Erickson Marilyn C, Smith Chris, Jiang Xiuping, Flitcroft Ian D, Doyle Michael P
Center for Food Safety and Department of Food Science and Technology, University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA.
Food Safety Net Services, Atlanta Laboratory, 60 Chamisa Road, Suite 201, Covington, Georgia 30016, USA.
J Food Prot. 2015 Feb;78(2):302-10. doi: 10.4315/0362-028X.JFP-14-288.
Heat is the primary mechanism by which aerobic composting inactivates zoonotic bacterial pathogens residing within animal manures, but at sublethal temperatures, the time necessary to hold the compost materials to ensure pathogen inactivation is uncertain. To determine the influence of the type of nitrogen amendment on inactivation of Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7 in compost mixtures stored at sublethal temperatures, specific variables investigated in these studies included the animal source of the manure, the initial carbon/nitrogen (C:N) ratio of the compost mixture, and the age of the manure. Salmonella and L. monocytogenes were both inactivated more rapidly in chicken and swine compost mixtures stored at 20°C when formulated to an initial C:N ratio of 20:1 compared with 40:1, whereas a C:N ratio did not have an effect on inactivation of these pathogens in cow compost mixtures. Pathogen inactivation was related to the elevated pH of the samples that likely arises from ammonia produced by the indigenous microflora in the compost mixtures. Indigenous microbial activity was reduced when compost mixtures were stored at 30°C and drier conditions (<10% moisture level) were prevalent. Furthermore, under these drier conditions, Salmonella persisted to a greater extent than L. monocytogenes, and the desiccation resistance of Salmonella appeared to convey cross-protection to ammonia. Salmonella persisted longer in compost mixtures prepared with aged chicken litter compared with fresh chicken litter, whereas E. coli O157:H7 survived to similar extents in compost mixtures prepared with either fresh or aged cow manure. The different responses observed when different sources of manure were used in compost mixtures reveal that guidelines with times required for pathogen inactivation in compost mixtures stored at sublethal temperatures should be dependent on the source of nitrogen, i.e., type of animal manure, present.
热量是有氧堆肥使动物粪便中存在的人畜共患细菌病原体失活的主要机制，但在亚致死温度下，保持堆肥材料以确保病原体失活所需的时间尚不确定。为了确定氮素添加类型对亚致死温度下储存的堆肥混合物中沙门氏菌、单核细胞增生李斯特菌和大肠杆菌O157:H7失活的影响，这些研究中调查的具体变量包括粪便的动物来源、堆肥混合物的初始碳氮比（C:N）以及粪便的存放时间。与初始C:N比为40:1相比，当配方为初始C:N比为20:1时，沙门氏菌和单核细胞增生李斯特菌在20°C储存的鸡和猪堆肥混合物中失活更快，而C:N比对这些病原体在牛粪堆肥混合物中的失活没有影响。病原体失活与样品pH值升高有关，这可能是由于堆肥混合物中本地微生物产生的氨所致。当堆肥混合物在30°C储存且普遍存在较干燥条件（<10%水分含量）时，本地微生物活性降低。此外，在这些较干燥条件下，沙门氏菌比单核细胞增生李斯特菌持续存在的时间更长，并且沙门氏菌的抗干燥性似乎对氨具有交叉保护作用。与新鲜鸡粪相比，沙门氏菌在用陈旧鸡粪制备的堆肥混合物中持续存在的时间更长，而大肠杆菌O157:H7在用新鲜或陈旧牛粪制备的堆肥混合物中存活程度相似。当堆肥混合物中使用不同来源的粪便时观察到的不同反应表明，亚致死温度下储存的堆肥混合物中病原体失活所需时间的指导方针应取决于氮源，即存在的动物粪便类型。
