Characterizing the antibiotic resistance genes in a river catchment: Influence of anthropogenic activities
Graphical abstract
Introduction
Antibiotics have been widely used in medical care, husbandry, aquaculture, and agriculture (Aarestrup et al., 2001). The 25%–75% of the used antibiotics in human or livestock which are excreted in intact form in feces and urine, resulted in the continuous discharge of antibiotics into the environment (Bu et al., 2013, Daughton and Ternes, 1999). The released antibiotics may accelerate the development and dissemination of antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment (Alonso et al., 2001). Moreover, ARGs can transfer between different bacterial strains through horizontal gene transfer (HGT) and migrate between connected aquatic systems. The wide spread of ARGs and ARB would increase the risk to human health because of the ineffectiveness of antibiotic for treating infectious bacterial diseases. Therefore, ARGs are considered to be the global emerging pollutants (Levy, 1998, Pruden et al., 2006).
With the increasing concern of ARGs, many studies have been conducted to investigate the occurrence of these emerging pollutants in various aquatic environments, including river delta (Jiang et al., 2013, Zheng et al., 2011), estuary (Zheng et al., 2011), groundwater (Chee-Sanford et al., 2001), and water supply reservoir (Huerta et al., 2013, Su et al., 2014). It has also been suggested that anthropogenic activities had significant influence on the occurrence and dissemination of ARGs in aquatic environment (Chen et al., 2013a, Su et al., 2014). Studies had been conducted in many specific contamination sources to reveal their contributions of ARG pollution in aquatic environment, including wastewater treatment plants (WWTPs) (LaPara et al., 2011), hospitals (Rodriguez-Mozaz et al., 2015), aquaculture farms (Gao et al., 2012), and livestock farms (Koike et al., 2007, Zhang et al., 2013b). However, the influence of these anthropogenic sources on the distribution of ARGs in a regional catchment was rarely reported.
The Beijiang River, one of the main tributaries flowing through the Pearl River Delta Region, is the most densely urbanized region in Southern China. Population density, as well as the number and diversity of potential pollution sources of ARGs and ARB varied from source to estuary, which make the Beijiang River a proper object to study the influence of anthropogenic activities on the distribution of ARGs on a regional scale. The objectives of the present study are (1) to investigate the profiles of ARGs along the Beijiang River, (2) to uncover the influence of anthropogenic activities on the distribution of ARGs, and (3) to identify the environmental factors affecting the distribution of ARGs in aquatic environment.
In this study, a total of 23 ARGs in 5 classes (sulfonamides, β-lactams, erythromycins, chloramphenicol, and tetracycline resistance genes) which has been found prevalent in surface water were investigated (Pei et al., 2006, Stoll et al., 2012) and covered the common used antibiotics in medical care and husbandry industry (Aydin et al., 2015, Cheng et al., 2013). For example, genes of sulI, sulII, tetA, tetB, tetC, tetG, tetM, tetO, tetW, and tetX were frequently detected in surface water and drinking water samples (Jiang et al., 2013). Among them, 5 ARGs with high frequency of detections (FODs) were selected for further quantification analysis with regard to their distribution and impacts by the potential pollution sources in the Beijiang River catchment.
Section snippets
Sample collection
A total of 38 surface water samples were collected using the glass samplers along the Beijiang River from its two separate sources (Sites S1 and S8) to the Pearl River Estuary (Site S43) near the South China Sea. The sampling campaign lasted for 7 days in March, 2013 to investigate the ARG profile in surface water in the dry season of the Beijiang River. The sampling sites were grouped into three categories: upstream area (Sites S1–S12), midstream area (Sites S13–S26), and downstream area (Sites
Occurrence of ARGs in the Beijiang River
A total of 23 ARGs were investigated, including 2 sulfonamide resistance genes (sulI, sulII), 3 β-lactam resistance genes (ampC, blaSHV and blaPSE-1), 3 chloramphenicol resistance genes (floR, catI and catII), 2 erythromycin resistance genes (ermA and ermB), and 13 tetracycline resistance genes (tetA, tetB, tetC, tetD, tetE, tetG, tetL, tetM, tetO, tetQ, tetS, tetW and tetX). Among them, 11 ARGs were commonly found in the samples with the frequency of detection (FOD) higher than 65% (Appendix A
Spatial distribution pattern of ARGs in the Beijiang River
To characterize the sampling sites in different pollution sources, cluster analysis was conducted based on the abundances of sul and tet genes in the sampling sites (Fig. 2). The sites can be divided into 4 clusters. Each cluster had distinct characteristics from others.
Sites in Cluster A were featured by the significantly high abundances of tetW. These sites distributed in nonferrous metal mining area (Sites S3 and S10), downstream of electric waste disposal area (Site S23) and proximity to
Conclusions
This study revealed the profiles of 23 ARGs in the Beijiang River and investigated the influence of anthropogenic activities on the distribution of ARGs. The occurrence, abundances, and diversity of ARGs in the Beijiang River were primarily ascribed to the population density and contamination sources like WWTPs, aquaculture farms, livestock wastewater, etc. Co-selection between heavy metal resistance genes and ARGs, and even between different ARGs also attributed to the increase of ARGs. Our
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Nos. 21177162 and 51579253). We thank the team of Dr. Yongde Zou from the Commodity Inspection and Quarantine in Nanhai, Foshan, for their assistance in the determinations of antibiotics in this project.
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