4 Material und Umwelt
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Antimicrobial resistance (AMR) is a global health problem with the environment being an important compartment for the evolution, selection and transmission of AMR. These processes are impacted by pollution with antibiotics. However, biocides used as disinfectants and material preservatives are major pollutants by far excceding the market for antibiotics in terms of mass. Our work shows that biocides have the potential to affect evolutionary processes towards AMR by increasing the rates of de-novo mutation and conjugation. These effects depend on the species and biocidal substance. Importantly, chlorhexidine and quaternary ammonium compounds (QACs) affect rates of mutation and conjugation at environmentally relevant concentrations in E. coli. Moreover, our results show a connection between the RpoS-mediated general stress and the RecA-linked SOS response with increased rates of mutation and conjugation, but not for all biocides. Furthermore, our work highlights the potential of biocides to contribute to selection and transmission of AMR. We show that the application of biocides, especially QAC disinfectants, leads to the rapid evolution of tolerance (i.e. increased survival) in adaptive laboratory evolution (ALE) experiments. The evolved tolerant strains have a selective advantage in the presence of environmentally-relevant concentrations of antibiotics, which could lead to the stabilization of biocide tolerance in environments where biocides and antibiotics co-occur (e.g. wastewater, animal stables). ALE experiments with biocide tolerant strains indicate a decreased evolvability of resistance to antibiotics. Taken together, our work shows the importance of assessing the contribution of biocides on evolution, selection and transmission of AMR in the environment.
BIOCIDE
(2022)
Antimicrobial surfaces have broad use in multiple settings including touch surfaces in hospitals, implanted devices, or consumer products. Their aim is to support existing hygiene procedures, and to help combat the increasing threat of antimicrobial resistance. However, concerns have been raised over the potential selection pressure exerted by such surfaces, which might drive the evolution and spread of antimicrobial resistance. In my presentation, I will highlight the risks and knowledge gaps associated with resistance on antimicrobial surfaces by different processes including evolution by de novo mutations and horizontal gene transfer, and species sorting of inherently resistant bacteria dispersed onto antimicrobial surfaces. The latter process has the potential to select for antibiotic resistance via cross-resistance between traits that confer resistance to both the antimicrobial surface coating and antibiotics. Conditions in which antibiotics and antimicrobial coatings are present simultaneously (e.g. implants) will lead to more complex interactions that can either result in the selection for or against antibiotic resistance. We mapped these interactions between several antimicrobials and antibiotics on growth and selection of Pseudomonas aeruginosa. We find prevalent physiological (i.e. synergy and antagonism) and evolutionary (i.e. cross-resistance and collateral sensitivity) combination effects. Understanding these interactions opens the door to tailor therapeutic interventions to select against resistance. In additions, we need new methods and translational studies that investigate resistance development to antimicrobial surfaces under realistic conditions. Therefore, I will present recent developments in our lab on the development of such a method based on existing efficacy standards.
Biocides, including disinfectants and antimicrobial surfaces (AMCs), are important to prevent the spread of pathogens and antimicrobial resistant bacteria via surfaces. However, concerns have been raised about the evolution and selection of resistance against disinfectants and AMCs. In turn, resistance against disinfectants and AMCs can be associated to antibiotic resistance due to cross-resistance and co-resistance. We need to understand the mechanisms and risks of disinfectants and AMCs for resistance and cross-resistance evolution to optimize their application and safeguard their long-term efficacy. We used adaptive laboratory evolution (ALE) experiments based on repeated exposure of bacteria to disinfectants. Our results show that repeated disinfection of E. coli with benzalkonium chloride in suspension results in a 2000-fold increase in survival within 5 exposure cycles. Adaption is linked to the initial presence of persister cells highly tolerant to benzalkonium chloride. We used the same approach to develop standardizable ALE experiments to determine resistance evolution to AMCs. The results highlight rapid adaptation of E. coli and P. aeruginosa towards copper surfaces. Moreover, there are multiple situations in the clinic or in the environment in which biocides and antibiotics co-occur and in which combination effects can shape their antimicrobial activity or their selective effects. Our work with P. aeruginosa shows prevalent combination effects of biocides and antibiotics, ranging from synergy to antagonism and resulting in the selection for or against antibiotic resistant strains. The combination effects are dependent on the biofilm mode-of-growth, manifesting in apparent differences in the structural arrangement of antibiotic sensitive and resistant strains in biofilms exposed to combinations. Furthermore, biocides affect rates of mutation and horizontal gene transfer, thereby having a potential facilitating effect on resistance evolution. Taken together, our work shows that the role of biocides as potential drivers of resistance evolution and selection deserves further study and regulative action.