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A fundamental question in ecology is how biodiversity affects ecosystem function. Biodiversity is commonly estimated based on genetic variation. We investigated a new approach that defines and measures biodiversity in complex microbial communities. We used the variation in multiple functionally-relevant, phenotypic traits measured in parallel in single cells as a metric for microbial phenotypic diversity. We studied phenotypic diversity and ecosystem functioning throughout different photosynthetic layers dominated by divergent microbial communities in the gradient of Lago di Cadagno. We determined genetic diversity by 16S and 18S amplicon sequencing and bulk ecosystem functioning (photosynthesis). In addition, we determined phenotypic diversity using single-cell technologies such as nanometer-scale secondary ion mass spectrometry (NanoSIMS) correlated with confocal laser scanning microscopy (CLSM) and scanning flow-cytometry. We measured functional trait variation between individuals in 13CO2 fixation, 15NH4+ uptake, and variation in physio-morphological cell traits, such as cell size, shape, and auto-fluorescence for various pigments related to photosynthesis. We used the distances between individuals in a multidimensional trait space to derive phenotypic trait-based diversity indices, such as trait richness, trait evenness, and trait divergence. We find that phenotypic trait divergence associates with ecosystem functioning, whereas genetic diversity does not. Including activity-based, single-cell phenotypic measurements with NanoSIMS provided an additional accuracy to the trait-based diversity assessment and allowed us to formulate hypotheses on the mechanisms that shape the correlation between phenotypic diversity and eco-system function. Together, our results show that phenotypic diversity is a meaningful concept to measure microbial biodiversity and associate it with ecosystem functioning.
A fundamental question in ecology is how biodiversity affects ecosystem function. Biodiversity is commonly estimated based on genetic variation. We investigated a new approach that defines and measures biodiversity in complex microbial communities. We used the variation in multiple functionally-relevant, phenotypic traits measured in parallel in single cells as a metric for microbial phenotypic diversity. We studied phenotypic diversity and ecosystem functioning throughout different photosynthetic layers dominated by divergent microbial communities in the gradient of Lago di Cadagno. We determined genetic diversity by 16S and 18S amplicon sequencing and bulk ecosystem functioning (photosynthesis). In addition, we determined phenotypic diversity using single-cell technologies such as nanometer-scale secondary ion mass spectrometry (NanoSIMS) correlated with confocal laser scanning microscopy (CLSM) and scanning flow-cytometry. We measured functional trait variation between individuals in 13CO2 fixation, 15NH4+ uptake, and variation in physio-morphological cell traits, such as cell size, shape, and auto-fluorescence for various pigments related to photosynthesis. We used the distances between individuals in a multidimensional trait space to derive phenotypic trait-based diversity indices, such as trait richness, trait evenness, and trait divergence. We find that phenotypic trait divergence associates with ecosystem functioning, whereas genetic diversity does not. Including activity-based, single-cell phenotypic measurements with NanoSIMS provided an additional accuracy to the trait-based diversity assessment and allowed us to formulate hypotheses on the mechanisms that shape the correlation between phenotypic diversity and eco-system function. Together, our results show that phenotypic diversity is a meaningful concept to measure microbial biodiversity and associate it with ecosystem functioning.
