Purpose: To obtain environmental surveillance data on the incidence and prevalence of L. monocytogenes on stone and pome fruits in pre-harvest and post-harvest fruit production environments.
Methods: Stone fruit collection in the orchards and environmental sampling at the Penn State Fruit Research and Extension Center stone fruit packing and storage facility was conducted during 2014 and 2015 seasons. L. monocytogenes detection and identification was conducted following BAM protocols. Whole genome sequencing of 6 L. monocytogenes isolates was completed via Illumina platform. Multi locus sequence (MLST) and core genome MLST analyses were performed to compare these isolates with other fully sequenced L. monocytogenes strains.
Results: Overall, 15.3 % (n = 216) of the postharvest environmental samples were positive for Listeria; however, no L. monocytogenes was found in the fruit packing and storage facility. The incidence of the L. monocytogenes on intact stone fruits in the orchards was 1.1% (n = 540). MLST analysis identified 3 isolates belonging to sequence type (ST) 368 and 3 other belonging to a novel ST. Core genome MLST identified the isolates with ST368 closely related to a strain from natural environment (sidewalk) with 12 allele differences. The isolates with the novel ST were not closely related to any of the fully sequenced strains and the closest match was a strain from an animal source with 556 allele differences.
Significance: Identification of the biological and environmental factors leading to stone fruit contamination by L. monocytogenes will facilitate the development of preventive control strategies to significantly reduce the number of recalls and foodborne listeriosis associated with consumption of stone fruits.