Food Microbiology and Food Safety Unit, Division of Preventive Veterinary Medicine, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Japan.
Department of Bacteriology II, National Institute of Infectious Diseases, Tokyo, Japan.
PLoS One. 2024 May 21;19(5):e0301972. doi: 10.1371/journal.pone.0301972. eCollection 2024.
Livestock excrement is composted and applied to agricultural soils. If composts contain antimicrobial-resistant bacteria (ARB), they may spread to the soil and contaminate cultivated crops. Therefore, we investigated the degree of transmission of ARB and related antimicrobial resistance genes (ARGs) and, as well as clonal transmission of ARB from livestock to soil and crops through composting. This study was conducted at Rakuno Gakuen University farm in Hokkaido, Japan. Samples of cattle feces, solid and liquid composts, agricultural soil, and crops were collected. The abundance of Escherichia coli, coliforms, β-lactam-resistant E. coli, and β-lactam-resistant coliforms, as well as the copy numbers of ARG (specifically the bla gene related to β-lactam-resistant bacteria), were assessed using qPCR through colony counts on CHROMagar ECC with or without ampicillin, respectively, 160 days after compost application. After the application of the compost to the soil, there was an initial increase in E. coli and coliform numbers, followed by a subsequent decrease over time. This trend was also observed in the copy numbers of the bla gene. In the soil, 5.0 CFU g-1 E. coli was detected on day 0 (the day post-compost application), and then, E. coli was not quantified on 60 days post-application. Through phylogenetic analysis involving single nucleotide polymorphisms (SNPs) and using whole-genome sequencing, it was discovered that clonal blaCTX-M-positive E. coli and blaTEM-positive Escherichia fergusonii were present in cattle feces, liquid compost, and soil on day 0 as well as 7 days post-application. This showed that livestock-derived ARB were transmitted from compost to soil and persisted for at least 7 days in soil. These findings indicate a potential low-level transmission of livestock-associated bacteria to agricultural soil through composts was observed at low frequency, dissemination was detected. Therefore, decreasing ARB abundance during composting is important for public health.
家畜粪便经过堆肥处理后应用于农业土壤。如果堆肥中含有抗微生物药物的细菌（ARB），它们可能会传播到土壤中并污染种植的作物。因此，我们研究了ARB 及其相关抗微生物药物耐药基因（ARGs）通过堆肥从家畜向土壤和作物传播的程度，以及 ARB 从家畜到土壤和作物的克隆传播。这项研究是在日本北海道的酪农学园大学农场进行的。采集了牛粪便、固体和液体堆肥、农业土壤和作物样本。使用 qPCR 通过分别在含有或不含有氨苄青霉素的 CHROMagar ECC 上进行菌落计数，评估了大肠杆菌、大肠菌群、β-内酰胺类耐药大肠杆菌和β-内酰胺类耐药大肠菌群的丰度，以及 ARG（特别是与β-内酰胺类耐药菌相关的 bla 基因）的拷贝数，160 天后应用堆肥。在将堆肥应用于土壤后，大肠杆菌和大肠菌群数量最初增加，随后随着时间的推移而减少。bla 基因的拷贝数也观察到了同样的趋势。在土壤中，在 0 天（即堆肥应用后）检测到 5.0 CFU g-1 的大肠杆菌，然后在应用后 60 天未检测到大肠杆菌。通过涉及单核苷酸多态性（SNPs）的系统发育分析和全基因组测序，发现 blaCTX-M 阳性大肠杆菌和 blaTEM 阳性弗格森埃希氏菌的克隆 blaCTX-M 阳性大肠杆菌和 blaTEM 阳性弗格森埃希氏菌存在于牛粪便、液体堆肥和土壤中在第 0 天和第 7 天应用后。这表明，家畜来源的 ARB 通过堆肥从家畜传播到土壤，并在土壤中至少持续 7 天。这些发现表明，通过堆肥从家畜向农业土壤的低水平传播家畜相关细菌的现象时有发生，传播被检测到。因此，在堆肥过程中减少 ARB 的丰度对于公共卫生很重要。
