4 Material und Umwelt
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- Corrosion (7)
- Methanogens (6)
- Biocides (5)
- Biofilm (4)
- Biofilms (3)
- Environmental Simulation (3)
- Horizontal gene transfer HGT (3)
- MIC (3)
- Microbiology (3)
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Organisationseinheit der BAM
- 4.1 Biologische Materialschädigung und Referenzorganismen (23) (entfernen)
Microbiologically influence corrosion (MIC) has become a big concern due the increased usage of different metals by our society. Microorganisms can use metal as an electron donor, causing unpredictable but serious damages. Nowadays it is known that besides sulfate reducing bacteria (SRB), other microorganisms including acetogens, iron oxidizers and methanogens can also induce MIC. Current studies related to methanogen-induced MIC (MI-MIC) mainly focused on environmental isolates from the oil and gas industry (e.g. Methanococcus maripaludis) with industrial materials e.g. iron. However, MI-MIC can occur in many other environments as well, including the oral cavity. Methanobrevibacter oralis is a methanogen isolated from the human oral cavity and was found more frequently in patients suffering from peri-implantitis/periodontitis. Titanium-implants removed from those patients have also showed clear signs of corrosion. The aim of our study is to establish and analyze corrosion potentials of dental metals (e.g. titanium) by oral methanogens. Periodontal pockets samples from patients suffering from periodontitis/peri-implantitis were taken for methanogenic and SRB enrichments. Stainless steel, pure titanium or Ti-6Al-4V alloy was used for corrosion studies. Corrosion rates and methane production were measured using weight-loss method and gas chromatography, respectively. Metal surfaces were visualized with scanning electron microscopy. Microbial communities in the dental pockets of healthy people and patients will be compared using 16S rRNA amplicon sequencing. Overall, this is the first study investigating the susceptibility of different dental implant materials to corrosion using human-related Archaea. The outcomes of this study can be further explored for a variety of clinical applications.
The halophilic bacterium Halomonas elongata can tolerate salt concentrations above 10% NaCl and uses the accumulation of the compatible solute ectoine as a major osmoregulatory mechanism. Ectoine can be accumalted inside the cell through import from the medium or de novo synthesis and establishes an osmotic equilibrium with the surrounding1. Ectoine also protects proteins from the effects of freezing, drying and high temperatures4 and DNA from ionizing radiation2. These features make ectoine a valuable compound for cosmetics and medical devices.
H. elongata was originally isolated from a solar salt facility, where it thrives under high salt concentrations. It was found that marine prokaryotes, which are exposed to high oxidative stress in their environment, vary glycolytic strategies5. A variation in the use of the glucose metabolic pathways is also assumed for H. elongata.
Surface characterisation of biofilms by nearambient pressure X-ray photoelectron spectroscopy
(2018)
The XPS information depth of approximately 10 nm is in the same size range as the outer membrane of the gram-negative bacteria, which makes XPS a suitable tool for determining the elemental composition of the bacterial surface and monitor changes caused by outer stress like dehydration or exposure to antimicrobials. However, bacteria are inherently in a hydrated state, and therefore only compatible to ultra-high vacuum after extensive sample preparation, which may degrade the sample constituents. This issue is addressed by the development of near-ambient pressure (NAP)-XPS, which enables bacteria and biofilms to be characterised in their native wet state. Artificial biofilms, bacteria and biofilms of Escherichia coli have been characterised with the laboratory NAP-XPS instrument EnviroESCA from SPECS GmbH, at pressures ranging from high vacuum to 12 mbar, and in both humid and dry environment. By studying biological samples in their native wet state, new insight about composition and transport of drugs through cell membranes and the extracellular polymeric substance (EPS) of biofilms can be obtained.
Background Bacterial biofilms are regarded as the most common cause of chronic infections and are often associated with medical devices, such as implants and catheters. Bacteria growing in biofilms produce a protective, extracellular matrix, which enables them to tolerate much higher antimicrobial concentrations than free-living bacteria and survive long enough to acquire antimicrobial resistance. Preventive and therapeutic strategies against biofilm infections in clinical settings commonly involve the application of multiple antimicrobials: biocidal coatings on the biomaterials and systemically administered antibiotics. This frequent practice harbors the risk of the development of cross-resistance via shared resistance mechanisms between antimicrobials used in material coatings and administered antibiotics.
Aim Our goal is to determine how bacteria adapt to antimicrobials during biofilm formation on surfaces coated with antimicrobials and how population dynamics within biofilms affect the transmission of resistance mutations. Specifically, we want to identify antimicrobial-antibiotic-combinations that select for and against antibiotic resistance in biofilms by following the population dynamics of resistant and susceptible strains in competition assays on a single cell level.
Methodology To study the effect of antimicrobial-antibiotic exposure on resistance development and population dynamics on bacterial biofilms in a multidrug environment, we will grow Pseudomonas aeruginosa on glass surfaces with and without antimicrobial coatings and expose them to antibiotics. First, we will screen in vitro for combinations of antibiotics and antimicrobials that select for and against antibiotic resistance. Second, effective combinations will be chosen for in-depth investigations during bacterial adhesion and of mature biofilms of resistant and susceptible genotypes. Third, based on the outcome of the screen and the obtained mechanistic understanding we will choose a clinical example in which we study the relevance of our findings in biofilms grown in vivo.
