Purpose: To investigate 1) survival of non-pathogenic Escherichia coli (Ec) and attenuated E. coli O157:H7 (attO157) in soils amended with poultry litter (PL) or horse manure (HM) from fall/winter 2013/2014.
Methods: Field plots (Othello soil) were amended with PL or HM. An inoculum containing equal numbers of three and two rifampicin-resistant (RifR) strains of Ec and attO157-RifR strains, respectively was sprayed onto soils at low 6.73 x 106 CFU/m2 (LC) or high 7.2 x 108 CFU/m2 (HC) concentrations, and manure was either surface-applied or tilled into soil. Soil samples were collected between 0-91 days post-inoculation (dpi), and Ec and attO157 populations were determined by direct plating and/or mini-MPN.
Results: Populations declined more rapidly in unamended soil than in soils amended with HM and PL. In unamended soil at HC, Ec concentrations declined by 2.1 and 2.4 log CFU/g in surface and core samples 91 dpi, respectively. When Ec was applied at LC, populations in surface and core samples declined by 2.73 and 1.39 log CFU/g, respectively, over 91 dpi, in unamended soils. A similar trend was observed in soils amended with HM and PL. At 7 dpi, populations of EC and attO157 in LC in surface-applied unamended, PL and HM soils increased by > 1 log CFU/g, corresponding to rain events over the same period. Generally, E. coli populations persisted longer in soils amended with PL than with HM and were greater in surface than in core samples.
Significance: Manure type, method of application, and winter environmental factors influenced survival of E. coli in soil. Both Ec and attO157 survived longer in manure-amended soils compared to unamended soils, indicating the effect manure has in extending survival of bacteria in soils.