Short CommunicationAbundance of antibiotic resistance genes and bacterial community composition in wild freshwater fish species
Introduction
Although antibiotic resistance is an ancient and naturally occurring phenomenon widespread in bacterial communities (D'Costa et al., 2011), the intensification of anthropogenic activities has increased the prevalence of antibiotic-resistant bacteria and their antibiotic resistance genes (ARGs). The increasing number of publications and funded projects about antibiotic resistance reflect the current interest of the scientific community and society for tackling this growing global issue (Rizzo et al., 2013). Several studies have therefore been conducted to assess the emergence and prevalence of ARGs in both clinical and environmental bacterial strains (Cantón, 2009, Youenou et al., 2015). Considering that most antibiotics administered to human and animals are only partially metabolized and released to wastewater treatment plants where they are not completely removed (Gros et al., 2012), antibiotic residues may exert adverse effects on wild animals once they reach the receiving environment, such as rivers and reservoirs (Zhao et al., 2015). As a consequence, aquatic animals can potentially serve as reservoirs of resistant bacteria and ARGs.
Some studies have reported the presence of ARGs in farmed fish (Gao et al., 2012, Jiang et al., 2012, Deng et al., 2014, Muziasari et al., 2017), as well as in water and sediment samples from fish farms (Xiong et al., 2015). This is not surprise because fish under intensive production conditions are exposed to antibiotics, which are used as prophylactic agents and growth promoters, especially in countries with few regulations about the use of antibiotics (Pruden et al., 2013). However, to the best of our knowledge, no study has been focused on the abundance of ARGs in wild fish species. In fact, limited information is available on the role of wild animals in the ecology and evolution of antibiotic resistance (Arnold et al., 2016).
Given this, the present study aimed to determine the abundance of four ARGs and to examine bacterial community diversity associated with the intestinal mucus of wild freshwater fish species inhabiting two reservoirs. Genes conferring resistance to β-lactams (blaTEM), fluoroquinolones (qnrS), macrolides (ermB), and sulfonamides (sulI) were selected based on their clinical and environmental relevance. Moreover, these ARGs are usually located on conjugative plasmids, which may facilitate their transfer and spread within bacterial communities (Blair et al., 2015). It should be noted that freshwater fish species were collected from reservoirs with different level of pollution to understand whether and to what extent anthropogenic activities contribute to antibiotic resistance in wild aquatic organisms. Moreover, water and sediment samples were also collected to determine the level of antibiotic pollution in the surrounding environment.
Section snippets
Sampling and sample processing
Fish were collected from the Foix and La Llosa del Cavall reservoirs, both located in Catalonia (NE Spain), which represent ecosystems with high and low anthropogenic disturbance, respectively (Huerta et al., 2013). Specifically, common carp (Cyprinus carpio) were collected from the Foix reservoir whereas Ebro barbel (Luciobarbus graellsii) and brown trout (Salmo trutta) were collected from La Llosa del Cavall reservoir. In all cases, six specimens per each fish species were collected during
Quantification of ARGs
Four ARGs, including blaTEM, ermB, sulI and qnrS genes were quantified by qPCR in fish intestinal mucus samples. The 16S rRNA gene was also quantified to confirm the presence of bacterial DNA in all samples, which ranged from 1.1 × 107 to 4.1 × 108 gene copies per gram. Relative concentrations of ARGs, normalized to the 16S rRNA gene copies for comparative purposes, are shown in Fig. 1. The blaTEM gene was only detected in brown trout and Ebro barbel, which were collected from La Llosa del
Discussion
Although some studies have demonstrated the presence of ARGs in the intestinal microbiota of fish under intensive production conditions (Schmidt et al., 2000, Shah et al., 2012), no study has been focused on the abundance of ARGs in wild fish species. This study, therefore, investigated the abundance of four ARGs, as well as bacterial community composition in three freshwater fish species collected from two reservoirs. Water and sediments from these reservoirs were also collected and analyzed
Acknowledgments
This study was supported by the 1st Interdisciplinary Water Research Projects–ICRA Grants Program (RES2 project), the Generalitat de Catalunya (2014 SGR 291), the Spanish Ministry of Economy and Competitiveness through the SCARCE project (CSD2009-00065) and the Ramón y Cajal program (RYC-2011-08154 and RYC-2014-16707), and the European Union through the European Regional Development Fund (FEDER).
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