This study investigated the presence of culturable bacterial pathogens, and antibiotic resistance and associated genes (quantitative PCR) in commercially available composted products from animal excrements or manure (n=7), urban wastes (n=1) or (sewage sludge) (n=1). Metals quantification and 16S rRNA-based bacterial community composition analyses supported the results to infer potential risks to downstream environments (e.g., soils). Bacilli and Actinomycetes were the dominant bacterial classes in seven composts, while two were dominated by different classes of Pseudomonadota or the class Bacteroidia. Salmonella spp. was not detected in all composts, meeting recommended quality criteria, while Escherichia coli and Listeria monocytogenes were only detected in the sewage sludge compost. The antibiotic resistance genes ermB and ermF were detected in most of the composts, and the antibiotic resistance gene sul1 and the intI1 gene (proxy for antibiotic resistance recombination) in all composts in the range of 6-9 log gene copy number/g dry weight. Listeria spp. and the gene bla_CTX-M were detected only in chicken/poultry composts suggesting increased risk. All composts, except the urban waste compost, presented at least one metal (zinc, copper, and/or cadmium) above the recommended value. The genes uidA, crAssphage, ermB and bla_CTX-M were negatively correlated with the abundance of total heterotrophs and moisture content, and the genes intI1 and sul1 were negatively correlated with the concentration of the metals Cr, Ni and Pb. Overall, the urban waste compost presented the best quality, exhibiting the lowest antibiotic resistance load. These findings alert for the fact that composts may contribute to the dissemination of antibiotic resistance, highlighting the need of regular assessment. It is suggested that multiple factors, including the raw materials, may influence the safety of the final compost, and the knowledge of the variables affecting compost safety need to be thoroughly investigated and understood.

中文翻译：

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动物、城市或污水污泥废物堆肥产品的细菌学安全和质量


本研究调查了来自动物排泄物或粪便 （n=7）、城市废物 （n=1） 或（污水污泥）（n=1） 的市售堆肥产品中可培养细菌病原体的存在，以及抗生素耐药性和相关基因 （定量 PCR）。金属定量和基于 16S rRNA 的细菌群落组成分析支持结果推断对下游环境（例如土壤）的潜在风险。芽孢杆菌和放线菌是 7 种堆肥中的主要细菌类别，而 2 种以不同类别的假单胞菌或拟杆菌类为主。并非所有堆肥中都检测到沙门氏菌属，符合推荐的质量标准，而大肠杆菌和单核细胞增生李斯特菌仅在污水污泥堆肥中检测到。在大多数堆肥中检测到抗生素耐药基因 ermB 和 ermF，在所有堆肥中检测到抗生素耐药基因 sul1 和 intI1 基因（抗生素耐药性重组的代理），范围为 6-9 对数基因拷贝数/g 干重。李斯特菌属和基因 bla_CTX-M 仅在鸡/家禽堆肥中检测到，表明风险增加。除城市垃圾堆肥外，所有堆肥的金属含量都至少高于推荐值（锌、铜和/或镉）。基因 uidA 、 crAssphage 、 ermB 和 bla_CTX-M 与总异养生物丰度和水分含量呈负相关，基因 intI1 和 sul1 与金属 Cr 、 Ni 和 Pb 浓度呈负相关。 总体而言，城市垃圾堆肥的质量最好，表现出最低的抗生素耐药量。这些发现提醒人们，堆肥可能有助于抗生素耐药性的传播，突出了定期评估的必要性。研究表明，包括原材料在内的多种因素可能会影响最终堆肥的安全性，需要彻底调查和了解影响堆肥安全的变量。