Pathogens, Indicators and Antibiotic Resistance Genes in Soils with Land Applied Poultry Litter

Introduction: Poultry litter (PL) is a by-product of broiler production most of which is land applied where it is a valuable nutrient source for crop production. PL can also be a route of contamination with manure-borne bacteria; in fact, two of the top causes of foodborne illness, Campylobacter sp. and Salmonella sp. are found in association with poultry and poultry litters.

Purpose: This two year field study was conducted to determine the fate of naturally occurring pathogens, fecal indicator bacteria (FIB) and bacteria containing antibiotic resistance genes (ARG) following application of PL to soils under conventional till (CT) or no (NT) till management.

Methods: Microbial populations were quantified in soils with applied PL using a combination of culture and quantitative, real-time (qPCR) analysis.

Results: Initial concentrations of Campylobacter jejuni (C. jejuni) in PL were 5.4 ± 3.2 X 10⁶ cells per gram PL; Salmonella sp. was not detected in the PL, but was enriched periodically from PL amended soils (particularly CT soils). Escherichia coli (E. coli) was detected in PL (1.5 ± 1.3 X 10² culturable or 1.5 ± 0.3 X 10⁷ genes per gram) but was rarely detected in field soils while enterococci (1.5 ± 0.5 X 10⁸ cells per gram PL) were detected throughout the study. Within one or two days of PL application, concentrations of ARG for sulfonamide and tetracycline resistance increased orders of magnitude above background and remained elevated for the duration of the study.

Significance: These results suggest that enterococci may be better FIB for field applied PL and show that application rates (including bacterial load and nutrients) and re-application had more influence on microbial populations than did CT or NT management of soils. These data provide new knowledge about survival of important FIB, pathogens, and ARG associated with PL applied under realistic field-based conditions.