Antimicrobial resistance (AMR) is a global health problem. It is well known that antibiotics can drive evolutionary processes that underlie antimicrobial resistance (AMR) evolution and spread in clinical and environmental settings. In contrast, less is known about the effects of antimicrobial substances that are used as biocides (i.e. disinfectants and preservatives) on AMR evolution and spread. Biocides are present in various settings, interacting with diverse microbial communities. Therefore, it is crucial to evaluate their role in the evolution and dissemination of antimicrobial resistance. Biocides occur in a wide range of concentrations in various environmental settings. By examining how the various concentrations affect selection mechanisms, we gain insights into potential developments related to antimicrobial resistance. The aim of this PhD thesis is to investigate the effects of biocides on processes underlying resistance evolution. Specifically, the work focused on key mechanisms for resistance spread, resistance evolution, and the effect of selection pressures on evolved resistance mechanisms. The thesis is structured around three major objectives: (i) to determine the effect of biocides on the evolution of resistance by affecting the rate of occurrence of de novo mutations, (ii) to determine the effect of biocides on the spread of resistance genes by modifying the rate of horizontal gene transfer (HGT) processes, and (iii) to investigate the selective drivers of the emergence of antimicrobial resistance in adaptive laboratory evolution (ALE) experiments. De-novo mutations are spontaneous mutations that occur at a certain rate in microorganisms. The effect of biocides at subinhibitory environmentally relevant concentrations on the mutation rate in Acinetobacer baylyi, Bacillus subtilis and Escherichia coli was assessed with the fluctuation assay. The results showed that biocides affected mutation rates in a species and substance dependent matter. The bisbiguanide chlorhexidine digluconate, the quaternary ammonium compound didecyldimethylammonium chloride, the metal copper, the pyrethroid-insecticide permethrin, and the azole-fungicide propiconazole increase mutation rates in E. coli, whereas no increases were identified for B. subtilis and A. baylyi. Horizontal gene transfer refers to diverse mechanisms that mediate the transfer of mobile genetic elements between microorganisms. This work focused on conjugation and transformation. Conjugation is a process whereby a conjugative plasmid is transferred from a donor cell to a recipient cell. Transformation is a process whereby exogenous donor DNA is taken up into a recipient cell and integrated into the recipient’s’ genome. The effects of subinhibitory environmentally relevant biocide concentrations on the conjugation rate of E. coli and the transformation rate of the naturally competent organisms A. baylyi in were assessed. The results showed that benzalkonium chloride (BAC), chlorhexidine and permethrin increased conjugation in E. coli, while none of the biocides increased transformation rates in A. baylyi. To further understand the molecular mechanisms underlying the effects on mutation and conjugation rates, I investigated the induction of the RpoS-mediated general stress and the RecA-linked SOS response upon biocide exposure. The results show a link between the general stress and the SOS response with increased rates of mutation and conjugation, but not for all biocides. One major approach to study the evolutionary response of bacteria to antimicrobials are ALE experiments with growth at subinhibitory concentrations linked to serial subculturing over many generations. Such experiments have been used to study resistance evolution to antibiotics and biocides. However, previous work showed that adaptation to biocide stress may be mediated by different evolutionary drivers. Here, I investigated the contributions of evolution for increased survival as opposed to improved growth in ALE experiments with E. coli exposed to subinhibitory BAC concentrations. Two distinct evolutionary treatments selecting for survival only or survival and growth led to specific evolutionary adaptations apparent in the phenotypes and genotypes of the evolved populations. Populations growing in the presence of BAC evolved increased fitness in the presence of BAC associated with higher resistance to BAC and cross-resistance to antibiotics, while this was not the case for populations evolving for increased survival only. Genotypic characterization by whole genome sequencing of the evolved populations revealed parallelism in mutated genes among replicate populations and distinct differences across treatments. Treatments selecting for survival and growth showed mutations in stress response related genes (hslO and tufA), while selection for survival led to mutations in genes for metabolic regulation (cyaA) and cellular structure (flagella fliJ). In summary, this thesis shows that biocides affect AMR evolution and emphasizes the importance of understanding of how biocides impact the molecular and evolutionary process that underlie AMR evolution.
Biocides are in contact with soils through direct application and passive leaching from protected materials. Consequently, soil microorganisms are exposed to biocides even though they are not their primary targets. Soil is a large reservoir of microbial diversity and has been hypothesized to be a crucial factor for the evolution and spread of antimicrobial resistance.
Currently, there is little knowledge on how biocides used to protect materials affect the evolution and spread of resistance. Thus, our aim is to investigate the risk for the evolution of biocide resistance and cross-resistance to antibiotics. In addition, we aim to elucidate the affect of biocides on the spread of resistance via horizontal gene transfer (HGT).
In adaptive laboratory evolution experiments we cultured selected model soil microorganism with representative biocides under selection regimes with increasing and stable biocide concentrations followed by antibiotic and biocide cross-resistance determination. Moreover, we investigate if the selected biocides affect the rates of de novo mutations and HGT of plasmids that carry resistance genes among soil microorganism.
