Fate of antibiotic resistant bacteria in two different constructed wetland types

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

Würzburg

Conferencia; 5 th Joint Conference of the DGHM & VAAM VAAM Annual Meeting 2017 69 th Annual Meeting of the DGHM; 2017

German Society for Hygiene and Microbiology (DGHM); Association for General and Applied Microbiology (VAAM)

Introduction: Wastewater treatment plants are known hotspotsfor the development and spreading of antibiotic resistant bacteria(ARB). Bacterial exchange of antibiotic resistance genes (ARG)might play an important role in these systems due to co-occurrence of high abundances of microorganisms and varioustypes of environmental stress.Constructed wetlands (CWs) are considered an alternativewastewater treatment option for removal of ARB and ARG,taking advantage of the ecosystems´ services that resemble thoseof natural wetlands. Thus, tracking ARB/ARG in CWs is ofadditional relevance for understanding better their fate in theenvironment. Here, we focused on bacterial resistance tosulfamethoxazole and trimethoprim, two antibiotics that arefrequently taken in combination and are on the World HealthOrganization´s List of Essential Medicines.Objectives: (1) To evaluate the fate of ARB/ARG in two differenttypes of CWs; (2) To elucidate to what extent the presence ofantibiotics and other stress sources affect ARB diversity;(3) To unravel interactions of incoming bacteria with theresident/permanent microbial community of the wetlands, withmain focus on horizontal gene transfer.Materials and methods: Two pilot-scale CWs, planted withcommon reed and receiving the same pre-treated wastewater asinflow were investigated over a period of almost 3 years. One CWwas aerated (i.e. intensified), the other was not. Abundances ofsulfamethoxazole- and trimethoprim-resistant bacteria along theCWs´ flow paths were quantified by plating coupled withphylogenetic identification of resistant isolates. Respectiveresistance genes (sul-I, sul-II, dfrA1) were enumerated in CWsamples by qPCR analysis. The abundance of int1 was measuredas representative gene of a common mobile element carryingARGs, i.e. class I integron. Standard wastewater parameters incl.numbers of Escherichia coli (quantified by MPN counting andqPCR) were recorded and bacterial community profiling wascarried out via 454 pyrosequencing. Sulfamethoxazole andtrimethoprim concentrations were determined by LC-MS.Results: A significant attenuation of ARB/ARG occurred in bothwetlands, the magnitude of which was larger in the aerated one. Inthis CW, the abundances of ARB/ARG fluctuated along the flowpath. This fluctuation varied for sul genes and dfrA1 andrespective ARB, suggesting that stress factors may influenceARGs differently, according to the genetic context.Conclusions: CWs are a suitable technology to attenuate ARBnumbers from wastewater, with intensified systems performingbetter. Further analysis should be done to evaluate horizontal genetransfer within the wetlands and to which extent this is influencedby stress factors in order to optimize water treatment by the meansof this inexpensive technology.p { margin-bottom: 0.25cm; line-height: 120%; background: transparent }p { margin-bottom: 0.25cm; line-height: 120%; background: transparent }