Purpose: To determine the influence of AM-fungi (AMF) on survival of Salmonella and E. coli O157:H7 (EHEC) in soil and translocation into plant roots and shoot.
Methods: Six-week-old Romaine lettuce plants (with or without AMF [Glomus intraradices]) were inoculated (8 ml per plant) with composite suspensions of Salmonella or EHEC (8 log CFU/plant). Samples were taken one day following inoculation and then weekly up to 22 days. 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.
Results: Salmonella and EHEC both internalized Romaine roots and shoots for up to 22 days following inoculation. Overall, there was little difference in pathogen populations between AMF+ and AMF- roots, shoots, and soil. This is in contrast to results attained from previous studies using a leek model. Salmonella populations were higher than EHEC P < 0.05) for 63% of all root and shoot samples; while final populations of the two pathogens in the soil at day 22 were ca. 4.3 and 1.2 log CFU/g, respectively. Selective enrichment samples (96%) for plant tissue were positive for Salmonella on day 22, while only 29% of EHEC enrichments were positive. Soil samples (100%) were positive for Salmonella by selective enrichment, and 83% were positive for EHEC by day 22.
Significance: These results are the first to suggest that AM-fungi do not influence the internalization of pathogens in Romaine seedlings, which may provide some assurance of the safe application of AMF in modern agricultural practices.