Relevance Studying the biointerfacial interactions between bacterial biofilms and medical devices in terms of population dynamics as well as on single cell level during multidrug selection will help us understand how drug resistance develops and spreads in persistent biofilm infections. Based on our findings we aim to provide clinical recommendations for improved administration of antibiotics/antimicrobials in combination with medical device materials in order to mitigate against biofilm associated antimicrobial resistance.
Background Bacterial biofilms are regarded as the most common cause of chronic infections and are often associated with medical devices, such as implants and catheters. Bacteria growing in biofilms produce a protective, extracellular matrix, which enables them to tolerate much higher antimicrobial concentrations than free-living bacteria and survive long enough to acquire antimicrobial resistance. Preventive and therapeutic strategies against biofilm infections in clinical settings commonly involve the application of multiple antimicrobials: biocidal coatings on the biomaterials and systemically administered antibiotics. This frequent practice harbors the risk of the development of cross-resistance via shared resistance mechanisms between antimicrobials used in material coatings and administered antibiotics.
Aim Our goal is to determine how bacteria adapt to antimicrobials during biofilm formation on surfaces coated with antimicrobials, how antimicrobial resistance mutations are acquired and evolve within mature biofilms, and how population dynamics within biofilms affect the transmission of resistance mutations. Specifically, we want to identify antimicrobial-antibiotic-combinations that select for and against antibiotic resistance in biofilms by following the population dynamics of resistant and susceptible strains in competition assays.
Methodology We will grow biofilms of Pseudomonas aeruginosa on glass surfaces with and without antimicrobial coatings and expose them to antibiotics. Then we will track their physiological properties, evolutionary adaptations, and population dynamics. First, we will screen in vitro for combinations of antibiotics and antimicrobials that select for and against antibiotic resistance. Second, effective combinations will be chosen for in-depth investigations during bacterial adhesion and of mature biofilms of resistant and susceptible genotypes. Third, based on the outcome of the screen and the obtained mechanistic understanding we will choose a clinical example in which we study the relevance of our findings in biofilms grown in vivo.
Relevance Studying the biointerfacial interactions between bacterial biofilms and medical devices in terms of population dynamics as well as on single cell level during multidrug selection will help us understand how drug resistance develops and spreads in persistent biofilm infections. Based on our findings we aim to provide clinical recommendations for improved administration of antibiotics/antimicrobials in combination with medical device materials in order to mitigate against biofilm associated antimicrobial resistance.
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.
Antimicrobial resistance is a major threat to human health. The prevalence of multi-drug resistant (MDR) bacteria is predicted to increase in the future requiring robust control strategies. One cornerstone to prevent the spread of MDR bacteria in clinical settings is the application of disinfectants to improve hygiene standards. However, bacteria can evolve resistance to disinfectants, which in turn can confer cross-resistance to antibiotics. Additionally, clonal bacterial populations can display phenotypic heterogeneity with respect to the tolerance of antibiotic stress leading to a prolonged survival of a sub-population; this phenomenon is termed persistence. Persistence to antibiotics is an evolvable trait and can serve as a stepping stone for the evolution of genetically encoded resistance. Until now, there is a lack of systematic studies that investigate if bacterial populations establish persister subpopulations that tolerate disinfectant stress longer than the majority of the population. Our results in E. coli indicate that persistence is a bacterial survival strategy against benzalkonium chloride, a widely used disinfectant.
In future experiments, we will investigate the evolution of persistence in the face of fluctuating exposure to disinfectants and whether persistence facilitates resistance against disinfectants. Lastly, we will test how tolerance and resistance against disinfectants affects susceptibility against antibiotics.
Microbially influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) which act upon the metal by the reactiveness of hydrogen sulfide, and by withdrawal of the available electrons (Fe → Fe²⁺ + 2e⁻ ; E° = 0.47 V) in electrical contact through surface attachment. Also methanogenic archaea are supposed to cause MIC. Because they do not produce hydrogen sulfide, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood. Precipitation of siderite (4Fe + 5HCO₃⁻ + 5H⁺ → 4FeCO₃ + CH₄ + 3H₂O) can lead to an insulating layer on the metal surface and lower the corrosion rate. Still, the extent of FeCO₃ precipitation may be significantly influenced by environmental conditions such as pH and advective processes.
To investigate the corrosive potential of methanogens, we studied strains isolated from marine sediments (Methanococcus maripaludis 14266, 2067, Methanobacterium-affiliated strain IM1), crude oil tanks (Methanococcus maripaludis Mic1c10, KA1) and the oral cavity (Methanobrevibacter oralis) in a closed (batch) culture, and in a sand-packed flow-through cell with pH control and simulation of a fluctuating environment. Results indicate that the rates of iron corrosion due to coupled methanogenesis (up to 0.3 mm/yr) are comparable to that caused by SRM. Surface analyses of the metal showed severe pitting. Such knowledge and deeper understanding also from an electrokinetic point of view may not only provide further models in microbial electrophysiology, but also contribute to mitigation strategies in MIC.
Microbially influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) which act upon the metal by the reactiveness of hydrogen sulfide, and by withdrawal of the available electrons in electrical contact with the metal. Methanogenic archaea are supposed to cause MIC. Because they do not produce hydrogen sulfide, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood. Precipitation of siderite (4Fe + 5HCO3 + 5H+ 4FeCO3 + CH4 + 3H2O) can lead to an insulating layer on the metal surface and lower the corrosion rate. Still, the extent of FeCO3 precipitation may be significantly influenced by environmental conditions such as pH and advective processes.