Survival and growth of Listeria monocytogenes on fresh-cut ‘Athena’ and ‘Rocky Ford’ cantaloupes during storage at 4 and 10°C

Authors: NYARKO, ESMOND - University Of Delaware; KNIEL, KALMIE - University Of Delaware; REYNNELLS, RUSSELL - University Of Maryland Eastern Shore (UMES); East, Cheryl - Roberts; Handy, Eric; Luo, Yaguang - Sunny; Millner, Patricia; Sharma, Manan

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2016
Publication Date: 11/1/2016
Citation: Nyarko, E., Kniel, K., Reynnells, R., East, C.L., Handy, E.T., Luo, Y., Millner, P.D., Sharma, M. 2016. Survival and growth of Listeria monocytogenes on fresh-cut ‘Athena’ and ‘Rocky Ford’ cantaloupes during storage at 4 and 10°C. Foodborne Pathogens and Disease. 13:587-591.

Interpretive Summary: Listeria monocytogenes is a bacterial foodborne pathogen that has been associated with a number of food commodities (deli meats, soft cheeses, and cantaloupes). In 2011, one of the deadliest outbreaks in U.S. history occurred when individuals consumed ‘Rocky Ford’ cantaloupes contaminated with L. monocytogenes resulted in 147 cases of infection and 33 deaths. The pathogen can be transferred from the rind of the melon to the flesh through cutting and therefore, it is important to understand if L. monocytogenes can grow on fresh-cut cantaloupes stored at different temperatures. We inoculated fresh-cut cantaloupes with L. monocytogenes and stored them at 4oC for 15 days or 10oC for 7 days. Our results show that L. monocytogenes on fresh-cut cantaloupes grew more rapidly at 10oC than at 4oC. Our results also showed that holding fresh-cut cantaloupes at 25oC for 4 h immediately after cutting did not allow the L. monocytogenes populations to grow to higher populations compared to those stored continuously at 4oC. However, fresh-cut cantaloupes which were refrigerated at 4oC for 24 h, temperature-abused 24 h later, and then stored at 4oC for another 48 h did show significantly higher populations of L. monocytogenes compared to those stored continuously at 4oC for 72 h. This does indicate that some types of temperature abuse can encourage the growth of the pathogen on fresh cut cantaloupes. Overall, these results show that the growth of L. monocytogenes on fresh cut cantaloupes can occur during refrigerated storage, but is enhanced at abusive storage temperatures (10oC) and by temperature-abuse events which interrupt refrigerated storage. This information will be useful to other scientists, the produce industry and regulatory agencies.

Technical Abstract: Cantaloupes, marketed as ‘Rocky Ford’, were implicated in the fatal U.S. multi-state outbreak of listeriosis in 2011. Listeria monocytogenes can survive on whole cantaloupes and can be transferred to the flesh of melons. The growth of L. monocytogenes on fresh-cut ‘Athena’ and ‘Rocky Ford’ cantaloupe cultivars during refrigerated storage was evaluated. Fresh-cut cubes (1-in3) from field-grown cantaloupes were each inoculated with 5 log CFU/mL of a multi-strain inoculum of L. monocytogenes and stored at 4oC or 10oC. Inoculated fresh-cut cubes were also: (1) continuously stored at 4oC for 3 days; (2) temperature-abused (TA; 25oC for 4 h) on day 0; or (3) stored at 4oC for 24 h, exposed to TA on day 1, and subsequently stored at 4oC until day 3. L. monocytogenes populations on fresh-cut melons continuously stored at 4°C or 10°C were enumerated on selected days for up to 15 days, and after each TA event. Brix values for each cantaloupe variety were determined. L. monocytogenes populations on fresh-cut cantaloupes stored at 4oC increased by 1.0 and 3.0 log CFU/cube by day 7 and 15, respectively, whereas those stored at 10oC increased by 3.0 log CFU/cube by day 7. Populations of L. monocytogenes on fresh-cut cantaloupes stored at 10oC were significantly (P<0.05) greater than those stored at 4oC during the study. Growth of L. monocytogenes on fresh-cut ‘Athena’ and ‘Rocky Ford’ cantaloupes was similar, even though ‘Athena’ had significantly higher Brix values than ‘Rocky Ford’ cantaloupes. On day 3, L. monocytogenes populations on fresh-cut cantaloupes exposed to TA on day 1 and then refrigerated were significantly greater (0.74 log CFU) than those stored continuously at 4oC. Fresh-cut cubes of cantaloupes stored at 10°C or exposed to temperature-abuse events promoted growth of L. monocytogenes on fresh-cut cantaloupes during refrigerated storage.