Biological soil amendments can support survival of pathogenic and non-pathogenic Escherichia coli in soils and sporadic transfer to Romaine lettuce

Abstract

Biological soil amendments (BSAs) are essential agricultural inputs that provide critical nutrients in organic leafy green production. Heat-treated poultry pellets (HTPP) and seabird guano (SBG), which have been treated to reduce microbial pathogen loads, are gaining popularity among growers. Using these BSAs in the process of side-dressing, providing nutrients to crops while growing, may provide opportunities for externally introduced bacterial pathogens to survive in soil. In this study, Romaine lettuce was grown in soils in a controlled environmental growth chamber. Soils were side-dressed twice with different combinations of treated BSAs: HTPP, SBG, and corn steep liquor (CSL). Soils were co-inoculated with non-pathogenic E. coli and two E. coli O157:H7 strains at the second of two side-dressing events. Survival of E. coli in soils over 28 days was evaluated. On day 28 post inoculation, two heads of Romaine lettuce from each planter were harvested, and the presence of E. coli on leaves was determined. Four nonlinear statistical models were fit to predict survival of E. coli in soils. In all soils regardless of BSA treatment, E. coli TVS 353 declined by 4.08–4.51 log CFU/g soil over 28 days, and E. coli O157:H7 declined by 2.77–4.3 log CFU/g soil over 28 days. E. coli TVS 353 and O157:H7 were recovered from 13.3 % (6/45) and 11.1 % (5/45) of plants, respectively. Transfer of E. coli from soils to Romaine lettuce was low, sporadic, and could not be measured quantitatively. Side-dressing with treated BSAs used in organic lettuce production supported but did not enhance survival of E. coli in side-dressed soils under controlled environmental conditions.