Quartz tuning fork studies on the surface properties of Pseudomonas aeruginosa during early stages of biofilm formation

Unraveling the complex regulatory networks in biofilm formation in bacteria and relevance of biofilms in environmental remediation

Biofilms are assemblages of bacteria embedded within a matrix of extracellular polymeric substances (EPS) attached to a substratum. The process of biofilm formation is a complex phenomenon regulated by the intracellular and intercellular signaling systems. Various secondary messenger molecules such as cyclic dimeric guanosine 3',5'-monophosphate (c-di-GMP), cyclic adenosine 3',5'-monophosphate (cAMP), and cyclic dimeric adenosine 3',5'-monophosphate (c-di-AMP) are involved in complex signaling networks to regulate biofilm development in several bacteria. Moreover, the cell to cell communication system known as Quorum Sensing (QS) also regulates biofilm formation via diverse mechanisms in various bacterial species. Bacteria often switch to the biofilm lifestyle in the presence of toxic pollutants to improve their survivability. Bacteria within a biofilm possess several advantages with regard to the degradation of harmful pollutants, such as increased protection within the biofilm to resist the toxic pollutants, synthesis of extracellular polymeric substances (EPS) that helps in the sequestration of pollutants, elevated catabolic gene expression within the biofilm microenvironment, higher cell density possessing a large pool of genetic resources, adhesion ability to a wide range of substrata, and metabolic heterogeneity. Therefore, a comprehensive account of the various factors regulating biofilm development would provide valuable insights to modulate biofilm formation for improved bioremediation practices. This review summarizes the complex regulatory networks that influence biofilm development in bacteria, with a major focus on the applications of bacterial biofilms for environmental restoration.

Rutin, A Natural Inhibitor of IGPD Protein, Partially Inhibits Biofilm Formation in Staphylococcus xylosus ATCC700404 in vitro and in vivo

Staphylococcus xylosus (S. xylosus) has become an emerging opportunistic pathogen due to its strong biofilm formation ability. Simultaneously, the biofilm of bacteria plays an important role in antibiotic resistance and chronic infection. Here, we confirmed that rutin can effectively inhibit biofilm formation in S. xylosus, of which the inhibition mechanism involves its ability to interact with imidazole glycerol phosphate dehydratase (IGPD), a key enzyme in the process of biofilm formation. We designed experiments to target IGPD and inhibited its activities against S. xylosus. Our results indicated that the activity of IGPD and the amount of histidine decreased significantly under the condition of 0.8 mg/ml rutin. Moreover, the expression of IGPD mRNA (hisB) and IGPD protein was significantly down-regulated. Meanwhile, the results from molecular dynamic simulation and Bio-layer interferometry (BLI) technique showed that rutin could bind to IGPD strongly. Additionally, in vivo studies demonstrated that rutin treatment reduced inflammation and protect mice from acute mastitis caused by S. xylosus. In summary, our findings provide new insights into the treatment of biofilm mediated persistent infections and chronic bacterial infections. It could be helpful to design next generation antibiotics to against resistant bacteria.

Quartz tuning fork mass change sensing for FIB/SEM technology

In this paper we present a metrological method for determination of mass density of focused ion beam induced deposition (FIBID) materials using quartz tuning fork (QTF) mass change sensors. Dimension and density determination of FIBID deposited nanostructures is necessary to develop and reliable and repeatable microfabribrication technology of the highest versatility. The proposed metrological methodology allows to determine mass change with 5 pg resolution and accuracy below 5 % if density is considered. The described method is suitable for precise FIBID precursor parameters determination conducted during the deposition as actuation and signal read-out of the applied QTF can be performed electrically. High accuracy, resolution and stability are ensured due to excellent properties of quartz forming the sensor structure.

Options and Limitations in Clinical Investigation of Bacterial Biofilms

Bacteria can form single- and multispecies biofilms exhibiting diverse features based upon the microbial composition of their community and microenvironment. The study of bacterial biofilm development has received great interest in the past 20 years and is motivated by the elegant complexity characteristic of these multicellular communities and their role in infectious diseases. Biofilms can thrive on virtually any surface and can be beneficial or detrimental based upon the community's interplay and the surface. Advances in the understanding of structural and functional variations and the roles that biofilms play in disease and host-pathogen interactions have been addressed through comprehensive literature searches. In this review article, a synopsis of the methodological landscape of biofilm analysis is provided, including an evaluation of the current trends in methodological research. We deem this worthwhile because a keyword-oriented bibliographical search reveals that less than 5% of the biofilm literature is devoted to methodology. In this report, we (i) summarize current methodologies for biofilm characterization, monitoring, and quantification; (ii) discuss advances in the discovery of effective imaging and sensing tools and modalities; (iii) provide an overview of tailored animal models that assess features of biofilm infections; and (iv) make recommendations defining the most appropriate methodological tools for clinical settings.

