Purpose: The objective of the study was to assess survival and growth of outbreak strains of L. monocytogenes on the outer surface of cantaloupe (rind) compared to inner surface (flesh) or in freshly extracted juice at various incubation temperatures.
Methods: Three L. monocytogenes strains implicated in the 2011 multistate outbreak in cantaloupe were employed in this study. Two strains were of serotype 1/2a and the third of serotype 1/2b. Cantaloupe was obtained at retail. Pre-wetted, freshly cut pieces of cantaloupe rind and flesh as well as cantaloupe extract were inoculated with L. monocytogenes (105 CFU /fragment or ml). Survival and growth were assessed by enumeration of cells over 21 days of incubation at 4 and 8°C and seven days of incubation at 25°C. Data were statistically analyzed with SAS using the linear mixed effects model
Results: L. monocytogenes populations increased by approximately 10 fold following 21 days incubation at 4 or 8°C, and by approximately 100 fold following 7 days incubation at 25°C. After 24 hours at 25°C L. monocytogenes populations increased by approximately 10 fold. Interestingly, increases were higher on the rind than on the flesh or in the juice, with statistically significant differences (P < 0.0001) after 7 days of incubation at 4°C and 72 h at 25°C. No significant differences were noted among the three different strains
Significance: The results of this study suggest that L. monocytogenes can not only survive on the surface of cantaloupe but that it also has temperature and time-dependent potential for growth. The data will be valuable in design of controls to limit persistence and growth of this pathogen on cantaloupe and other produce.