Modeling the growth of Listeria monocytogenes on cut cantaloupe, honeydew and watermelon

• A model describing the growth kinetics of Listeria monocytogenes on cut melons is described.
• Faster growth of L. monocytogenes than of Salmonella or Escherichia coli O157:H7 is predicted below 20 °C.
• The model agrees with estimates from ComBase and a corrected published model for L. monocytogenes on cantaloupe.
• A 4 log CFU increase after 15 days at 5 °C and a 1 log CFU increase following 6 days at 4 °C are predicted.

A recent outbreak linked to whole cantaloupes underscores the importance of understanding growth kinetics of Listeria monocytogenes in cut melons at different temperatures. Whole cantaloupe, watermelon, and honeydew purchased from a local supermarket were cut into 10 ± 1 g cubes. A four-strain cocktail of L. monocytogenes from food related outbreaks was used to inoculate fruit, resulting in ∼103 CFU/10 g. Samples were stored at 4, 10, 15, 20, or 25 °C and L. monocytogenes were enumerated at appropriate time intervals. The square root model was used to describe L. monocytogenes growth rate as a function of temperature. The model was compared to prior models for Salmonella and Escherichia coli O157:H7 growth on cut melon, as well as models for L. monocytogenes on cantaloupe and L. monocytogenes ComBase models. The current model predicts faster growth of L. monocytogenes vs. Salmonella and E. coli O157:H7 at temperatures below 20 °C, and agrees with estimates from ComBase Predictor, and a corrected published model for L. monocytogenes on cut cantaloupe. The model predicts ∼4 log CFU increase following 15 days at 5 °C, and ∼1 log CFU increase following 6 days at 4 °C. The model can also be used in subsequent quantitative microbial risk assessments.