Thermal inactivation of desiccation-adapted Salmonella spp. in aged chicken litter was investigated in comparison with that in a nonadapted control to examine potential cross-tolerance of desiccation-adapted cells to heat treatment. A mixture of four Salmonella serovars was inoculated into the finished compost with 20, 30, 40, and 50% moisture contents for a 24-h desiccation adaptation. Afterwards, the compost with desiccation-adapted cells was inoculated into the aged chicken litter with the same moisture content for heat treatments at 70, 75, 80, 85, and 150°C. Recovery media were used to allow heat-injured cells to resuscitate. A 5-log reduction in the number of the desiccation-adapted cells in aged chicken litter with a 20% moisture content required >6, >6, ϳ4 to 5, and ϳ3 to 4 h of exposure at 70, 75, 80, and 85°C, respectively. As a comparison, a 5-log reduction in the number of nonadapted control cells in the same chicken litter was achieved within ϳ1.5 to 2, ϳ1 to 1.5, ϳ0.5 to 1, and <0.5 h at 70, 75, 80, and 85°C, respectively. The exposure time required to obtain a 5-log reduction in the number of desiccation-adapted cells gradually became shorter as temperature and moisture content were increased. At 150°C, desiccation-adapted Salmonella cells survived for 50 min in chicken litter with a 20% moisture content, whereas control cells were detectable by enrichment for only 10 min. Our results demonstrated that the thermal resistance of Salmonella in aged chicken litter was increased significantly when the cells were adapted to desiccation. This study also validated the effectiveness of thermal processing being used for producing chicken litter free of Salmonella contamination. Chicken litter is a waste by-product of poultry production and is comprised of feces, wasted feeds, bedding materials, and feathers (1). More than 14 million tons of chicken litter is produced annually in the United States (2). Chicken litter is usually recycled as an organic fertilizer or soil amendment for direct application to agricultural land (3). However, chicken litter may contain loads of human pathogens, such as Salmonella spp., that have great potential to directly or indirectly contaminate fresh produce and cause food-borne disease outbreaks (1). Currently, high-temperature processing is the most commonly applied method to reduce or eliminate potential pathogens in chicken litter (1, 4).Some microorganisms become acclimatized to desiccation stress in a dry environment, and induction of the desiccation stress response in bacterial cells makes them more resistant to the dry condition in which they are present (5). Most importantly, exposure to a single stress is found to be associated with the development of cross-tolerance to multiple unrelated stresses (6). Using laboratory models, various researchers have demonstrated that the desiccated cells exhibit increased thermal resistance (6-8). Previous thermal-inactivation studies on bacterial pathogens in chicken litter have used only nonstressed cells (1, 4). Therefore, to si...
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...
This study investigated the survival of Escherichia coli O157:H7 and Salmonella Typhimurium in finished dairy compost with different particle sizes during storage as affected by moisture content and temperature under greenhouse conditions. The mixture of E. coli O157:H7 and S. Typhimurium strains was inoculated into the finished composts with moisture contents of 20, 30, and 40%, separately. The finished compost samples were then sieved into 3 different particle sizes (>1000, 500-1000, and <500 μm) and stored under greenhouse conditions. For compost samples with moisture contents of 20 and 30%, the average Salmonella reductions in compost samples with particle sizes of >1000, 500-1000, and <500 μm were 2.15, 2.27, and 2.47 log colony-forming units (CFU) g(-1) within 5 days of storage in summer, respectively, as compared with 1.60, 2.03, and 2.26 log CFU g(-1) in late fall, respectively, and 2.61, 3.33, and 3.67 log CFU g(-1) in winter, respectively. The average E. coli O157:H7 reductions in compost samples with particle sizes of >1000, 500-1000, and <500 μm were 1.98, 2.30, and 2.54 log CFU g(-1) within 5 days of storage in summer, respectively, as compared with 1.70, 2.56, and 2.90 log CFU g(-1) in winter, respectively. Our results revealed that both Salmonella and E. coli O157:H7 in compost samples with larger particle size survived better than those with smaller particle sizes, and the initial rapid moisture loss in compost may contribute to the fast inactivation of pathogens in the finished compost. For the same season, the pathogens in the compost samples with the same particle size survived much better at the initial moisture content of 20% compared to 40%.
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