|La Borde, Luke|
Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2005
Publication Date: 2/1/2006
Citation: Fatemi, P., Knabel, S.J., La Borde, L.F., Patton, J., Sapers, G.M., Annous, B.A. 2006. Influence of punctures, cuts and apple surface morphologies on penetration and growth of escherichia coli o157:h7. Journal of Food Protection. 69(2):267-275. Interpretive Summary: Outbreaks of foodborne illness have been associated with the presence of Escherichia coli O157:H7, a human pathogen, on fresh fruits and vegetables. This organism can cause serious illness in adults, and may cause kidney failure in children. Conventional washing and sanitizing treatments have limited efficacy in inactivating and/or reducing E. coli O157:H7 populations on apples. This limited efficacy is attributed to poor contact between the sanitizing agents and pathogenic cells attached to inaccessible sites on the produce surfaces such as calyx and stem regions of an apple. Our objectives were to determine the extent of penetration and growth of this human pathogen within punctured and fresh-cut apple surfaces, and to determine the ability of a sanitizing solution to penetrate the calyx region of an apple. Results showed that this human pathogen was able initially to infiltrate up to 3.4 mm into the flesh of fresh punctures and fresh-cut surfaces of an apple, but no infiltration occurred when inoculation was done at 48 h after wounding. Onset of growth of this human pathogen occurred 4-8 h post inoculation on fresh puncture and fresh-cut surfaces. While E. coli O157:H7 cells penetrated within open and closed calyces of apples, sodium iodide solution (representing a sanitizer) was not able to penetrate closed calyces. This lack of solution penetration may explain the inability of sanitizing solution to remove and/or inactivate bacterial cells within these regions. Understanding the role of morphological features in permitting or restricting penetration to bacteria or sanitizers should lead to the development of more effective strategies to enhance the safety of fresh produce.
Technical 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 3.4 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 4-8 h post inoculation 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. CT-scan imaging revealed that closed calyces effectively prevented penetration of sodium iodide (NaI) solutions within the calyx cavity. Lack of solution penetration may explain why sanitizing treatments are ineffective in inactivating microbial destroying 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.