Survival and Persistence of Nonpathogenic Escherichia coli and Attenuated Escherichia coli O157:H7 in Soils Amended with Animal Manure in a Greenhouse Environment

Abstract

Animal manure provides benefits to agriculture but may contain pathogens that contaminate ready-to-eat produce. U.S. Department of Agriculture National Organic Program standards include 90- or 120-day intervals between application of manure and harvest of crop to minimize risks of pathogen contamination of fresh produce. Data on factors affecting survival of Escherichia coli in soils under greenhouse conditions are needed. Three separate studies were conducted to evaluate survival of nonpathogenic E. coli (gEc) and attenuated E. coli O157:H7 (attO157) inoculated at either low (4 log CFU/ml) or high (6 log CFU/ml) populations over 56 days. Studies involved two pot sizes (small, 398 cm(3); large, 89 liters), three soil types (sandy loam, SL; clay loam, CL; silt loam, SIL), and four amendments (poultry litter, PL; dairy manure liquids, DML; horse manure, HM; unamended). Amendments were applied to the surface of the soil in either small or large containers. Study 1, conducted in regularly irrigated small containers, showed that populations of gEc and attO157 (2.84 to 2.88 log CFU/g) in PL-amended soils were significantly (P < 0.05) greater than those in DML-amended (0.29 to 0.32 log CFU/g [dry weight] [gdw]) or unamended (0.25 to 0.28 log CFU/gdw) soils; soil type did not affect E. coli survival. Results from study 2, in large pots with CL and SIL, showed that PL-amended soils supported significantly higher attO157 and gEc populations compared with HM-amended or unamended soils. Study 3 compared results from small and large containers that received high inoculum simultaneously. Overall, in both small and large containers, PLamended soils supported higher gEc and attO157 populations compared with HM-amended and unamended soils. Populations of attO157 were significantly greater in small containers (1.83 log CFU/gdw) than in large containers (0.65 log CFU/gdw) at week 8, perhaps because small containers received more regular irrigation than large pots. Regular irrigation of small pots may have affected E. coli persistence in manure-amended soils. Overall, PL-amended soils in both small and large containers supported E. coli survival at higher populations compared with DML-, HM-, or unamended soils.

Microbiological quality of spinach irrigated with reclaimed wastewater and roof-harvest water

“…; Sharma et al . ). The persistence of E. coli on leafy green commodities also varies depending on the nutrient availability, competition with indigenous microflora and relative humidity (Erickson et al .…”

“…Higher organic matters present in the water may increase the persistence of these bacteria on fresh produce. Furthermore, bacterial attachment to produce surfaces varies with natural bacteria isolated from different environmental sources (Ilic et al 2008; Patel et al 2010;Sharma et al 2016). The persistence of E. coli on leafy green commodities also varies depending on the nutrient availability, competition with indigenous microflora and relative humidity (Erickson et al 2010).…”

Composts of poultry litter or dairy manure differentially affect survival of enteric bacteria in fields with spinach

“…Greater survival of these E. coli strains in soils amended with poultry litter than dairy manure‐based soil amendments was observed previously in a greenhouse setting (Sharma et al . ) and in field trials conducted in the Mid‐Atlantic United States (Sharma et al . ).…”

“…; Sharma et al . ). Each E. coli strain was grown in tryptic soy broth with 80 μ g ml −1 rifampicin (TSBR) and adjusted to a final population of 1·67 × 10 5 CFU per ml.…”

“…The overall aim of this study was to determine survival and persistence of E. coli populations in a field experiment comparing composts from manure sources that demonstrated varying levels of E. coli survival in a prior greenhouse pot experiment (Sharma et al . ). A cocktail of three nonpathogenic E. coli isolates were surrogates for food‐borne pathogens.…”