Wastewater treatment plants as critical reservoirs for resistance genes

Genes coding for antimicrobial resistance (AMR) pose a serious threat to human health, nd large international and national initiatives are addressing the density and potential control of AMR in natural populations (in Norway, the One Health initiatives). Wastewater sewer systems and treatment plants (WWTP) are hot spots for occurrence and spreading for AMR. Several studies have over the last years looked at the occurrence of antimicrobial comounds and bakteria known to be resistant to even multi-spectered antibacterial treatment, but less is known regarding the potential for spreading of AMR genes into natural and non-pathogenic bacterial populations. WWTP concentrate bacteria into sludge, and through that increase contact ad transfer potential of mobile genetic elements encoding AMR. A mathematical model that describes how genes responsible for antimicrobial resistance in bacteria spread in ordinary wastewater treatment systems has been developed. We use the model to study the importance of the main mechanisms for such spreading for the overall transfer of antimicrobial genes to natural populations of bacteria in these systems. Our results show that from a theoretical point of view, cell to cell contact is the most important way that genes are transferred along with transfer mediated by bacterial viruses (so called bacteriophages). We must, however, warn the reader that our investigations is purely theoretical, and the lack of experimental studies on the actual transfer in wastewater systems means that our model cannot be used as of now for evaluation of environmental and public health risk. Once relevant data are available, we will be able to use the model for prediction of such risks. Experiments that will help us get the model right is ongoing.

Vi har utført grunnforskning med anvendelser innen avløpsrensing som vil ha betydning både for forståelsen av spredning av gener som koder for antimikrobiell resistens i avløpsrenseanlegg og ved bruk av slam fra slike i landbruket. Gjennom samarbeid med våre regionale selskap for avløpsrensing (og slamdisponering) har prosjektet bidratt til bevisstgjøring av brukerne av slam og rensning av avløpsvann. To masteroppgaver og to PhD prosjekter i tilknytning til prosjektet. Post doc i prosjektet har utviklet kunnskaper, nettverk og resultater om modellering av slike system. Etablering av kompetanser innen modellering og eksperimentelle teknikker inngår her. Problemstillingen i prosjektet er kompleks og sammen med andre prosjekter i JPIAMR har vi identifisert viktige kunnskapshull og identifisert områder der denne forskningen bør videreutvikles. Metodologiske tilnærminger er utviklet og evaluert, og anbefalinger til videre eksperimentelle studier er av stor verdi.

Multi-resistant bacteria are a severe problem to modern healthcare. Wastewater treatment plants (WWTP) are nodal points where significant amount of microbial material is collected. WWTP, regardless of technology involved, separate wastewater constituents into an effluent water fraction, and a biosolids residual. It is the overall objective that the biosolids are treated and converted into a nutritional sludge to be reused in agricultural production. Sanitation of biofertilizer is usually performed via treatment at 70°C for 1 hour. However, other strategies need to be developed to assure that the frequency of resistance genes in the sludge is drastically reduced. So far, very few reports are present on the abundance of resistance genes in WWTP and sludge treatment processes, and even less information is available concerning possible treatments to actively reduce the content. In this project we will evaluate the transfer and transformation of genetic elements in WWTP and develop a model for this to be used for prediction of genetic element fate and effect. We will combine genetic element tracer studies in laboratory scale bioreactors, and develop a conceptual model for spreading and transformation within such systems. Furthermore, we plan to develop a predictive model that may be used to evaluate various treatment strategies for reduction of spreading of genetic elements coding for antimicrobial resistance. University of Stavanger is responsible for execution of laboratory scale spreading studies in WWTP model systems, and combine data from our and consortia member groups for development of the predictive model. This require the combination of bioprocess experimental studies and theoretical model development, studies that themselves individually challenging, and even more so when combined. We hope our contribution will help society in reducing the threat from multi-resistant bacteria on human health care through spreading via WWTP and biosolids reuse.