Our results show only small increases of biocide resistance during serial transfers under increasing biocide concentrations. One reason for this might be the narrow selective window for biocide resistance due to steep dose-response relationships. Furthermore, our results indicate that a stable low-level biocide regime did not select for high level cross-resistance to antibiotics and other biocides.
Moreover, material preservatives affected the rates of HGT via conjugation and the mutation rates at sub-inhibitory concentrations. The results will enable future risk assessment regarding resistance evolution for biocides used as material preservatives.
Biocides used as material preservatives are in contact with various environments during direct application or passive leaching from protected materials [1]. Antimicrobial resistance (AMR) is a global health problem and the environment is an important compartment for the evolution and transmission of AMR [2,3]. Soil is an environment with a large reservoir of natural microbial communities and antimicrobial resistance (AMR) genes. Those natural microbial communities are frequently exposed to biocides used as material preservatives. Previous studies have shown that antibiotics, metals and pesticides affect the underlying processes of resistance evolution and spread; namely de novo mutagenesis and horizontal gene transfer by conjugation and transformation in microbial communities. However, it is unknown if active substances used in material preservatives are involved in these processes. We show that biocides used as material preservatives affect rates of mutation and conjugation in microorganism in a species- and substance-dependent manner, while rates of transformation are not directly affected. Our data highlights the importance of assessing the contribution of material preservatives on AMR evolution and spread in the environment.
Question
Disinfectants and antimicrobial surfaces (AMCs) are important tools to prevent the spread of pathogens and antimicrobial resistant bacteria. However, concerns have been raised about the possibility for 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 - a single mechanism conferring resistance to a disinfectant and an antibiotic- and co-resistance - two distinct mechanisms physically linked on e.g. a plasmid. The risk for resistance and cross-resistance during use of biocides (including disinfectants and AMCs) must be evaluated during authorization according to the EU biocidal product regulation. However, to date there is a lack of standardized methods that support risk assessment during the authorization process.
Methods
We used adaptive laboratory evolution (ALE) experiments which are based on repeated exposure of bacteria to disinfectants or AMCs. The experiments are followed by phenotypic (antimicrobial susceptibility testing) and genotypic (whole genome sequencing) characterization of the evolved strains. The basic idea of these experiments is to expose bacteria to lethal conditions and select for mutants with increased survival. This approach is fundamentally different to other ALE experiments, which commonly select for increased growth at subinhibitory concentrations. However, selection for increased survival represents a selective pressure that more realistically reflects selection under in-use conditions of disinfectants and AMCs.
Results
First, we studied adaptation of E. coli during repeated disinfection with benzalkonium chloride in a suspension assay. The experiments showed a 2000-fold increase in survival within 5 exposure cycles. The adaptive changes are linked to highly parallel mutations in genes related to lipid A biosynthesis, less negative cell surface charge, reduced growth rate and increased competitive ability in the presence of certain antibiotics. We use the same approach to develop standardizable ALE experiments based upon accepted standards that are used to determine the efficacy of disinfectants (EN 13697) and antimicrobial surfaces (ISO 22196). The results highlight pronounced adaptation of different test strains towards surface disinfection (benzalkonium chloride and isopropanol) and AMCs (copper).
Conclusion
Bacteria can adapt with increased survival towards lethal stress imposed by disinfectants and AMCs. The adaptive ability of bacteria to disinfectants and AMCs can be determined in a standardized manner.
Biocides used as material preservatives are in contact with various environments during direct application or passive leaching from protected materials. Antimicrobial resistance (AMR) is a global health problem and the environment is an important compartment for the evolution and transmission of AMR. Soil is an environment with a large reservoir of natural microbial communities and antimicrobial resistance (AMR) genes. Those natural microbial communities are frequently exposed to biocides used as material preservatives. Previous studies have shown that antibiotics, metals and pesticides affect the underlying processes of resistance evolution and spread; namely de novo mutagenesis and horizontal gene transfer by conjugation and transformation in microbial communities. However, it is unknown if active substances used in material preservatives are involved in these processes. We show that biocides used as material preservatives affect rates of mutation and conjugation in microorganism in a species- and substance-dependent manner, while rates of transformation are not directly affected. Our data highlights the importance of assessing the contribution of material preservatives on AMR evolution and spread in the environment.
