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Biorecognition Elements in Biosensors
Published in Sibel A. Ozkan, Bengi Uslu, Mustafa Kemal Sezgintürk, Biosensors, 2023
Michael López Mujica, Alejandro Tamborelli, Virginia Vaschetti, Pablo Gallay, Fabrizio Perrachione, Daiana Reartes, Rocío Delpino, Marcela Rodríguez, María D. Rubianes, Pablo Dalmasso, Gustavo Rivas
Lectin-modified surfaces have been mainly used as sensor platforms for the determination of sugars and glycoproteins. In addition, bacterial toxins can also be detected through lectin complexation because they often contain sugar moieties like the lipopolysaccharides located on the outer membrane of Gram-negative bacteria, and lipoteichoic acid found in Gram-positive bacteria (28). Lectin-modified sensors have also been used for detecting cells by exploiting the selective binding of lectins to hydrocarbon chains located on the surface of cells (29). Among cells, the detection of cancer cells is particularly important due to the presence of glyco-proteins and glycolipids on their surface (27). Lectin-sensing bioplatforms are also important since lectins, in addition, play a prominent role in the immune system ranging from pathogen recognition and tuning of inflammation to cell adhesion or cellular signalling (30).
Infection and Inflammation
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Erik H. J. G. Aarntzen, Andor W. J. M. Glaudemans
Although inflammatory responses can be triggered by physical or chemical stimuli, with in general overlapping characteristics, this chapter focuses on the response on pathogenic stimuli such as bacteria, viruses, and parasites. Pathogenic microorganisms elicit an immunological response once they have crossed the epithelial barriers – for example, skin, mucosal lining of the gastro-intestinal tract, or the respiratory system. At these large surface areas, cells of the innate immune system, such as neutrophils and tissue resident macrophages (e.g. Kupffer cells, Langerhans cells, alveolar macrophages) are actively surveilling [1-3]. Although these cells lack the specificity of the adaptive immune system, they express pattern-recognition receptors that recognize classes of molecules present on pathogens. For example, toll-like receptors (TLRs) recognize molecular patterns that are not found in normal vertebrates – for example, lipopolysaccharide (LPS), a component of bacterial cell wall that is recognized by TLR-4. Mannose receptors are expressed on macrophages to recognize sugar molecules present on most bacteria and some viruses. Scavenger receptors bind negatively charged cell-wall components from gram-positive bacteria, such as lipoteichoic acid.
Immune Reactions in the Delivery of RNA Interference-Based Therapeutics: Mechanisms and Opportunities
Published in Raj Bawa, János Szebeni, Thomas J. Webster, Gerald F. Audette, Immune Aspects of Biopharmaceuticals and Nanomedicines, 2019
Kaushik Thanki, Emily Falkenberg, Monique Gangloff, Camilla Foged
The most widely studied and promiscuous receptors for lipid recognition are probably TLR2 and TLR4. There is increasing evidence that PRRs have both canonical and atypical ligands. TLR2 senses cell-wall components, lipoteichoic acid and lipoproteins from gram-positive bacteria; lipoarabinomannan from mycobacteria; and zymosan from yeast [85]. Ligand recognition requires either homodimerization or heterodimerization with TLR1 or TLR6 via direct binding to their 20 LRR-long ectodomains [86, 87]. While lipopeptide binding has been characterized by crystallography, atypical ligand binding remains a mystery. It has been shown that triacylated lipopeptides are recognized by the TLR2-TLR1 heterodimer that accommodates the lipid chains in hydrophobic cavities within LRR9–12. TLR1 buries a single chain linked by an amide linkage almost perpendicular to the two ester-bound chains concealed in TLR2 [86]. In contrast, diacylated lipopeptides recruit TLR2-TLR6 heterodimers. The lack of hydrophobic cavity in TLR6 complements perfectly the lack of amide-bound lipid, while increased protein-protein interactions compensate the absence of ligand tether, compared to TLR1 heterodimers. TLR2, as well as NLRP3, have been implicated in cationic lipid signalling [88], but their mechanism of action is not fully resolved. Docking studies performed on a family of di-C18 cationic lipids suggest that they bind in a manner reminiscent of lipopeptides preferentially to TLR2-TLR1 heterodimers, despite only having two aliphatic chains [89].
Evaluating the fabric performance and antibacterial properties of 3-D piezoelectric spacer fabric
Published in The Journal of The Textile Institute, 2018
Derman Vatansever Bayramol, Navneet Soin, Amrita Dubey, Ravi Kant Upadhyay, Richa Priyadarshini, Susanta Sinha Roy, Tahir H. Shah, Subhash C. Anand
The results revealed that silver coated 3-D piezoelectric fabrics exhibit antibacterial activity against not only Gram-negative bacteria E. coli but it is also capable of killing antibiotic methicillin-resistant bacteria S. aureus (Stapleton & Taylor, 2002). The 3-D silver-coated fabric is found to be less potent as antibacterial against Gram-positive bacteria S. aureus, as compared to the Gram-negative bacteria E. coli; this observation is in well agreement with several previously published reports. Previously, several studies have reported better antibacterial activity of the silver nanoparticles against Gram-negative bacteria, as compared to the Gram-positive bacteria S. Aureus (Kim, Lee, Ryu, Choi, & Lee, 2011; Cavassin et al., 2015; Taglietti et al., 2012; Amato et al., 2011). The reason behind better bacteriocidal activity of the Ag against S. aureus compare to the E. coli is believed to be because of the complex cell membrane structure of the S. aureus compare to E. coli. The S. aureus contains thick lipoteichoic acid containing peptidoglycan layer and cell membrane as compared to the E. coli (Kim et al., 2011). The thickness of the peptidoglycan layer for S. aureus and E. coli is estimated to be in the range of 20–80 nm and 7–8 nm, respectively. The thicker peptidoglycan layer of the S. aureus provides it better protection compared to the E. coli against the attack of the reactive oxygen species (ROS) generated by the silver. Thus, the 3-D fabric samples are highly effective in stopping the growth and propagation of both the Gram-positive and Gram-negative bacteria and as such could be used for fabrication of smart functional textiles with antibacterial properties.
