Evaluation of the Fate of Naturally Occurring Escherichia coli O157:H7 During Bovine Manure Composting Processes.

Foodborne illnesses associated with produce consumption have brought attention to livestock manure composts as potential sources of pathogens for the contamination of these crops.  Our objective was to determine the fate of naturally-occurring E. coli O157:H7 during “minimally managed” on-farm bovine manure composting.  Feedlot pen surface manure was screened to identify E. coli O157:H7-positive manure.  Using this manure, four piles of each of three different composting format treatments were constructed, in each of two replicate experiments.  Composting format treatments included: (1) turned piles of manure-hay mixtures, (2) static piles of manure-hay mixtures, and (3) static stockpiles of manure.  Temperatures in the top and toe of the piles during the 84-day composting period were recorded continuously by electronic dataloggers, and in pile centers by periodic measurement with an analog compost thermometer.  Four compost samples for microbial analyses were collected from each pile (two each from the top and toe) at 0, 3, 7, 14, 21, 28, 42, 56, and 84 days of composting.  Compost piles that were turned every two weeks achieved higher temperatures for longer periods in the tops and centers, than piles that were left static.  E. coli O157:H7 was not recovered from pile top samples of turned piles of manure-hay mixtures at day 28 and beyond, while pile top samples of static piles were positive for the pathogen up to day 42 (static manure stockpiles) and day 56 (static piles of manure-hay mixtures).  E. coli O157:H7 was recovered sporadically from pile toe samples of all treatments up to day 84.  Our results indicate that minimally managed composting of bovine manure can reduce E. coli O157:H7, but also demonstrate the importance of periodic turning of the piles to ensure that all parts of the mass are subjected to high temperatures, for more effective and rapid elimination of this pathogen.