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Decay Of Bacterial Pathogen, Fecal Indicators, And Real-Time Quantitative PCR Genetic Markers In Manure Amended Soils
Citation:
Rogers, S. W., M. Donnelly, L. Peed, C. A. KELTY, S. Mondal, Z. Zhang, AND O. C. SHANKS. Decay Of Bacterial Pathogen, Fecal Indicators, And Real-Time Quantitative PCR Genetic Markers In Manure Amended Soils. APPLIED AND ENVIRONMENTAL MICROBIOLOGY. American Society for Microbiology, Washington, DC, 77(14):4839-4848, (2011).
Impact/Purpose:
To compare the persistence and decay rate coefficients of bacterial pathogens, FIB, and emerging qPCR genetic markers in agricultural soils of various temperatures and moisture contents amended with swine or cattle manure at agronomic rates.
Description:
This study examined persistence and decay of bacterial pathogens, fecal indicator bacteria, and emerging real-time quantitative PCR (qPCR) genetic markers for rapid detection of fecal pollution in manre-amended agricultural soils. Known concentrations of transformed green fluorescent protein-expressing Escherichia coli O157:H7 and red fluorescent protein-expressing Salmonella enterica serovar Typhimurium were added to laboratory-scale manure-amended soil microcosms with moisture contents of 60% or 80% field capacity, and incubated at temperatures of -20oC, 10oC, or 25oC for 120 days. A two-stage first-order decay model was used to determine decay rate coefficients for each organism and qPCR genetic marker in each treatment. Increasing temperature and decreasing moisture content increased first stage decay rate coefficients and reduced transition times, but did not affect the second stage decay rate coefficient. Soil and manure properties exerted important effects on both the first and second stage decay rate coefficients and transition times. Genetic markers for Enterococcus spp., E. coli, and Bacteroidales exhibited similar decay rate coefficients as E. coli O157:H7, but not S. enterica serovar Typhimurium, and persisted at detectable levels longer than both pathogens. Concentrations of the pathogens and qPCR genetic markers were correlated (r=0.528-0.745). Host-associated qPCR genetic martkers decayed to non-detectable concentration long before other fecal indicators, Salmonella enterica serovar Typhimurium, and E. coli O157:H7. Although good indicators of point source or recent nonpoint source fecal contamination events, these host-associated qPCR genetic markers may not be reliable indicators of nonpoint source fecal contamination events that occur weeks following land application of manure.
