Potential for internalization, growth, and survival of Salmonella and Escherichia coli O157:H7 in oranges.

Internalization potential, survival, and growth of human pathogens within oranges were investigated in a series of laboratory experiments. Submerging oranges into dye solutions at various temperature differentials was used to assess internalization potential. Conditions in which dye internalization was observed were further studied by applying Escherichia coli O157:H7 or Salmonella onto the stem scar, subjecting the oranges to a temperature differential, juicing, and measuring numbers of pathogens in the resulting juice. Pathogens for growth and survival studies were applied to or injected into simulated peel punctures. Oranges with small peel holes of selected sizes were also placed into solutions containing these pathogens. Bacterial survival was also evaluated in orange juice at 4 and 24 degrees C. Oranges internalized pathogens at a frequency of 2.5 to 3.0%, which mirrored dye internalization frequency (3.3%). Pathogens were internalized at an uptake level of 0.1 to 0.01% of the challenge applied. Bacteria grew within oranges at 24 degrees C, but not at 4 degrees C. Thirty-one percent of oranges with 0.91-mm surface holes showed pathogen uptake, whereas 2% of oranges with 0.68-mm holes showed pathogen uptake. Pathogens added to fresh orange juice and incubated at 24 degrees C declined 1 log CFU/ml within 3 days. These results suggest that internalization, survival, and growth of human bacterial pathogens can occur within oranges intended for producing unpasteurized juice.

Evidence of Salmonella internalization into fresh mangos during simulated postharvest insect disinfestation procedures.

A recent U.S. salmonellosis outbreak was epidemiologically associated with consumption of imported fresh mangos. Studies were conducted to simulate the commercial heat disinfestation method used to eliminate tephritid fly larvae from mangos, as well as subsequent product cooling procedures, to assess whether this process promotes internalization of Salmonella into mangos. The experimental parameters were chosen to mimic the disinfestation method used by the South American producer/packer implicated in the recent outbreak. Untreated domestically grown immature and ripened Tommy Atkins variety mangos were immersed in water at 47 degrees C for 90 min and then immersed in 21 degrees C water containing brilliant blue FD&C no. 1 dye for 10 min. After dye internalization potential was established (67%), the same experiment was performed using 21 degrees C water containing 10(7) CFU/ml Salmonella Enteritidis expressing constitutive green fluorescent protein. Fruit was then stored at 10, 20, or 30 degrees C for up to 1 week. Immature and ripened mangos were positive for Salmonella internalization at a frequency of 80 and 87%, respectively. Internalization frequency into the stem-end segment (83%) was significantly higher (P < 0.05) than internalization into the middle-side (19%) or blossom-end (9%) segments of the fruit. Salmonella was detected in the mango pulp after 1 week of incubation. The degree of fruit ripeness, posttreatment holding temperature, or duration of storage had no significant effect (P > 0.05) on internalization frequency or survival of Salmonella inside mangos. This study illustrates the high potential for pathogen internalization if heat-disinfested mangos are cooled using contaminated water.

Growth, Injury, and Survival Potential of Yersinia enterocolitica . Listeria monocytogenes , and Staphylococcus aureus in Brine Chiller Conditions †.

A model brine system was used to evaluate growth, injury, and survival potential of Yersinia enterocolitica . Listeria monocytogenes , and Staphylococcus aureus . Each strain was incubated for up to 30 days at -12 to 28°C in brain heart infusion broth containing 0.5 to 20% NaCl. Samples were enumerated on a dual agar plating system to assess growth and injury. Y. enterocolitica grew at -2°C in 0.5% brine and at 5°C in 5% NaCl. L. monocytogenes grew at 5°C in 5% NaCl and at 12°C in 9% NaCl. S. aureus grew at 12°C in 5% NaCl. Significant injury was observed for two of the pathogens, but not for L. monocytogenes . Bacteriostatic or lethal conditions were maintained for the three organisms at -2°C and 9% NaCl. While lethal NaCl and temperature combinations were defined for Y. enterocolitica and S. aureus . L. monocytogenes survived for 30 days at -12°C in 20% NaCl. This study provides safety criteria and recommendations for use in the operation of recycle brine systems for cooling processed foods.