P1-188 Fate of Escherichia coli O157:H7, Salmonella and Listeria monocytogenes on the Surface of Whole Cantaloupes and Watermelons during Storage

Sunday, July 26, 2015
Exhibit Hall (Oregon Convention Center)
Loretta Friedrich, University of Florida, Lake Alfred, FL
Michelle Danyluk, University of Florida, Lake Alfred, FL
Lawrence Goodridge, Colorado State University, Fort Collins, CO
Introduction: Recent outbreaks linked to whole melons highlight the importance of understanding the fate of pathogens on melon surfaces at various temperatures.

Purpose: The objective of this research was to quantify the fate of Escherichia coli O157:H7, Salmonella and Listeria monocytogenes on the surface of whole cantaloupes and watermelons.

Methods: Rifampicin-resistant Escherichia coli O157:H7, Salmonella, or L. monocytogenes (ca. 103 CFU/3.1 cm2) cocktails were spot inoculated on the sun-side of whole Athena cantaloupe or watermelons and allowed to dry for 1 h (n = 6). Melons were stored at 4, 10, 15, 20, or 25°C, and sampled up to 21 days. At each time point, the inoculated area (3.1 cm2) was excised, stomached with 10 ml of buffer, and pathogen populations were enumerated on both selective and nonselective media supplemented with rifampicin.

Results: Salmonella on both melon surfaces, and Escherichia coli O157:H7 on watermelon, declined under all experimental conditions. Escherichia coli O157:H7 on cantaloupe held at 4 and 10°C decreased, but populations increased at 15, 20, and 25°C storage; maximum growth occurred when cantaloupe was stored at 25°C for 3 days (4.9 log CFU/3.1 cm2). L. monocytogenes declined on watermelon at 4, 10 and 15°C, but grew on watermelon held at 20 and 25°C, reaching maximum populations at 7 days of storage (4.2 and 4.5 log CFU/3.1 cm2, respectively). L. monocytogenes inoculated onto cantaloupe increased regardless of storage temperature; increases ranged from 0.4 (4°C) to 2.2 (25°C) log CFU/3.1 cm2. Maximum populations occurred at 25°C at 7 days (5.3 log CFU/3.1 cm2).

Significance: Food safety risks associated with contamination of whole melons vary depending on pathogen, melon, and postharvest handling.  Salmonella did not increase on either watermelon or cantaloupe; E. coli O157:H7 did not increase on watermelon, but did increase above 15°C on cantaloupe; L. monocytogenes increased on watermelon above 20°C and at all temperatures on cantaloupe.