Effect of wastewater colloids on membrane removal of antibiotic resistance genes Maria V. Riquelme Breazeal, John T. Novak, Peter J. Vikesland, Amy Pruden* Via Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, VA 24061, USA article info Article history: Received 21 June 2012 Received in revised form 21 September 2012 Accepted 22 September 2012 Available online 4 October 2012 Keywords: Antibiotic resistance genes Wastewater colloids Microfiltration Ultrafiltration abstract Recent studies have demonstrated that wastewater treatment plants (WWTPs) signifi- cantly alter the magnitude and distribution of antibiotic resistance genes (ARGs) in receiving environments, indicating that wastewater treatment represents an important node for limiting ARG dissemination. This study examined the potential for membrane treatment of microconstituent ARGs and the effect of native wastewater colloids on the extent of their removal. Plasmids containing vanA (vancomycin) and bla TEM (b-lactam) ARGs were spiked into three representative WWTP effluents versus a control buffer and tracked by quantitative polymerase chain reaction through a cascade of microfiltration and ultrafiltration steps ranging from 0.45 mm to 1 kDa. Significant removal of ARGs was ach- ieved by membranes of 100 kDa and smaller, and presence of wastewater colloids resulted in enhanced removal by 10 kDa and 1 kDa membranes. ARG removal was observed to correlate significantly with the corresponding protein, polysaccharide, and total organic carbon colloidal fractions. Alumina membranes removed ARGs to a greater extent than polyvinylidene fluoride membranes of the same pore size (0.1 mm), but only in the presence of wastewater material. Control studies confirmed that membrane treatment was the primary mechanism of ARG removal, versus other potential sources of loss. This study suggests that advanced membrane treatment technology is promising for managing public health risks of ARGs in wastewater effluents and that removal may even be enhanced by colloids in real-world wastewaters. ª 2012 Elsevier Ltd. All rights reserved. 1. Introduction Antibiotic resistance and, particularly, multidrug resistance, is an increasingly critical problem affecting human health (Davies and Davies, 2010). Globally, antibiotic resistance has been re- ported to be widespread (Allen et al., 2010) and on the rise (Zhang et al., 2006). Although most attention has been focused on nosocomial (i.e., hospital acquired) infections, environmental factors are also important contributors to the transport and spread of antibiotic resistance in the community (Larson, 2007). Recent studies have demonstrated that wastewater treatment plants can significantly alter the magnitude and distribution of antibiotic resistance genes (ARGs) in receiving environments (Storteboom et al., 2010). Given that antibiotic resistant bacteria (ARB) and ARGs of clinical concern have been documented to arise from environmental sources (Martinez, 2008), there is growing interest in limiting dissemination pathways between humans and the environment (Baquero et al., 2008). Thus, wastewater treatment plants may represent an important node for limiting the spread of antibiotic resistance. The presence of low levels of ARB and ARGs in wastewater is inevitable and several studies have documented their * Corresponding author. Tel.: þ1 540 231 3980. E-mail addresses: mvpr@vt.edu (M.V. Riquelme Breazeal), jtnov@vt.edu (J.T. Novak), pvikes@vt.edu (P.J. Vikesland), apruden@engr. colostate.edu, apruden@vt.edu (A. Pruden). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 47 (2013) 130 e140 0043-1354/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2012.09.044