Title: Persistence of Escherichia coli and Attenuated E. coli O157:H7 in manure-enriched soils in the Eastern Shore of Maryland Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 22, 2013
Publication Date: N/A
Technical Abstract: Many fields in the Delmarva Peninsula are fertilized with poultry litter and other animal manures. Contamination of fresh produce by pathogens present in untreated animal manures is a major food safety risk concern. This study investigated the 1) survival of non-pathogenic E. coli (Ec) and attenuated E. coli O157:H7 (attO157) in soils amended with poultry litter (PL), dairy manure (DM), dairy manure liquid (DL), or horse manure (HM) and 2) compared the survival of Ec and attO157:H7 in manure-amended soil. Field plots (Othello soil) were amended with PL, DM, DL, or HM. Inocula containing equal numbers of three rifampicin-resistant (RifR) strains of Ec and two attO157-RifR strains grown in poultry-litter extract, were spray-inoculated (1-L per 2 m2) with low, 2.1x106 CFU/mL, or high, 6.4x108 CFU/mL, cell densities. Soil samples collected periodically 0-154 days post-inoculation (dpi) were analyzed for viable Ec and att0157 by direct plating and/or mini-MPN. Persistence of all strains was influenced by manure type, inocula concentration, and environmental factors. Populations declined more rapidly in DM compared to other treatments, except non-manured soils. By 7-dpi, all strains from both inoculum-level treatments declined to =1CFU (MPN) gdry soil-1 (gds-1), except DL and PL, which, unlike other manure treatments, increased after rainfall. Populations at 28-dpi and thereafter, continued at ca. =1CFU (MPN) gds-1. No Ec or attO157 were found in uninoculated control soil. Manure type and environmental factors influenced survival of E. coli in soil, with attO157 declining more rapidly than Ec. Both Ec and attO157 survived at higher populations in manure-amended soils compared to non-amended soils, indicating the effect manure has in extending the survival of bacteria in soils. These findings should be taken into consideration when setting guidelines for fresh produce safety relative to manure application to soil as stated in proposed FDA standards.