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ARS Home » Northeast Area » Wyndmoor, Pennsylvania » Eastern Regional Research Center » Food Safety and Intervention Technologies Research » Research » Publications at this Location » Publication #285379
Title: Influence of mycorrhizal fungi on fate of E. coli 0157:H7 in soil and Salmonella in soil and internalization into romaine lettuce plants

Author
item NICHOLOSON, APRIL - Delaware State University
item Gurtler, Joshua
item Bailey, Rebecca
item Niemira, Brendan
item Douds, David

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2014
Publication Date: 1/10/2015
Citation: Nicholoson, A.M., Gurtler, J., Bailey, R., Niemira, B.A., Douds, D.D. 2015. Influence of mycorrhizal fungi on fate of E. coli 0157:H7 in soil and Salmonella in soil and internalization into romaine lettuce plants. International Journal of Food Microbiology. 192:95-102.

Interpretive Summary: The objectives of this study were to determine the influence of arbuscular mycorrhizal (AM) fungi on Salmonella and enterohemorrhagic E. coli O157:H7 (EHEC) within soil, and their survival within Romaine lettuce. Romaine seedlings were grown with or without AM fungi. Soil surrounding plants was inoculated with either Salmonella or EHEC and samples were tested up to 22 days. Salmonella or EHEC, respectively, were detected in 94 and 68 percent of Romaine leaf samples, in 97 and 56 percent of Romaine root samples, and in 100 and 75 percent of soil samples. Thus, Salmonella survived much better than EHEC. Salmonella populations in soil remained as high as 22,400 bacteria per gram by day 22, while EHEC populations dropped to only 13 bacteria per gram in the same amount of time. Ninety-two percent of all Romaine leaves in our study were positive for internalized Salmonella from days 8-22. There were no differences (P is greater than 0.05) between the survival of either pathogen based on the presence or absence of mycorrhizal fungi. These results suggest that the presence of AM fungi does not affect the internalization and/or survival of either enterica or EHEC in Romaine lettuce seedlings. Our results should also 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.

Technical Abstract: The objectives of this study were to determine the influence of arbuscular mycorrhizal (AM) fungi on persistence of Salmonella and enterohemorrhagic E. coli O157:H7 (EHEC) within soil, and survival within Romaine lettuce. Romaine seedlings were grown with or without AM fungi, i.e., soil fungi that form a mutualistic symbiosis with roots of the majority of plants. 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 that tested positive for Salmonella or EHEC, respectively, through day 22 were 94 and 68 percent (shoot), 97 and 56 percent (root), and 100 and 75 percent (soil), suggesting a greater propensity for Salmonella survival. 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 8-22 and remained as high as 1.26 log CFU/shoot on day 22 in AM fungi+ Romaine plants. There were no differences (P is greater than 0.05) between the survival of either pathogen based on the presence or absence of mycorrhizal fungi. Results of this study suggest that the presence of AM fungi does not affect the internalization and/or survival of either Salmonella enterica or E. coli O157:H7 in Romaine lettuce seedlings. Our results should also 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.