Adhesion forces of biofilms developed in vitro from clinical strains of skin wounds

A biofilm is a very complex consortium formed by a mix of different microorganisms, which have become an important health problem, because its formation is a resistance mechanism used by bacteria against antibiotics or the immune system. In this work, we show differences between some physicochemical properties of biofilms in mono- and multi-species, formed by bacteria from clinical samples of infected chronic wounds. Of the most prevalent bacteria in wounds, two mono- and one multi-species biofilms were developed in vitro by Drip Flow Reactor: one biofilm was developed by S. aureus, other by P. aeruginosa, and a third one by the mix of both strains. With these biofilms, we determined microbial growth by plate counting, and their physicochemical characterization by Atomic Force Microscopy, Raman Micro-Spectroscopy and Scanning Electron Microscopy. We found that the viability of S. aureus was less than P. aeruginosa in multi-species biofilm. However, the adhesion force of S. aureus is much higher than that of P. aeruginosa, but it decreased while that of P. aeruginosa increased in the multi-species biofilm. In addition, we found free pyrimidines functional groups in the P. aeruginosa biofilm and its mix with S. aureus. Surprisingly, each bacterium alone formed single layer biofilms, while the mix bacteria formed a multilayer biofilm at the same observation time. Our results show the necessity to evaluate biofilms from clinically isolated strains and have a better understanding of the adhesion forces of bacteria in biofilm multispecies, which could be of prime importance in developing more effective treatments against biofilm formation.

Piezoelectric tuning fork biosensors for the quantitative measurement of biomolecular interactions

The quantitative measurement of biomolecular interactions is of great interest in molecular biology. Atomic force microscopy (AFM) has proved its capacity to act as a biosensor and determine the affinity between biomolecules of interest. Nevertheless, the detection scheme presents certain limitations when it comes to developing a compact biosensor. Recently, piezoelectric quartz tuning forks (QTFs) have been used as laser-free detection sensors for AFM. However, only a few studies along these lines have considered soft biological samples, and even fewer constitute quantified molecular recognition experiments. Here, we demonstrate the capacity of QTF probes to perform specific interaction measurements between biotin-streptavidin complexes in buffer solution. We propose in this paper a variant of dynamic force spectroscopy based on representing adhesion energies E (aJ) against pulling rates v (nm s(-1)). Our results are compared with conventional AFM measurements and show the great potential of these sensors in molecular interaction studies.

Nanoscale imaging of the growth and division of bacterial cells on planar substrates with the atomic force microscope

With the use of the atomic force microscope (AFM), the Nanomicrobiology field has advanced drastically. Due to the complexity of imaging living bacterial processes in their natural growing environments, improvements have come to a standstill. Here we show the in situ nanoscale imaging of the growth and division of single bacterial cells on planar substrates with the atomic force microscope. To achieve this, we minimized the lateral shear forces responsible for the detachment of weakly adsorbed bacteria on planar substrates with the use of the so called dynamic jumping mode with very soft cantilever probes. With this approach, gentle imaging conditions can be maintained for long periods of time, enabling the continuous imaging of the bacterial cell growth and division, even on planar substrates. Present results offer the possibility to observe living processes of untrapped bacteria weakly attached to planar substrates.

Micropattern of antibodies imaged by shear force microscopy: comparison between classical and jumping modes

Quartz tuning fork devices are increasingly being used as nanosensors in Scanning Probe Microscopy. They offer some benefits with respect to standard microfabricated cantilevers in certain experimental setups including the study of biomolecules under physiological conditions. In this work, we compare three different working modes for imaging micropatterned antibodies with quartz tuning fork sensors: apart from the classical amplitude and frequency modulation strategies, for first time the jumping mode is implemented using tuning forks. Our results show that the molecules suffer less degradation when working in the jumping mode, due to the reduction of the interaction forces.