Abstract:

Antimicrobial resistance poses a huge threat to human health worldwide. Soil, especially the agricultural soil, represents an important sources and reservoir for antibiotic resistance. It is important to understand the transmission mechanisms of antibiotic resistance genes (ARGs) in the soil for reducing the risk of dissemination of ARGs. The accumulation, transfer and elimination characteristics of ARGs in the soil are reviewed by summarizing and analyzing the relevant literature. By analyzing the available studies, it is found that the soil in agricultural and economically developed areas has become a hot area for the accumulation of ARGs. The application of organic fertilizer and sewage irrigation caused the continuous accumulation of ARGs in soil, and its abundance reached 102 gene copies/16S rRNA gene copies. Intracellular antibiotic resistance genes (iARGs) and extracellular free antibiotic resistance genes (eARGs) are the two different forms of ARGs, among which iARGs is the main one. iARGs spread in soil through conjugation transfer and transduction, with conjugation transfer being the most studied and dominant horizontal transfer mode. In addition, eARGs spread in soil through transformation. Soil extracellular DNA can remain in the soil for months or even more than a year, however, natural transformation of eARGs is not often detected due to the limitations in detection methods, so the risk of eARGs transmission in the soil has been neglected. The fate of exogenous ARGs entering soil is affected by ARGs species, forms, soil characteristics, pollutants, etc. The period from the gradual death of exogenous bacteria to the gradual degradation of free DNA are important time point nodes for whether exogenous ARGs can transfer in soil, and it is likely to be the key time to control the spread of ARGs in soil. At present, research on the elimination mechanism of host bacteria carrying ARGs into the soil is still in the initial stage, and in-depth studies are needed. Furthermore, the intensification measures for soil ARGs elimination mainly include agronomic changes, biochar application, phage therapy, etc., but with variable and limited effects. Consequently, future research should pay attention to the environmental effects of free eARGs, strengthen studies on the key factors influencing the propagation of ARGs in the soil and develop new enhancement measures to eliminate ARGs.

Key words: soil, intracellular antibiotic resistance genes, extracellular antibiotic resistance gene, horizontal gene transfer, elimination mechanism

摘要：

细菌耐药性给人类健康及公共卫生带来巨大的威胁。土壤尤其是农业土壤是环境中抗生素抗性重要的源库。为减少抗生素抗性基因（ARGs）的传播风险，了解其在土壤中的传播规律非常重要。通过总结分析国内外发表的相关文献，对目前ARGs在土壤中的积累、转移情况及消减特征进行了综述。已有调查结果发现，农业发达及经济发地区土壤是ARGs积累的热区。有机肥施用及污水灌溉等原因导致ARGs在土壤中持续积累，其丰度可达10² gene copies/16S rRNA gene copies。胞内抗生素抗性基因（iARGs）、胞外游离抗生素抗性基因（eARGs）是ARGs的两种赋存形态，其中，iARGs是主要的赋存形态。iARGs通过接合转移、转导在土壤中传播，其中接合转移是目前研究最多及最主要的水平转移方式。eARGs通过转化在土壤中传播。胞外DNA可以在土壤中留存几个月甚至一年以上，由于检测方法的限制eARGs在土壤中的自然转化并不经常被发现，因此，对土壤eARGs的风险研究有所忽略。外源ARGs进入土壤后的命运受到ARGs种类、形态、土壤特性、污染物等因素的影响。ARB进入土壤后逐渐死亡及游离DNA逐渐降解的这一时间段是外源ARGs能否在土壤中传播的重要时间节点，很有可能成为控制ARGs在土壤中传播的关键节点。目前关于携带ARGs的宿主细菌进入土壤后的消减规律的研究还处于起步阶段，仍需开展深入的研究。针对土壤ARGs消减的强化措施主要包括改变农艺措施、施加生物炭、噬菌体疗法等，但效果不一且有限。在未来的研究中应对游离的eARGs产生的环境效应给予重视，加强对ARGs在土壤中传播的关键影响因子的研究并开发新的强化措施以加快ARGs的消减。

关键词: 土壤, 胞内抗生素抗性基因, 胞外抗生素抗性基因, 水平基因转移, 消减机制