Fate of sulfamethoxazole and trimethoprim resistance in two constructed wetland types

C. KNECHT; H. DAMBECK; M. KRUEGER; J. NICKOLAUS; A. AHMED; S. KELLMANN; I. MÄUSEZAHL; M. MOEDER; J. NIVALA ; O. ADELOWO; J. MÜLLER

Lansing

Simposio; 4th International Symposium on the Environmental Dimension of Antibiotic Resistance (EDAR4); 2017

Wastewater treatment plants are known hotspots for the development and spreading of antibiotic resistant bacteria (ARB). Genetic exchange might play an important role in these systems due to co-occurrence of high abundances of microorganisms and various types of environmental stress.Constructed wetlands (CWs) are considered an alternative wastewater treatment option for removal of ARB and antibiotic resistance genes (ARG), taking advantage of the ecosystems? services that resemble those of natural wetlands. Studying ARB/ARG in CWs is of additional relevance as it may enhance our understanding of their fate in the environment.Here, we aimed (1) to evaluate the fate of bacterial resistance to sulfamethoxazole (SMX) and trimethoprim (TMP) in two types of CWs, and (2) to elucidate to what extent the presence of SMX/TMP and other stress sources affect ARB diversity with a particular focus on horizontal gene transfer.Two pilot-scale CWs receiving the same wastewater as inflow were investigated over a period of 3 years. One CW was aerated (i.e. intensified), the other was not. Abundances of SMX- and TMP-resistant bacteria along the CWs? flow paths were quantified by plating coupled with phylogenetic identification of resistant isolates. Respective resistance gene markers (sul alleles, dfrA1, int1) were enumerated by qPCR. Standard wastewater parameters incl. numbers of Escherichia coli were recorded and bacterial community profiling was carried out via 454 pyrosequencing. SMX and TMP concentrations were determined by LC-MS.ARB/ARG were attenuated by up to 4 orders of magnitude, with the aerated systems performing better. Only in this CW, the abundances of sul, int1, and SMX R -bacteria (but not dfrA1 and TMP R ) increased in the first portion of the flow path. Our findings indicate that stress factors other than the presence of antimicrobials influence strongly the abundances of ARGs in wastewater treatment systems, and that the respective genetic and organismal context is of high importance.