title: Determining thermal inactivation of Escherichia coli O157:H7 in fresh compost by simulating early phases of the composting process.
abstract: A three-strain mixture of Escherichia coli O157:H7 was inoculated into fresh dairy compost (ca. 10(7) CFU/g) with 40 or 50% moisture and was placed in an environmental chamber (ca. 70% humidity) that was programmed to ramp from room temperature to selected composting temperatures in 2 and 5 days to simulate the early composting phase. The surviving E. coli O157:H7 population was analyzed by direct plating and enrichment. Optimal and suboptimal compost mixes, with carbon/nitrogen (C/N) ratios of 25:1 and 16:1, respectively, were compared in this study. In the optimal compost mix, E. coli O157:H7 survived for 72, 48, and 24 h in compost with 40% moisture and for 72, 24, and 24 h with 50% moisture at 50, 55, and 60°C, respectively, following 2 days of come-up time (rate of heating up). However, in the suboptimal compost mix, the pathogen survived for 288, 72, and 48 h in compost with 40% moisture and for 240, 72, 24 h in compost with 50% moisture at the same temperatures, respectively. Pathogen survival was longer, with 5 days of come-up time compared with 2 days of come-up. Overall, E. coli O157:H7 was inactivated faster in the compost with 50% moisture than in the compost with 40% at 55 and 60°C. Both moisture and come-up time were significant factors affecting Weibull model parameters. Our results suggest that slow come-up time at the beginning of composting can extend pathogen survival during composting. Additionally, both the C/N ratio and the initial moisture level in the compost mix affect the rate of pathogen inactivation as well.
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina 29634, USA.
authors.forename: Randhir
authors.initials: R
authors.lastname: Singh
authors.forename: Jinkyung
authors.initials: J
authors.lastname: Kim
authors.forename: Marion W
authors.initials: MW
authors.lastname: Shepherd
authors.forename: Feng
authors.initials: F
authors.lastname: Luo
authors.forename: Xiuping
authors.initials: X
authors.lastname: Jiang
mesh_terms: D002244:Carbon / Q000378:metabolism; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000502:physiology* / Q000528:radiation effects*; D006358:Hot Temperature; D050296:Microbial Viability / Q000528:radiation effects*; D009584:Nitrogen / Q000378:metabolism; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology
chemical_list: D012987:Soil; D002244:Carbon; D009584:Nitrogen