Biocides used as material preservatives are in contact with various environments during direct application or passive leaching from protected materials. Antimicrobial resistance (AMR) is a global health problem and the environment is an important compartment for the evolution and transmission of AMR. Soil is an environment with a large reservoir of natural microbial communities and antimicrobial resistance (AMR) genes. Those natural microbial communities are frequently exposed to biocides used as material preservatives. Previous studies have shown that antibiotics, metals and pesticides affect the underlying processes of resistance evolution and spread; namely de novo mutagenesis and horizontal gene transfer by conjugation and transformation in microbial communities. However, it is unknown if active substances used in material preservatives are involved in these processes. We show that biocides used as material preservatives affect rates of mutation and conjugation in microorganism in a species- and substance-dependent manner, while rates of transformation are not directly affected. Our data highlights the importance of assessing the contribution of material preservatives on AMR evolution and spread in the environment.
Antimicrobial resistance (AMR) is an important global health problem. The environment has been regocnized as an improtant compartment for the occurance, evolution and transmission of AMR. Biocides used as material preservatives are in contact with the environment and natural microbial communities through direct application and passive leaching from protected materials. It has been shown that environmental contaminants, such as antibiotics, metals and pesticides, can affect resistance evolution and spread by modifying the underlying processes of de novo mutagenesis, horizontal gene transfer and selection. However, it is unknown if material preservatives are involved in these processes and thereby can also drive AMR in the environment. Here, we investigate the effect of material preservatives on rates of de novo mutation and horizontal gene transfer (HGT) in Escherichia coli and the model soil microorganisms Acinetobacter baylyi and Bacillus subtilis. To this end, we determined the effects of material preservatives on the mutation rates and HGT with the Luria-Delbrück fluctuation assay and a conjugation assay with the broad host-range plasmid pKJK5 and a transformation assay. Our data shows that the quaternary ammonium compound DDAC, copper, the pyrethroid insecticide permethrin and the azole fungicide propiconazole significantly increase mutation rates in E. coli, whereas A. baylyi and B. subtilis are not significantly affected. Moreover, we show that the carbamate IPBC and the insecticide permethrin affect HGT in a concentration dependent manner. Investigations with reporter strains for bacterial stress response pathways show that induction of the general stress response (rpoS) and components of the SOS response (recA) underlie the effects of most biocides on mutation rates and HGT. Taken together, our data is important for assessing the contribution of biocides on AMR evolution and spread in the environment.
Soil microbes are exposed to different environmental stressors originating from various sources. Biocides used as material preservatives can represent environmental stressors since they are in direct contact with the environment including soil. Microorganism in soils can adapt to stress by different mechanisms; for example, by transferring mobile genetic elements via horizontal gene transfer (HGT). Here, we hypothesize that material preservatives can cause increased frequencies of HGT (i.e. altered community permissiveness) facilitating microbial community adaptation to stress. Furthermore, we hypothesize that soil microbial communities are primed by biocide exposure facilitating the response to different types of stresses. We will incubate soil mesocosms with selected biocides to investigate if these compounds promote HGT of plasmids that carry resistance genes in soil microbial communities. Subsequently, we will prime the soil microbial community with sub-inhibitory concentrations of biocides followed by exposure to toxic biocide concentrations or other types of common environmental stresses including metals, antibiotics, and salt. Using suitable control experiments, a shift in the functional response of the primed as compared to the non-primed community would indicate that biocides prime microbial communities via HGT. Together these results will elucidate the effect of biocides on HGT-mediated adaptation to environmental stressors in soil microbial communities.
