Influence of Punctures, Cuts, and Surface Morphologies of Golden Delicious Apples on Penetration and Growth of Escherichia coli O157:H7

Abstract

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 3.4mm within the underlying parenchyma. After 48 h, E. coli O157: H7 cells penetrated up to 5.5mm within the punctures and >2.6mm horizontally away from fresh punctures. However, 48-h-old punctures did not permit penetration beyond their boundaries. Fresh-cut surfaces permitted up to 2.8mm 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.