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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SPECTRE (SPEciation and dynamiCs of TRace Elements)

Teaser

Summary

European waste production (2.5 billion t in 2010) have been steadily increasing. There is now a global consensus on the need to recycle resources to ensure sustainable development and to close the loop in a circular economy. Agricultural recycling makes it possible to effectively and synergistically use livestock, urban and agro-industrial organic waste (OW), but the advantages of using OW as fertilizer and soil amendment (improvement of yields and/or soil quality) need to be assessed together with the potential environmental and toxicological impacts due to the presence of toxic elements. Among these pollutants, antibiotic resistance bacteria (ARB) and trace elements (TEs) are seen as two major threats to environmental and human health.

Antibiotic resistance is a major healthcare issue worldwide. Antimicrobial resistance is now recognised as one of the most serious global threats to human health. If left unchecked, 10 million deaths every year could be attributable to antimicrobial resistance by 2050. In the last 20 years, increasing numbers of human pathogens causing cutaneous infections, diarrhoea, etc. have become resistant to all existing antibiotics and a resistant gene can be disseminated worldwide in only two years.

The co-existence of trace elements (TEs) and bacteria in organic waste (OW) fosters the development of antibiotic resistant bacteria (ARB). There is growing concern that TEs, particularly copper (Cu) and zinc (Zn), function as selective agents in the maintenance and dissemination of antibiotic resistance in OWs. Surprisingly, to date, there have been no studies on the correlation between ARGs and different forms of TEs, i.e. their speciation in organic wastes.

Agricultural organic wastes recycling propagates antibiotic resistance and TEs. Agricultural recycling of OW as fertilizer on farmlands is a widespread practice which enables the recycling of resources to ensure sustainable development, and to deal with the steadily increasing production of waste worldwide. But OW application in crop fields can increase (i) ARB, ARG levels in the soil and (ii) soil Cu and Zn concentrations. Furthermore, recent studies revealed that ARGs were more abundant on vegetables harvested from soil fertilised with OWs as compared to vegetables grown on the control soil. The consumptions of such contaminated vegetables by humans or animals represents a potential route of exposure to ARGs.

Because antibiotic resistance is a major healthcare issue, it is crucial to identify which determinants lead to the selection of resistant bacteria. The lack of knowledge on the role of Cu and Zn speciation in the co-selection and dissemination of antibiotic resistance is an emerging scientific issue which needs to be addressed without delay.
In this project, I will attempt to answer the following scientific questions:
1. Is the development of resistance to antibiotics driven by the speciation of Cu/Zn in OWs?
2. Are the abundance and diversity of ARGs and the fate of Cu/Zn correlated over time in the OW-soil-plant system?

Work performed

The first objectives was to identify the links between trace element speciation and the development of bacterial resistance. First, organic wastes of societal and scientific relevance were selected and the abundance of the antibiotic resistant genes was characterized. In parallel, thin sections of organic wastes have been be used to assess the laterally-resolved trace elements speciation to explore the spatial heterogeneity of Cu and Zn species in organic wastes at the Âµm scale. The data treatment of this last experiment is still ongoing.
In addition to this initial experiments, two additional experiments were conducted with simplified systems: one with an municipal wastewater spiked with trace elements at concentrations.and one to determine if copper can enhance antibiotic resistance in resistant bacteria and/or induce antibiotic resistance in sensitive bacteria two strains of bacteria.
The first results confirm that metal pollutants induce significant increases in microbial resistance potential.

Final results

Next step of the project will be to devoted to the study of the Fate of trace elements and antibiotic resistant genes when organic wastes are applied to soils. The first aim will be to determine which parameters control the abundance of antibiotic resistant genes during organic wastes mineralisation. The hypothesis is that changes in the physical-chemical properties and/or in trace element availability during mineralisation boost the development of antibiotic resistant genes. The second aim will be to identify the links between trace element speciation and the development of bacterial resistance on the root surface of plants. The hypothesis is that resistance develops in the proximity of the trace elements and that trace elements speciation determines the selection pressure.