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T7-06 Persistence and Transmission of Escherichia coli and Salmonella spp. in a Watermelon Field Ammended with Poultry Litter:  Year Two

Tuesday, July 11, 2017: 2:45 PM
Room 15 (Tampa Convention Center)
Thais De Melo Ramos , University of Delaware , Newark , DE
Shani Craighead , University of Delaware , Newark , DE
Patrick Spanninger , University of Delaware , Newark , DE
Claire Marik , University of Delaware , Newark , DE
Samantha Gartley , University of Delaware , Newark , DE
Adam Vanore , University of Delaware , Newark , DE
Gordon Johnson , University of Delaware , Newark , DE
Manan Sharma , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Kalmia Kniel , University of Delaware , Newark , DE
Introduction: Poultry litter (PL) is a nutrient-rich soil amendment for crop production. However, the use of PL in soils may introduce enteric pathogens to fruits and vegetables.

Purpose:  This study evaluated the persistence of a nonpathogenic, rifampicin-resistant Escherichia coli strain (TVS 355) and the presence of naturally occurring Salmonella spp. in soil, soil amended with PL, and on field-grown watermelons.

Methods: From May to October, 2016, twelve individual plots were seeded with Exclamation and Liberty watermelons planted on plastic mulch. Plots were unamended, unamended and inoculated with E. coli, amended with PL, or amended with E. coli inoculated PL. Soil samples were collected weekly (n=348). Watermelons (n=108) were swabbed at harvest. Samples were analyzed for E. coli populations by direct plating or MPN, and for Salmonella spp. by MPN using RV and TT broth or by enrichment using a modified FDA BAM procedure.

Results:   By day eight, E. coli levels were significantly (P<0.0001) greater in PL-amended soils (5.02 log CFU/ gdw (gram dry weight) compared to unamended soils (3.98 log CFU/gdw). By day 120, E. coli populations in PL-amended soils were significantly (P<0.0001) greater (1.15±0.66 log CFU/gdw) compared to those in unamended plots which were below (0.12±0.01 log CFU/gdw). Salmonella spp. were detected in 62% of soil samples. By day eight the mean Salmonella spp. populations recovered from PL-amended and unamended plots were 1.36±0.40 log MPN/gdw and 1.08±0.27 log MPN/gdw, respectively. After 120 days, Salmonella spp. counts were 1.21±0.57 log MPN/gdw from PL-amended and 1.69±0.72 log MPN/gdw from unamended plots. Salmonella spp. were detected on watermelons (28 of 108) grown in both amended and unamended soils, containing E. coli populations that ranged from 1.95 to 2.81 log MPN/gdw. Approximately 92% of watermelons swabbed were positive for E.coli.

Significance: PL-amended soils provided conducive environments for E. coli persistence throughout the growing season and facilitated transfer to watermelons.

Back to: Technical Session 7 - Pre-harvest Food Safety and Water
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