Soil microbes are exposed to different environmental stressors originating from various sources. Biocides used as material preservatives can represent environmental stressors since they are in direct contact with the environment including soil. Microorganism in soils can adapt to stress by different mechanisms; for example, by transferring mobile genetic elements via horizontal gene transfer (HGT). Here, we hypothesize that material preservatives can cause increased frequencies of HGT (i.e. altered community permissiveness) facilitating microbial community adaptation to stress. Furthermore, we hypothesize that soil microbial communities are primed by biocide exposure facilitating the response to different types of stresses. We will incubate soil mesocosms with selected biocides to investigate if these compounds promote HGT of plasmids that carry resistance genes in soil microbial communities. Subsequently, we will prime the soil microbial community with sub-inhibitory concentrations of biocides followed by exposure to toxic biocide concentrations or other types of common environmental stresses including metals, antibiotics, and salt. Using suitable control experiments, a shift in the functional response of the primed as compared to the non-primed community would indicate that biocides prime microbial communities via HGT. Together these results will elucidate the effect of biocides on HGT-mediated adaptation to environmental stressors in soil microbial communities.
Soil microbes are exposed to different environmental stressors originating from various sources. Biocides used as material preservatives can represent environmental stressors since they are in direct contact with the environment including soil. Microorganism in soils can adapt to stress by different mechanisms; for example, by the evolution of resistance by de novo mutations or acquisition of resistance genes via horizontal gene transfer (HGT). Here, we hypothesize that material preservatives could enhance the evolution of biocide resistance enabling the potential for cross-resistance to antibiotics. Furthermore, we hypothesize that material preservatives can cause increased frequencies of HGT (i.e. altered community permissiveness) facilitating microbial community adaptation to stress. We will culture soil microorganism with increasing concentrations of selected biocides followed by antibiotic susceptibility determination. Moreover, we will incubate soil mesocosms with selected biocides to investigate if these compounds promote HGT of plasmids that carry resistance genes in soil microbial communities. Together these results will elucidate the potential for the evolution of biocide resistance and cross-resistance to antibiotics as well as the effect of biocides on adaptation to environmental stressors in soil microbial communities.
Questions:
Biocides are in contact with soils through direct application and passive leaching from protected materials. Consequently, soil microorganisms are exposed to toxic biocides even though they are not their primary targets. Soil is a large reservoir of microbial diversity and has been hypothesized to be a crucial factor for the evolution and spread of antimicrobial resistance. Currently, there is little knowledge on how biocides used to protect materials affect the evolution and spread of resistance. Thus, our aim is to investigate the risk for the evolution of biocide resistance and cross-resistance to antibiotics. In addition, we aim to elucidate the affect of biocides on the spread of resistance via horizontal gene transfer (HGT).
Methods:
In laboratory evolution experiments we culture selected model soil microorganism with representative biocides followed by antibiotic cross-resistance determination and genome sequencing. Moreover, we investigate if the selected biocides affect the HGT frequency of plasmids that carry resistance genes among soil microorganism and the consequences for survival of the affected populations.
Results:
Our initial results show only small increases of biocide resistance during serial transfers in the presence of biocides. One reason for this might be the narrow selective window for biocide resistance due to steep dose-response relationships. Furthermore, we will present results from ongoing experiments on the effects of material preservatives on HGT frequencies facilitating microbial community adaptation to stress.
Conclusions:
The results will enable future risk assessment regarding resistance evolution for biocides used as material preservatives.
Question:
Biocides are in contact with soils through direct application and passive leaching from protected materials. Consequently, soil microorganisms are exposed to toxic biocides even though they are not their primary targets. Soil is a large reservoir of microbial diversity and has been hypothesized to be a crucial factor for the evolution and spread of antimicrobial resistance. Currently, there is little knowledge on how biocides used to protect materials affect the evolution and spread of resistance. Thus, our aim is to investigate the risk for the evolution of biocide resistance and cross-resistance to antibiotics. In addition, we aim to elucidate the affect of biocides on the spread of resistance via horizontal gene transfer (HGT).
Methods:
In laboratory evolution experiments we culture selected model soil microorganism with representative biocides followed by antibiotic cross-resistance determination and genome sequencing. Moreover, we investigate if the selected biocides affect the HGT frequency of plasmids that carry resistance genes among soil microorganism and the consequences for survival of the affected populations.
Results:
Our initial results show only small increases of biocide resistance during serial transfers in the presence of biocides. One reason for this might be the narrow selective window for biocide resistance due to steep dose-response relationships. Furthermore, we will present results from ongoing experiments on the effects of material preservatives on HGT frequencies facilitating microbial community adaptation to stress.
