title: Influence of mycorrhizal fungi on fate of E. coli O157:H7 and Salmonella in soil and internalization into Romaine lettuce plants.
abstract: The objectives of this study were to determine the influence of a symbiotic arbuscular mycorrhizal (AM) fungus on persistence of Salmonella and enterohemorrhagic Escherichia coli O157:H7 (EHEC) within soil, and survival within Romaine lettuce. Romaine seedlings were grown with or without AM fungi. Soil surrounding plants was inoculated with ca. 8 log CFU/plant of either Salmonella enterica or E. coli EHEC composites. Samples (soil, root, and shoot) were analyzed on days 1, 8, 15 and 22 for Salmonella and EHEC by direct plating and selective enrichment. Twenty-four hours after inoculation, populations of Salmonella and EHEC, respectively, were 4.20 and 3.24 log CFU/root, 2.52 and 1.17 log CFU/shoot, and 5.46 and 5.17 log CFU/g soil. By selective enrichment, samples tested positive for Salmonella or EHEC at day 22 at rates of 94 and 68% (shoot), 97 and 56% (root), and 100 and 75% (soil), respectively, suggesting that Salmonella has a greater propensity for survival than EHEC. Salmonella populations in soil remained as high as 4.35 log CFU/g by day 22, while EHEC populations dropped to 1.12 log CFU/g in the same amount of time. Ninety-two percent of all Romaine leaves in our study were positive for internalized Salmonella from days 8 to 22 and remained as high as 1.26 log CFU/shoot on day 22 in AM fungi+Romaine plants. There were no differences (P>0.05) between the survival of either pathogen based on the presence or absence of mycorrhizal fungi. Results of this study suggest that AM fungi do not affect the internalization and/or survival of either S. enterica or E. coli O157:H7 in Romaine lettuce seedlings. Our results should provide Romaine lettuce farmers confidence that the presence and/or application of AM fungi to crop soil is not a contributing factor to the internalization and survival of Salmonella or E. coli O157:H7 within Romaine lettuce plants.
authors.affiliation: College of Agriculture and Related Sciences, Delaware State University, 1200 N DuPont Hwy, Dover Delaware 19901, United States.
authors.forename: April M
authors.initials: AM
authors.lastname: Nicholson
authors.affiliation: Food Safety Intervention Technologies Research Unit, U.S., Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038-8551, United States. Electronic address: joshua.gurtler@ars.usda.gov.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Gurtler
authors.affiliation: Food Safety Intervention Technologies Research Unit, U.S., Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038-8551, United States.
authors.forename: Rebecca B
authors.initials: RB
authors.lastname: Bailey
authors.affiliation: Food Safety Intervention Technologies Research Unit, U.S., Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038-8551, United States.
authors.forename: Brendan A
authors.initials: BA
authors.lastname: Niemira
authors.affiliation: Molecular Characterization and Foodborne Pathogen Research Unit, U.S., Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038-8551, United States.
authors.forename: David D
authors.initials: DD
authors.lastname: Douds
mesh_terms: D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000502:physiology*; D005516:Food Microbiology; D005658:Fungi / Q000502:physiology; D055137:Glomeromycota / Q000502:physiology*; D018545:Lactuca / Q000382:microbiology*; D038821:Mycorrhizae / Q000502:physiology; D018515:Plant Leaves / Q000382:microbiology; D018517:Plant Roots / Q000382:microbiology; D012475:Salmonella / Q000502:physiology*; D036226:Seedlings / Q000382:microbiology; D012988:Soil Microbiology
keywords: Arbuscular mycorrhizal fungi; E. coli O157:H7; Romaine lettuce; Salmonella