BIOCIDE

Background 

The emergence and global dissemination of antibiotic resistant bacteria has developed into a severe threat to public health, jeopardizing our ability to treat bacterial infections, cure cancer and perform advanced surgery, all of which are dependent on effective antibiotics.

Our extensive use of antibiotics and insufficient measures to prevent the spread of resistant bacteria are primary drivers of resistance. However, the external environment also contributes, partly  as a transmission route for several bacterial pathogens and also in the evolution and emergence of resistance in pathogens as the immense diversity of environmental bacteria serves as a source for resistance genes through horizontal gene transfer. A “one health perspective”, considering the ability of bacteria and genes to move between humans, animals and the external environment, is therefore needed to understand and efficiently manage resistance development.

Antibacterial Chemicals Drive Resistance 

Co-selection from antibacterial biocides, chemicals with antibacterial properties,  can drive resistance development. These include metals and numerous organic biocides used, for example, as disinfectants in health care, as antifoulants, as preservatives, or as antibacterial agents on clothes and in household products. In addition to their specific sites of applications, biocides are widely disseminated in the environment, particularly via wastewater streams, into waterways and eventually oceans. While well justified in certain settings (e.g. disinfection in hospitals), our extensive use is likely to promote resistance.

Mechanisms Behind Antibiotic Resistance

There are at least two main mechanisms by which biocides may co-select for antibiotic resistance. The first involves co-resistance, where the biocide resistance genes are present on the same, mobile genetic element (e.g., a plasmid) as the antibiotic resistance genes. Such co-localization will indirectly select for resistance. The second is referred to as cross-resistance where the biocide and the resistant bacteria share a common resistance mechanism (e.g., up-regulation of efflux pumps). For both these mechanisms, exposure to biocides will directly and inevitably enrich already co-resistant strains, and thus promote their dissemination and ultimately increase transmission risks.

In addition, there is evidence that the immense genetic diversity of the environmental microbiome contributes to emergence of novel mobile antibiotic resistance determinants in pathogens; these are less common evolutionary events but with potentially profound consequences. Here, selection from biocides could very well play a key role if cross-resistance is involved, while this is not the case for co-resistance – unless the different genes are linked from the very beginning. Therefore, understanding the relative roles of co- versus cross-resistance mechanisms in co-selection is essential to assess and manage different risk scenarios. Moreover, the mechanism of resistance and the involved genes remain unknown for most biocides, preventing us from evaluating the link to antibiotic resistance.

Horizontal Gene Transfers

Not only do biocides have the potential to select for resistance, but also to increase horizontal gene transfer, two processes that together can exacerbate the resistance problem. Typically, effects on horizintal gene transfers through conjugation have only been studied using model strains, limiting generalizations. Several biocides can generate intracellular reactive oxygen species  which, in turn, provoke an SOS response leading to plasmid transfer initiation. To what extent this mechanism is conserved across bacteria is unknown.

Outcomes and Expected Impact

We will provide means to guide action both at the source (approval), and in other parts of the water cycle. Standardization of methodology will facilitate possible future inclusion in regulatory systems in Europe and elsewhere. Here, the involvement of stakeholders, particularly regulatory bodies, in the process is important. The maritime sector will receive guidance to improve sustainable transports by a better understanding of potential human health risks associated with antifouling agents (also used in e.g. fish farming). While our ultimate goal is to protect the ability to prevent and treat bacterial infections using antibiotics, the generation of analytical tools, environmental exposure data and effect data for a range of microorganisms will also inform risks for ecological effects.

Data

Generated data will include

1) exposure levels in different matrices,

2) concentrations that are likely to co-select for antibiotic resistance and promote horizontal gene transfer,

3) identification of predominant and novel genetic mechanisms for co-selection, as well as

4) a risk assessment.

Work Packages 

Exposure

1) Prioritize antibacterial biocides to be investigated based on existing databases on sales, uses and detection in aquatic environments

2) Develop stateof-the art chemical analysis protocols for a range of antibacterial biocides, applicable to different sample types, and

3) Generate screening data for the presence and levels of antibacterial biocides in different environmental matrices from a set of different aquatic ecosystems in Europe and Africa

Effects

1) Generating a dose-response matrix for a large number of biocides and bacterial species in order to obtain Predicted No Effect Concentrations (PNECs) for growth that will also be protective against AB resistance co-selection,

2) Directly assesssing co-selection by competition experiments in complex aquatic communities using a subset of biocides, and

3) Quantify the potency of selected biocides to induce horizontal transfer of AB resistance genes via conjugation and transformation.

Mechanisms

1) Uncover the incidence and mechanisms of AB resistance driven by metal-based antifouling agents used in international maritime traffic and marine aquaculture,

2) Providing a first description of the predominant co- and cross-resistance mechanisms in bacterial isolates from aquatic ecosystems in Europe and Africa,

3) Identifying the genetic context and basis for resistance to several biocides using a functional (meta) genomics approach combined with exploration of public genomic data.

Synthesis

1) Incorporating extensive data on selective concentrations and co-selection opportunities into the BacMet database to make it useful for practical risk assessment and management,

2) Performing a preliminary assessment of risks for biocides to promote AB resistance in aquatic environments based on generated exposure and effect data,

3) Producing an evaluation scheme in collaboration with relevant authorities on how resistance risks formally could be incorporated in existing regulatory frameworks.