The occurrence and abundance of antibiotic resistance genes in rivers of tropical islands: a case of Hainan Island, China

In this study, the occurrence and distribution of 49 antibiotic resistance genes (ARGs) and two integrase genes ( intl1 , intl2 ) in three major rivers of Hainan Island, China, were investigated in July 2021, and to explore the spatial distribution of the target genes in the three rivers with the potential influencing factors such as regional characteristics and environmental factors. The results showed that a total of 46 ARGs and two integrase genes were detected in water and sediment, and the absolute abundance of ARGs ranged from 1.16 × 10 3 to 2.97 × 10 7 copies/L and 3.34 × 10 3 –1.55 × 10 7 copies/g. ARGs of macrolides, aminoglycosides, and sulfonamides were this study’s main types of ARGs. The aadA2 , tetE , ermF , tetX , aac(6′)-Ib , tetW , and qnrS genes are predominant ARGs in the water and sediment of the three rivers. The relative abundance of ARGs shows higher abundance in the midstream and downstream and lower abundance in the upstream and estuarine. After conducting a correlation analysis, it was found that there was a significant positive correlation between the ARGs detected in the water of the three main rivers. However, in sediment, tetC was negatively correlated with tetQ , macB was negatively correlated with ermF and ereA ( p < 0.05), while the remaining ARGs showed positive correlations. Specifically, there was no significant positive correlation between tetQ and tetC , macB and ereA , and ermF in the sediments. Among the nine environmental factors studied, pH was found to be the main factor associated with the occurrence of ARGs in the aquatic environment, but it was also significantly associated with only nine ARGs. Among the detected heavy metals, only Cd and Zn showed significant correlations with the two ARGs in the water bodies of the three main rivers. It indicated that the pollution of ARGs in the three major rivers was in the initial stage, the detection abundance was low, the influence of environmental factors was small, and the interaction between ARGs seemed to be the main driving force. This study provides a scientific basis for further understanding the occurrence of ARGs and their influencing factors in a tropical island environment, and lays a foundation for subsequent management.