Our results revealed that a 7-log reduction of Salmonella can be achieved by exposing fresh chicken litter for 80.5 to 100.8, 78.4 to 93.1, and 44.1 to 63 min at 70, 75, and 80°C, respectively, depending on initial moisture contents. However, the aged chicken litter requires more heat treatment.A pproximately 14 million tons of poultry litter, most of which was broiler litter (68%), was produced on U.S. poultry farms in 1990, and over 90% of poultry litter is applied to agricultural land (22). However, the direct application of this waste material to agricultural land can be harmful to the environment due to nutrient and pathogenic microorganisms in runoff (14,29). Salmonella-contaminated litter can be a potential source of produce contamination in the agricultural field due to the prolonged survival of Salmonella in the environment (9, 17). Heat treatments are usually recommended to reduce or eliminate potential pathogenic microorganisms in animal wastes. To produce a heattreated product that tests negative or at less than the detection limit for Salmonella, the temperature range of 65 to 80°C for 30 to 60 min was recommended by different organizations or federal agencies (11,23,33). The California Leafy Green Marketing Agreement (LGMA) has a strict guideline for physically heattreated animal manure. A minimum temperature of 150°C for 60 min, resulting in a moisture content of less than 30%, and a negative result or a result that is less than the detection limit for fecal coliforms, Salmonella, and Escherichia coli O157:H7 are required (3). However, there were no defined heat sources (dry versus moist heat), varying time-temperature requirements, and microbial standards among the guidelines.Most research on heat inactivation of pathogens has shown that dry heat requires a much higher temperature than moist heat to achieve comparable pathogen inactivation in sludge (4,24,37). In contrast, there are few quantitative data on the effects of dry heat on pathogen inactivation. examined thermal inactivation of Salmonella artificially inoculated in sludge using dry heat. Salmonella populations were reduced by ca. 6 logs after 30 min and by more than 8 logs after 90 min at 80°C. Davey (8) calculated that the time required to inactivate clumps of bacteria heated in dry air is about 19 times more than in moist heat.The purpose of this study was to evaluate thermal inactivation of Salmonella spp. in chicken litter under different temperatures, moisture levels, and litter compositions.Preparation of chicken litter. Fresh chicken litter was collected daily from a chicken house of laying hens (single-comb white leghorns), which were raised on the Morgan poultry farm, Clemson, SC. The majority of the litter was feces mixed with a small amount of feathers and wasted feeds. The litter was dried under a hood until the moisture content was reduced to less than 30% and then ground to a particle size of less than 3 mm (sieve pore size, 3 by 3 mm). Aged chicken litter was collected from a local poultry farm (Westminster, SC) where 4...
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.
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 10(7) and 10(5) 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 degrees 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 10(5) 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.
Aims: The purpose of this study was to determine whether the methods used in compost operations of small and medium‐sized poultry forms resulted in the production of an amendment free of foodborne pathogens. Methods and Results: Nine compost heaps on five South Carolina poultry farms were surveyed at different stages of the composting process. Compost samples were analysed for coliforms and enriched for Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes. The waste materials and composting practices differed among the surveyed farms. On two farms, new materials were added to heaps that had previously completed the active composting phase. Five compost heaps did not reach an internal temperature of 55°C, and c. 62% of all internal samples in the first composting phase contained moisture contents <40%. Escherichia coli was detected in 63% of the surface samples (n = 38) and 9·8% of the internal samples (n = 82) from the first composting phase, as compared with 16·7% of the surface samples (n = 12) and 0% internal samples (n = 24) from the second composting phase. Salmonella was detected in 26 and 6·1% of all surface and internal samples collected from heaps in the first composting phase, respectively, but was absent in all compost samples undergoing a second composting phase. The predominant Salmonella serotypes were Thompson, Montevideo and Anatum. Neither E. coli O157:H7 nor L. monocytogenes was detected in any of the samples. Conclusions: Our results indicate that the conditions at the compost surface are suitable for pathogen survival, and the complete composting process can result in the elimination of pathogens in poultry wastes. Significance and Impact of the Study: This research provides information regarding the effectiveness of the composting practices and microbiological quality of poultry compost produced by small‐ and medium‐sized farms. Ensuring the safety of compost that may be applied to soils should be an integral part of preharvest food safety programme.
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