Arene platinum group metal complexes containing imino-quinolyl ligands: synthesis and antibacterial studies
Published in Journal of Coordination Chemistry, 2020
Agreeda Lapasam, Sanjay Adhikari, Venkanna Banothu, Uma Addepally, Mohan Rao Kollipara
The antibacterial activity of the starting metal precursors of [(p-cymene)RuCl2]2, [(benzene)RuCl2]2, [Cp*RhCl2]2 and [Cp*IrCl2]2 were found to be inactive as previously reported [31]. All the complexes displayed effective antibacterial activity against all the studied bacterial strains, but p-cymene ruthenium chelates have high antibacterial activity. The slightly better activity for some metal chelates compared to the free ligands can be elucidated on the basis of chelation theory [32]. In vitro assay results revealed that ligands and complexes were more active against the Gram-negative bacteria than against the Gram-positive bacterium. The variance in the effectiveness of the complexes against the tested organisms is based on the difference in the cell wall structure of the Gram-negative and Gram-positive bacteria, ribosome of the microbial cells or impermeability of the cells of microbes [33]. A Gram-negative bacterium has a thin peptidoglycan layer and an outer membrane that contains proteins, lipopolysaccharide, and phospholipids, while a Gram-positive bacterium has a thick peptidoglycan layer that contains lipoteichoic acid. Hence, the cell wall of a Gram-negative bacterium is more polar, and the permeation of complexes into the microorganism is enabled by this polarity. Therefore, the effectiveness of the investigated compounds against K. pneumoniae is greater than against S. aureus. Furthermore, the results show that p-cymene ruthenium complex 1, complex 5, complex 9 and Cp*rhodium complex 7 showed good activity whereas benzene ruthenium complex 2 and 6 showed the least activity compared to other complexes. The comparison of metal ion with free ligands has been made and the results are presented in Figure 4.
Fluorescent optotracers for bacterial and biofilm detection and diagnostics
Published in Science and Technology of Advanced Materials, 2023
Agneta Richter-Dahlfors, Elina Kärkkäinen, Ferdinand X. Choong
The oligothiophene backbone of optotracers can be varied such that the central thiophene unit is replaced by heterocyclic motifs. By analyzing the signal quality of such optotracers interacting with S. aureus, it was shown that the presence of a central quinoxaline motif resulted in the most distinct signal of bound optotracers compared to the unbound state [90]. These findings were also a strong indication of the benefits in spectral separation and sensitivity brought about by heterocyclic motifs conferring a donor-acceptor-donor (D-A-D) type electronic structure in the optotracers’ conjugated backbone [85,91,100]. In order to identify the binding target of the optotracer on S. aureus cells, a genetic approach was taken, in which an unbiased screen of approximately 2000 isogenic strains of a S. aureus transposon library were used, in which each strain harbored a well-defined mutation in a nonessential gene [101]. Finding that the optotracer bound all strains within the transposon library implied that the binding target was likely the product of essential gene(s) [90]. Comparative analysis of fluorescence signals between strains revealed, however, instances of attenuated fluorescence, of which >60% were related to genes involved in the formation of the cell envelope. Optotracing of purified preparations of cell envelope components showed positive binding to peptidoglycan and lipoteichoic acid, whereas LPS from gram-negative bacteria remained unstained as expected. This was strong evidence pointing to the cell wall as a target for optotracers. Necessitated by the large pool of samples and the considerable amount of data within absorption and emission patterns, an efficient workflow using algorithm-based analytics had to be developed to enable automated data analysis (Figure 3). In this workflow, a bacterial culture was prepared by re-inoculating an overnight culture into fresh growth media supplemented with the optotracer. As the culture was incubated, culture density was monitored by traditional absorbance recordings as well as recording of the intensity of the fluorescence signals from the optotracer bound to S. aureus cells. Extracted data was then processed by a custom-made script which calculated the generation time and correlated fluorescence intensity with the measured absorbance. Given that the correlation was linear, the value of the slope of the correlation curve could be used to guide the evaluation of optotracer binding throughout different growth phases without influencing the growth conditions [91]. This generated a possibility to perform continuous monitoring, which represents an important step towards the translation of optotracing methodologies into bedside diagnostic tools, since the momentous state of the sample can be evaluated conveniently and without the necessity of an external reference.