Evidence of Salmonella Internalization into Fresh Mangos during Simulated Postharvest Insect Disinfestation Procedures

Abstract

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°C for 90 min and then immersed in 21°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°C water containing 107 CFU/ml Salmonella Enteritidis expressing constitutive green fluorescent protein. Fruit was then stored at 10, 20, or 30°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.