting or restricting bacterial penetration may lead to development of more effective strategies to enhance the safety of fresh horticultural products.

This study was conducted to determine the penetration of 5% trisodium phosphate solution at various depths within punctures and calyces of apples spot inoculated with Escherichia coli O157:H7 and the effect of solution agitation on destruction of the pathogen. Sanitizer solutions containing radiolabeled disodium phosphate (DSP32) were able to penetrate apple tissues through punctures and calyx cavities. However, agitation of the solutions did not result in significantly greater penetration in these areas (P > 0.05). Overall, there were 1.57- and 1.1-log reductions of pathogen cells within 4-h-old punctures treated with and without trisodium phosphate solution agitation, respectively. Sanitizer solutions were effective in destroying pathogen cells residing within the upper 4.2-mm region of the punctures. Destruction of pathogen cells within open and closed calyces occurred mainly within the basin and the upper 3 mm of the calyx cavity. Treatment with agitated sanitizer solution resulted in a 0.67-log reduction in pathogen concentration within open calyces. In contrast, treatment of closed calyces resulted in a 1.37-log reduction, mainly within the basin. Washing with water alone appeared to result in further penetration of the cells within calyces without significantly reducing the number of pathogen cells (P > 0.05). To develop more effective methods for reducing contamination on produce, it is important to know the extent of sanitizer penetration and its effect on destruction of pathogens.