P1-168 Influence of Plant Pathogenic and Commensal Bacteria on the Uptake of Escherichia coli and Listeria innocua in Salad Vegetable Plants

Sunday, July 26, 2015
Exhibit Hall (Oregon Convention Center)
Hudaa Neetoo , Un , Newark , DE
Keshavi Ghoorbin
Kirtee Benee
Seelavarn Ganeshan
Introduction: Produce-related outbreaks continue to be on the rise. Escherichia coli O157:H7 and Listeria monocytogenes are important zoonotic or geonotic pathogens often associated with fresh produce. Although uptake of these human pathogens into vegetable plants has been extensively investigated, the potential role of plant microbiota on internalization has garnered less attention.

Purpose: The study aimed to investigate the potential transfer of Escherichia coli ATCC 25922 and Listeria innocua ATCC 33090, surrogate microorganisms for E. coli O157:H7 and L. monocytogenes, respectively, from artificially contaminated soil into the edible portion of vegetables, as affected by the presence of phytopathogen Ralstonia solanacearum or plant commensal Pseudomonas fluorescens.

Methods: Tomatoes, bell peppers and green onions were cultivated in sterile soil (aw ~ 0.98, pH ~ 7.45) in a greenhouse for approximately 60 days. Each potted vegetable was soil-inoculated with a suspension (ca. 108 CFU/ml) of nalidixic-acid resistant E. coli (EC) or L. innocua (LI). In addition, selected vegetables were co-inoculated with R. solanacearum (RS) or P. fluorescens (PF) on alternate days. A total of six inoculation treatments were considered: EC, EC+PF, EC+RS, LI, LI+PF and LI+RS. Mature tomatoes (110), peppers (86) and green onions (63) were harvested and analyzed by traditional culturing methods using selective media supplemented with 50 µg/ml of nalidixic acid.

Results: EC and LI were undetectable in tomato and pepper fruits analyzed by both plating (< 1.7 - 2.2 log CFU/g) and enrichment methods. EC and LI were isolated from the foliar parts of green onions at a maximum population density of 3.4 and 3.7 log CFU/g, respectively. Uptake of these microorganisms in green onions was not significantly affected by the presence of RS or PF (P > 0.05). 

Significance: Findings point to the possible transference of zoonotic or geonotic pathogens from soil into onion plants and the health risks associated with the consumption of raw green onions.