Conclusions:
The results will enable future risk assessment regarding resistance evolution for biocides used as material preservatives.
Question:
Biocides are in contact with soils through direct application and passive leaching from protected materials. Consequently, soil microorganisms are exposed to toxic biocides even though they are not their primary targets. Soil is a large reservoir of microbial diversity and has been hypothesized to be a crucial factor for the evolution and spread of antimicrobial resistance. Currently, there is little knowledge on how biocides used to protect materials affect the evolution and spread of resistance. Thus, our aim is to investigate the risk for the evolution of biocide resistance and cross-resistance to antibiotics. In addition, we aim to elucidate the affect of biocides on the spread of resistance via horizontal gene transfer (HGT).
Methods:
In laboratory evolution experiments we culture selected model soil microorganism with representative biocides followed by antibiotic cross-resistance determination and genome sequencing. Moreover, we investigate if the selected biocides affect the HGT frequency of plasmids that carry resistance genes among soil microorganism and the consequences for survival of the affected populations.
Results:
Our initial results show only small increases of biocide resistance during serial transfers in the presence of biocides. One reason for this might be the narrow selective window for biocide resistance due to steep dose-response relationships. Furthermore, we will present results from ongoing experiments on the effects of material preservatives on HGT frequencies facilitating microbial community adaptation to stress.
Conclusions:
The results will enable future risk assessment regarding resistance evolution for biocides used as material preservatives.
Using nanofiber-like cell appendages, secreted proteins and sugars, bacteria can establish initial surface contact followed by irreversible adhesion and the formation of multicellular biofilms, often with enhanced resistance towards antimicrobial treatment and established cleaning procedures. On e.g. medical implants, in water supply networks or food-processing industry, biofilms can be a fertile source of bacterial pathogens and are repeatedly associated with persisting, nosocomial and foodborne infections. Nowadays, the emergence of resistances because of extensive usage of antibiotics and biocides in medicine, agriculture and private households have become one of the most important medical challenges with considerable economic consequences. In addition, aggravated biofilm eradication and prolonged cell-surface interaction can lead to increased biodeterioration and undesired modification of industrial and medical surface materials. Various strategies are currently developed, tested, and improved to realize anti-bacterial surface properties through surface functionalization steps avoiding antibiotics.
In this study, contact-less and aseptic large-area short or ultrashort laser processing is employed to generate different surface structures in the nanometer- to micrometer-scale on technical materials such as titanium-alloy and polyethylene terephthalate (PET). The laser processed surfaces were subjected to bacterial colonization studies with Escherichia coli test strains and analyzed with reflected-light and epi-fluorescence microscopy. Depending on the investigated surfaces, different bacterial adhesion patterns were found, ranging from bacterial-repellent to bacterial-attractant effects. The results suggest an influence of size, shape and cell appendages of the bacteria and – above all – the laser-processed nanostructure of the surface itself, emphasizing the potential of laser-processing as a versatile tool to control bacterial surface adhesion.
Bacterial biofilms are multicellular communities adhering to surfaces and embedded in a self-produced extracellular matrix. Due to physiological adaptations and the protective biofilm matrix itself, biofilm cells show enhanced resistance towards antimicrobial treatment. In medical and industrial settings, biofilms on e.g. for implants or for surfaces in food-processing industry can be a fertile source of bacterial pathogens and are repeatedly associated with persisting, nosocomial and foodborne infections. As extensive usage of antibiotics and biocides can lead to the emergence of resistances, various strategies are currently developed, tested and improved to realize anti-bacterial surface properties through surface functionalization steps avoiding antibiotics. In this study, contact-less and aseptic large-area ultrashort laser scan processing is employed to generate different surface structures in the nanometer- to micrometer-scale on technical materials, i.e. titanium-alloy, steel, and polymer. The processed surfaces were characterized by optical and scanning electron microscopy and subjected to bacterial colonization studies with Escherichia coli test strains. For each material, biofilm results of the fs-laser treated surfaces are compared to that obtained on polished (non-irradiated) surfaces as a reference. Depending on the investigated surfaces, different bacterial adhesion patterns were found, suggesting an influence of geometrical size, shape and cell appendages of the bacteria and – above all – the laser-processed nanostructure of the surface itself.
