Survival, growth, and control of Escherichia coli O157:H7 and Listeria monocytogenes on fresh produce and cooked poultry products

This study investigates the ability of enterohemorrhagic Escherichia coli O157:H7 (EHEC) to survive and grow in wounded Red Delicious apple tissue by using transmission electron microscopy (TEM), tissue printing or bacterial counts. By day 21 the EHEC apple and human isolate during temperature abuse had higher viable counts than at 4°C. At 4°C the counts for the apple isolates were significantly greater than for the human isolate. EHEC was able to spread further from the site of the wound of the apple when submerged in EHEC contaminated dH₂O than by droplet inoculation. TEM observations showed the human and apple cider isolates grown in apple tissue contained granules, vesicles, and electron translucent areas in their cytoplasm. EHEC can grow and survive better in apple tissue when temperature abused. Washing solutions containing NaCl/NaHCO₃ or cetylpyridinium chloride (CPC) were evaluated for removal of EHEC or L. monocytogenes (Lm) from the surfaces of chopped lettuce. A rinse of 0.8 to 1% each of NaCl/NaHCO₃ (pH 8.0) reduced counts of EHEC by about 2.5 log CFU/g. A concentration of just 0.2% CPC was needed to reduce a 5.6 log inoculum of Lm to non-detectable levels whereas a higher concentration of 0.8% CPC was needed to cause the same reductions of EHEC counts. A rinse solution of NaCl/NaHCO₃ or CPC, will allow consumers and food service providers a useful treatment to reduce levels of EHEC or Lm on fresh produce. The inhibitory activities of nisin added to zein edible films coated onto ready-to-eat chicken were investigated for protection against Lm. Meat samples inoculated with Lm were dipped into an edible zein film (Z) dissolved in either propylene glycol (ZP) or ethanol (ZE), with and without added nisin (N) (1000 IU/g) and/or 1% calcium propionate (CP). Using lower challenge levels of 2.7 log CFU/g, Lm was reduced to non-detectable levels at 4°C with the ZEN, ZENCP, or ZPNCP films from day 0 to day 24 whereas the controls increased to log 8.0. Zein edible films with nisin and calcium propionate can prevent the growth of Lm cells on ready-to-eat chicken breast.