Abstract
The environment harbours a significant diversity of uncultured bacteria and a potential source of novel and extant resistance genes which may recombine with clinically important bacteria disseminated into environmental reservoirs. There is evidence that pollution can select for resistance due to the aggregation of adaptive genes on mobile elements. The aim of this study was to establish the impact of waste water treatment plant (WWTP) effluent disposal to a river by using culture independent methods to study diversity of resistance genes downstream of the WWTP in comparison to upstream. Metagenomic libraries were constructed in Escherichia coli and screened for phenotypic resistance to amikacin, gentamicin, neomycin, ampicillin and ciprofloxacin. Resistance genes were identified by using transposon mutagenesis. A significant increase downstream of the WWTP was observed in the number of phenotypic resistant clones recovered in metagenomic libraries. Common β-lactamases such as blaTEM were recovered as well as a diverse range of acetyltransferases and unusual transporter genes, with evidence for newly emerging resistance mechanisms. The similarities of the predicted proteins to known sequences suggested origins of genes from a very diverse range of bacteria. The study suggests that waste water disposal increases the reservoir of resistance mechanisms in the environment either by addition of resistance genes or by input of agents selective for resistant phenotypes.
Highlights
The growing number of bacteria resistant to multiple antibiotics pose a great risk to both animal and human health, yet despite this the role of the environment in the dissemination of antibiotic resistance genes is still largely unknown (Wellington et al, 2013)
In this study we aimed to investigate the impact of waste water treatment plant (WWTP) effluent on the resistome of a river, with the hypothesis that antibiotic resistance gene abundance and diversity would be significantly impacted by the effluent outflow
Using the average genome size of E. coli (4.6 Mb) it can be estimated that the Downstream samples (DS) library consisted of approximately 1826 bacterial genomes and the Upstream samples (US) library consisted of approximately 2043 bacterial genomes
Summary
The growing number of bacteria resistant to multiple antibiotics pose a great risk to both animal and human health, yet despite this the role of the environment in the dissemination of antibiotic resistance genes is still largely unknown (Wellington et al, 2013). Anthropogenic activities such as agriculture increase the load of environmental antibiotic resistant bacteria with recent reports of diverse resistance genes present in farm environments (Zhu et al, 2013) and increased levels of antibiotic resistance genes in soil following the application of manure (Byrne-Bailey et al, 2011).
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