Fate of Escherichia coli O157:H7 during On-Farm Dairy Manure–Based Composting

Abstract

Studies were conducted to determine the fate of Escherichia coli O157:H7 in dairy manure–based compost in a field setting. Two trials were performed involving duplicate compost heaps constructed at an outdoor fenced site. The compost heaps were composed of dairy manure, old hay, feed waste, a mixture of sawdust and calf feces, and fresh hay. Samples of the composting mixture were inoculated with stx-negative E. coli O157:H7 B6914 at initial concentrations of 107 and 105 CFU/g for trial 1 and trial 2, respectively. Individual sample bags were placed on the surface and at three locations (top, center, and bottom) within each heap. Although the compost heaps achieved temperatures of 50°C or above at all internal locations for at least 7 days, temperature stratification was observed. In trial 1, E. coli O157:H7 was detected by enrichment through 14 days within the heaps. When inoculated with 105 CFU/g in trial 2, E. coli O157:H7 was detected only through days 2, 2, and 5 at the top, center, and bottom locations, respectively. For both trials, the pathogen survived at the heap's surface for up to 4 months. The indicator commensal E. coli and coliforms were inactivated at a rate similar to that for E. coli O157:H7. Results indicate that composting, with periodic heap turning, can be a practical approach to inactivating E. coli O157:H7 in cattle wastes on the farm. Our data also suggest when compost heaps are not turned, E. coli O157:H7 may survive for months at the heap surface.