Purpose: To investigate 1) survival and persistence of non-pathogenic Escherichia coli (Ec) and attenuated E. coli O157:H7 (attO157) before and 24h after irrigation events in silt loam soil (SL) unamended (UN), amended with poultry litter (PL) or horse manure (HM) and 2) to compare survival of Ec and attO157 in manure-amended SL and clay loam soil (CL).
Methods: Twenty-four large pots (2552.5 cm3), half containing either SL or CL in a greenhouse, were amended with PL, HM, or UN (n = 4 per treatment). All soils were sprayed with 7.2 x 108 CFU/m2 of an inocula containing three Ec and two attO157 strains, all rifampicin-resistant. SL treatments were sampled on days 6, 13, 27 and 55 post-inoculation (dpi), and then both SL and CL treatments were irrigated. All samples were collected 24h after each irrigation. E. coli populations were determined by direct plating and/or mini-MPN.
Results: Populations of Ec increased by 3.11, 1.07, and 1.20 log CFU/g on days 14, 28, and 56, respectively, while attO157 populations increased by 3.2, 0.97 and 0.48 log CFU/g on these same days, after irrigation of PL-amended SL. E. coli populations in UN-SL increased by 0.84 log CFU/g after irrigation on day 28, but decreased 0.15 log CFU/g after irrigation on day 56. Overall, all E. coli populations declined more rapidly in unamended and HM-amended SL and CL than in these same soils amended with PL.
Significance: The resuscitation of E. coli cells was enhanced by irrigation of PL-SL even 56 dpi, in contrast to UN and HM amendment. Consideration of these findings will contribute to development of guidelines for produce safety relative to PL and other soil amendments.