|NAYARKO, ESMOND - University Of Delaware|
|KNIEL, KALMIA - University Of Delaware|
|Luo, Yaguang - Sunny|
|REYNNELLS, RUSSELL - University Of Maryland Eastern Shore (UMES)|
|East, Cheryl - Roberts|
Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2016
Publication Date: 10/3/2016
Publication URL: http://handle.nal.usda.gov/10113/63062
Citation: Nayarko, E., Kniel, K., Millner, P.D., Luo, Y., Handy, E.T., Reynnells, R., East, C.L., Sharma, M. 2016. Survival and growth of Listeria monocytogenes on whole cantaloupes is dependent on site of contamination and storage temperature. International Journal of Food Microbiology. 234:65-70.
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, which resulted in 29 deaths and 147 hospitalizations. Our research here examined the survival of L. monocytogenes on different varieties (‘Rocky Ford’ and ‘Athena) of cantaloupes stored at different temperatures to determine which factors influence L. monocytogenes on cantaloupe surfaces. Our work found that when cantaloupes were stored at 25oC , L. monocytogenes can grow on the ‘stem scar’ area (where the vine of the plant attaches to the melon). Similarly, at lower storage temperature (4 and 10oC), L. monocytogenes populations remained viable on the stem scar. In contrast, populations of L. monocytogenes did not survive well on the cantaloupe rinds, declining at all three storage temperatures evaluated. We also did not find differences in survival of L. monocytogenes on Rocky Ford and Athena cantaloupes. In conclusion, the specific site of cantaloupe contamination and storage temperature influences the growth and survival of L. monocytogenes, regardless of the cultivar evaluated. This information should be useful to other scientists, regulatory agencies and the produce industry.
Technical Abstract: Whole cantaloupes (Cucumis melo L), marketed as ‘Rocky Ford’, were implicated in a large multi-state outbreak of listeriosis in the United States in 2011; however, survival and growth of Listeria monocytogenes on whole cantaloupes remains relatively unexplored. The research presented here evaluated three different storage temperatures, two sites of contamination of cantaloupes, and two cantaloupe varieties to determine their effect on the survival of L. monocytogenes. ‘Athena’ and ‘Rocky Ford’ cantaloupe cultivars were grown in soil, harvested, and individual melons subsequently received a multi-strain inoculum of L. monocytogenes (ca. 6 log CFU/melon), which were then stored at 4°C, 10°C, and 25°C. Changes in populations of L. monocytogenes on the rinds and stem scars of cantaloupes stored at each temperature were determined at selected times for up to 15 days. An analysis of variance revealed that inoculation site and storage temperature significantly (P<0.05) affected populations of L. monocytogenes on cantaloupes during storage, but cultivar did not influence (P>0.05) populations. Populations of L. monocytogenes on stem scars of cantaloupes stored at 25oC increased by 1 – 2 log CFU/melon on day 1, and were significantly greater (P<0.05) than those on cantaloupes stored at 4oC or 10°C, which remained constant or increased by approximately 0.3 log CFU/melon, respectively, over the same time period. A decrease of 2–5 log CFU/melon in populations of L. monocytogenes occurred on the rinds of cantaloupes during storage by day 7, and were not significantly (P>0.05) different at the three different storage temperatures. In trials performed in rind juice extracts, populations of L. monocytogenes decreased by 3 log CFU/mL when stored at 25°C by day 3, but populations grew by 3 – 4 log CFU/mL when stored at 4°C over 7 days. Overall, site of contamination and storage temperature influenced the survival of L. monocytogenes on cantaloupes more than cantaloupe cultivar type.