Using nanofiber-like cell appendages, secreted proteins and sugars, bacteria can establish initial surface contact followed by irreversible adhesion and the formation of multicellular biofilms. Here, the stabilizing extracellular biofilm matrix together with physiological changes on the single cell level leads to an increased resilience towards harsh environmental conditions, antimicrobials, the host immune response and established cleaning procedures. Persistent microbial adhesion on e.g., medical implants, in water supply networks or food-processing industry is often associated with chronic inflammation, nosocomial and foodborne infections, enhanced biofouling and product contamination. To prevent persistent microbial colonization, antibacterial surface strategies often target the initial steps of biofilm formation and impede adhesion of single cells before a mature biofilm is being formed. While chemical coatings have been widely used, their restricted biocompatibility for eukaryotic cells and attenuated antibacterial-effects due to compound release limit their areas of application and alternative strategies focus on modified surfaces topographies to impede bacterial adhesion. In this work, we used ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns) to generate laser-induced periodic surface structures (LIPSS) with different submicrometric periods ranging from ~210 to ~610 nm on commercial poly(ethylene terephthalate) (PET) foils. Following structurally and chemically analyses, PET samples were subjected to bacterial colonization studies with Escherichia coli TG1, a bacterial test strain with a strong biofilm formation capacity due to the formation of nanofiber-like cell-appendages (pili). Bacterial adhesion tests revealed that E. coli repellence decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the importance of extracellular appendages in the bacterial repellence observed here, thus, pointing out new antibiotics-free strategies for antibacterial surfaces by impeding nanofiber-mediated bacterial adhesion.
Anoxische Objektbehandlungen gegen Schädlingsbefall stellen eine besonders materialverträgliche und umweltschonende Alternative zu chemischen Bekämpfungsverfahren dar. Die Wirksamkeit hängt jedoch von der Dauer, dem Restsauerstoffgehalt sowie der Temperatur und Feuchtigkeit ab. Unterschiedliche Arten von Schadinsekten sind verschieden tolerant gegenüber sauerstoffarmen Bedingungen. Insbesondere bei Behandlungsbedingungen von unter 24° C und mehr als 0,5 % Restsauerstoffgehalt stößt das Verfahren an die Grenze der Zuverlässigkeit. In Versuchsreihen unter standardisierten Bedingungen erwiesen sich insgesamt 12 von 34 im Projekt untersuchte Insektenarten hierbei als widerstandsfähig. Davon als besonders tolerante Arten sind Hylotrupes bajulus, Lasioderma serricorne, Trogoderma parabile und Mezium affine zu nennen.
Mit dem entwickelten UWB-Sensoriksystem können durch elektromagnetische Wellen Bewegungen von Schädlingen innerhalb geschlossener Holzobjekte berührungslos erfasst werden. Voraussetzung für die eindeutige Detektion der Schädlingsaktivität ist neben der digitalen Signalverarbeitung zur Filterung und Extraktion des Nutzsignals, die genügend hohe Eindringtiefe, die ausreichend ist, wenn Schädlingsvorkommen häufig dicht unter der Holzoberfläche gelegen sind. Die Versuchsergebnisse haben gezeigt, dass bereits eine einzelne Trockenholztermite der Art Incisitermes marginipennis hinter einer 5 cm dicken Holzplatte aufgespürt werden kann. Somit erscheint das Messsystem potentiell für die Erfolgskontrolle einer Anoxia-Behandlung an Museumsgütern geeignet.
Bacteria are ubiquitous and colonize all types of surfaces, including those in close proximity to humans, such as skin, food, and everyday objects. This raises the question of whether their presence represents a problem to be mitigated or a potential source of benefit to be harnessed, thereby stimulating scientific inquiry into the role of surface-associated bacteria in diverse domains ranging fromhuman health to industrial biotechnology. Aim: The objective of this project is to explore the impact of modifying surface topography on bacterial adhesion behavior. By manipulating the physical characteristics of the substrate, the attachment and detachment dynamics of bacteria can potentially be modified, leading to novel strategies for controlling bacterial colonization in various applications, such as medical devices. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were tested on LIPSS-covered Fused Silica samples.