Fate of antibiotic resistant bacteria in two different constructed wetland types

CAMILA KNECHT; H. DAMBECK; M. KRÜGER; J. NICKOLAUS; A. AHMED; S. KELLMANN; I. MÄUSEZAHL; M. KÄSTNER; O. O. ADELOWO; J. NIVALA; J. A. MÜLLER

Jena

Conferencia; Annual Conference 2016 of the Association for General and Applied Microbiology (VAAM); 2016

Association for General and Applied Microbiology (VAAM)

Question: The current extensive release of antibiotic resistant bacteria (ARB),respectively antibiotic resistance genes (ARG), into the  environment is of significant concern. Here, we asked whether  constructed wetlands (CWs) are suitable to treat domestic wastewater containing ARB/ARG; i.e. which mechanisms are governing whether ARG are eliminated, maintained, multiplied, or distributed in near-natural habitats like CWs?Methods: Two pilot-scale horizontal subsurface flow CWs, planted withcommon reed (Phragmites australis) and receiving the same inflow(secondary clarifier effluent from a nearby wastewater treatment plant), were investigated over a sampling period of almost 2 years. One CW was aerated, the other was not. Abundances of sulfamethoxazole and trimethoprim resistant bacteria (SMX R and TMP R ) along the CWs? flow paths were quantified by plating coupled with phylogenetic identification of resistant isolates. Concomitantly, respective resistance genes (sul-I, sul-II, dfrA1) were enumerated by qPCR analysis. Those genes were selected as ARG indicators since they can be abundant in anthropogenic sources but are rare in native aquatic and terrestrial ecosystems as well have frequently different linkages to mobile genetic elements. In addition, standard wastewater parameters incl.numbers of Escherichia coli (quantified by MPN counting and qPCR) were recorded and bacterial community profiling was carried out via 454pyrosequencing.Results: The inflow displayed microbiological features typical of secondary treated wastewater, including abundances of the selected ARG ranging from ca. 1E+04 to 1E+05 copies/100 ml. In the non-aerated wetland there was a roughly-steady decline of the ARB/ARG by about 1 to 1.5 log units along the flow path. In contrast, in the aerated CW the numbers of SMX R , sul-I, and sul-II increased first till a maximum at about 2 m downstream from the influent before they decreased by about 2 log units. Furthermore, the SMX R speciesprofile changed thru the passage of the aerated wetland. No strong shift in sul hosts was observed for the non-aerated bed, or for dfrA1 in either CW. Total bacterial community profiles, enumerations of E. coli, and standard wastewater parameter indicate that the aerated CW became an unsuitable habitat for many bacteria present in the inflow at about the 2 m mark, while the non-aerated bed did not appear to constitute a particularly stressful habitat.Conclusion: The CW biotechnology appears to be a promising approach to attenuate or even eliminate ARG/ARB from wastewater. However, this study also provides evidence that common habitat stress may be a significant factor governing the dispersal of ARG when those are present in a mobile genetic context.