Listeria monocytogenes in tree fruits; the prevalence and potential mechanisms of contamination

Listeria monocytogenes is estimated to cause over 1,600 illnesses and 250 deaths annually in the United States, making it one of the leading causes of death from bacterial foodborne diseases. Most listeriosis outbreaks have historically been linked to ready-to-eat meats and dairy products; however, fresh produce-associated listeriosis outbreaks are increasingly recognized. Whether the emergence of produce as a vehicle for listeriosis represents a true increase in produce-associated illnesses or just an improvement in outbreak detection is unclear. The 2014-2015 multistate listeriosis outbreak associated with contaminated caramel apples, the 2014 recall of stone fruits due to L. monocytogenes contamination, the 2014-2015 Food and Drug Administration surveillance findings of L. monocytogenes in whole fresh avocados serve as a reminder that the historical absence of outbreaks linked to a particular low-risk product does not imply an absence of risk. Contamination of tree fruits remains a complex issue because many of the conditions that promote the contamination and persistence of this pathogen in the environment and in planta are not known. A better understanding of the ecology, distribution and survival of L. monocytogenes in the tree fruit production continuum is paramount to developing efficient prevention and control strategies. This lecture will highlight latest findings on the L. monocytogenes prevalence of the tree fruit production environments as well as present research on identification of high-risk postharvest practices, potentially facilitating contamination and survival of L. monocytogenes in tree fruits.