Abstract
The aim of this study was to analyze the occurrence of sulfonamide resistance genes (sul1–3) and other genetic elements as antiseptic resistance gene (qacEΔ1) and class 1 and class 2 integrons (int1–2) in the upper layer of substrate and in the effluent of microcosm constructed wetlands (CWs) treating artificial wastewater containing diclofenac and sulfamethoxazole (SMX), which is a sulfonamide antibiotic. The bacteria in the substrate and in the effluents were equipped with the sul1–2, int1, and qacEΔ1 resistance determinants, which were introduced into the CW system during inoculation with activated sludge and with the soil attached to the rhizosphere of potted seedlings of Phalaris arundinacea ‘Picta’ roots (int1). By comparing the occurrence of the resistance determinants in the upper substrate layer and the effluent, it can be stated that they neither were lost nor emerged along the flow path. The implications of the presence of antibiotic resistance genes in the effluent may entail a risk of antibiotic resistance being spread in the receiving environment. Additionally, transformation products of SMX were determined. According to the obtained results, four (potential) SMX transformation products were identified. Two major metabolites of SMX, 2,3,5-trihydroxy-SMX and 3,5-dihydroxy-SMX, indicated that SMX may be partly oxidized during the treatment. The remaining two SMX transformation products (hydroxy-glutathionyl-SMX and glutathionyl-SMX) are conjugates with glutathione, which suggests the ability of CW bacterial community to degrade SMX and resist antimicrobial stress.
Highlights
Antimicrobial agents, together with antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), have been widely detected in the clinical settings and in different environmental compartments (Aukidy et al 2012; Ratola et al 2012; Padhye et al 2013; Hsu et al 2014)
The removal of DCF is not going to be mentioned in this article, because its effect on the antimicrobial resistance in bacteria was beyond the scope of this study
The presence of pharmaceutical compounds (PhCs) in the feed did not affect the removal of chemical oxygen demand (COD), N-NH4, total nitrogen (TN), and P-PO4 (Nowrotek et al 2016) but affected significantly the removal of total organic carbon (TOC) and NNO3
Summary
Antimicrobial agents, together with antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), have been widely detected in the clinical settings and in different environmental compartments (Aukidy et al 2012; Ratola et al 2012; Padhye et al 2013; Hsu et al 2014). Due to serious infections caused by multidrug-resistant bacteria, in 2014, the World Health Organization identified antimicrobial resistance as one of the most critical challenges and serious threats to the global public health (World Health Organization 2014) Currently, both ARB and ARGs are regarded as emerging environmental contaminants, with possible implications for human health and ecological status of the environment (Sharma et al 2016). Wastewater treatment plants significantly reduce the load of bacteria, the final effluents may contain ARB, sometimes even at higher concentrations than in the raw wastewater (Zhang et al 2009; Novo and Manaia 2010; Luczkiewicz et al 2010; Galvin et al 2010; Mokracka et al 2012; Pruden et al 2012) To understand this phenomenon, particular attention has been given to the presence of selective pressure and mobile genetic elements (MGEs), which contribute to dissemination of resistance genes. Most previously described class 2 integrons contain the same array of four gene cassettes, three antibiotic resistance gene cassettes (dfrA1, sat, and aadA1), conferring resistance to trimethoprim, streptothricin, and spectinomycin/streptomycin, respectively, and the orfX cassette of unknown function (Flores et al 1990)
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