ARS | Publication request: Influence of mycorrhizal fungi on survival of salmonella and E.coli O157:H7 in soil and translocation into allium porrum roots and stem

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 2, 2011
Publication Date: August 2, 2011
Citation: Gurtler, J., Douds, D.D., Dirks, B.P., Quinlan, J.J., Niemira, B.A. 2011. Influence of mycorrhizal fungi on survival of salmonella and E.coli O157:H7 in soil and translocation into allium porrum roots and stem. International Association for Food Protection Annual Meeting, Milwaukee, Wisconsin, July 31 - August 3, 2011., Volume 1, P. 1.

Technical Abstract: Modern agriculture disrupts the natural symbiotic relationship arbuscular mycorrhizal (AM) fungi have with most vegetable plants, which may affect translocation of human pathogens into the plant. Five-month-old Allium porrum (leek) plants (with or without AMF [Glomus intraradices]) were used as a model. Plants were inoculated (8 ml per plant) with composite suspensions of either nalidixic acid resistant Salmonella or EHEC at a low level (5 log CFU/ml) or a high level (8 log). Samples were taken one day following inoculation as well as weekly up to 1 and 3 weeks for low and high inocula, respectively. Samples were plated on XLT4PN and tcSMACPN, respectively. Pre-enrichments were made in TSBPN, while secondary enrichments were in TTPN for Salmonella and a novel TSBselect broth for EHEC. Both pathogens at the high inoculum level were detected at higher levels in AMF+ roots and shoots versus non-AMF roots through the three week sampling. Pathogens were ca. 0.5 log CFU/g higher in the AMF-free soil versus AMF+ soil at week 3, suggesting possible AMF-mediated suppression. Pathogens at the low inoculum level were detected by direct plating on day one, but only by enrichment for non-AMF Salmonella-inoculated roots at one week. Both pathogens in the soil at the low inoculum level were ca. 4.4 log CFU/g on day one; however, at the one week sampling time, Salmonella levels were 3 log CFU/g, while EHEC levels were 2.2 log CFU/g, with or without AMF. All negative controls tested negative for pathogens. These results indicate that Allium porrum can be colonized in the root and shoot when soil is inoculated with either Salmonella or E. coli O157:H7. Symbiotic AMF may reduce survival of human pathogens in the soil.