Development of a high-throughput screen and its use in the discovery of Streptococcus pneumoniae immunoglobulin A1 protease inhibitors

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Bacterial keratitis: identifying the areas of clinical uncertainty

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

LSPR-based colorimetric biosensing for food quality and safety

Ensuring consistently high quality and safety is paramount to food producers and consumers alike. Wet chemistry and microbiological methods provide accurate results, but those methods are not conducive to rapid, onsite testing needs. Hence, many efforts have focused on rapid testing for food quality and safety, including the development of various biosensors. Herein, we focus on a group of biosensors, which provide visually recognizable colorimetric signals within minutes and can be used onsite. Although there are different ways to achieve visual color-change signals, we restrict our focus on sensors that exploit the localized surface plasmon resonance (LSPR) phenomenon of metal nanoparticles, primarily gold and silver nanoparticles. The typical approach in the design of LSPR biosensors is to conjugate biorecognition ligands on the surface of metal nanoparticles and allow the ligands to specifically recognize and bind the target analyte. This ligand-target binding reaction leads to a change in color of the test sample and a concomitant shift in the ultraviolet-visual absorption peak. Various designs applying this and other signal generation schemes are reviewed with an emphasis on those applied for evaluating factors that compromise the quality and safety of food and agricultural products. The LSPR-based colorimetric biosensing platform is a promising technology for enhancing food quality and safety. Aided by the advances in nanotechnology, this sensing technique lends itself easily for further development on field-deployable platforms such as smartphones for onsite and end-user applications.

Immunoglobulin A Glycosylation and Its Role in Disease

Human IgA is comprised of two subclasses, IgA1 and IgA2. Monomeric IgA (mIgA), polymeric IgA (pIgA), and secretory IgA (SIgA) are the main molecular forms of IgA. The production of IgA rivals all other immunoglobulin isotypes. The large quantities of IgA reflect the fundamental roles it plays in immune defense, protecting vulnerable mucosal surfaces against invading pathogens. SIgA dominates mucosal surfaces, whereas IgA in circulation is predominately monomeric. All forms of IgA are glycosylated, and the glycans significantly influence its various roles, including antigen binding and the antibody effector functions, mediated by the Fab and Fc portions, respectively. In contrast to its protective role, the aberrant glycosylation of IgA1 has been implicated in the pathogenesis of autoimmune diseases, such as IgA nephropathy (IgAN) and IgA vasculitis with nephritis (IgAVN). Furthermore, detailed characterization of IgA glycosylation, including its diverse range of heterogeneity, is of emerging interest. We provide an overview of the glycosylation observed for each subclass and molecular form of IgA as well as the range of heterogeneity for each site of glycosylation. In many ways, the role of IgA glycosylation is in its early stages of being elucidated. This chapter provides an overview of the current knowledge and research directions.

Small-Molecule Inhibitors of Haemophilus influenzae IgA1 Protease

Newly identified, nontypable Haemophilus influenzae (H. influenza) strains represent a serious threat to global health. Due to the increasing prevalence of antibiotic resistance, virulence factors have emerged as potential therapeutic targets that would be less likely to promote resistance. IgA1 proteases are secreted virulence factors of many Gram-negative human pathogens. These enzymes play important roles in tissue invasion as well as evasion of the immune response, yet there has been limited work on pharmacological inhibitors. Here, we report the discovery of the first small molecule, nonpeptidic inhibitors of H. influenzae IgA1 proteases. We screened over 47 000 compounds in a biochemical assay using recombinant protease and identified a hit compound with micromolar potency. Preliminary structure-activity relationships produced additional inhibitors, two of which showed improved inhibition and selectivity for IgA protease over other serine proteases. We further showed dose-dependent inhibition against four different IgA1 protease variants collected from clinical isolates. These data support further development of IgA protease inhibitors as potential therapeutics for antibiotic-resistant H. influenza strains. The newly discovered inhibitors also represent valuable probes for exploring the roles of these proteases in bacterial colonization, invasion, and infection of mucosal tissues.

The influence of etiological factors on immunoreactivity in patients with community-acquired pneumonia

 The aim of this study was to uncover the characteristics of immunoreactivity in patients with community-acquired pneumonia, depending on the pathogen. The inflammatory process caused by various pathogens, has its own characteristics and affects the course of the disease. The study of the mechanisms of these complex interactions can improve the understanding of the processes occurring in community-acquired pneumonia, and, therefore, develop individual approaches to the therapy depending on the etiological factor.

Gold nanoparticle-based colorimetric biosensors

Gold nanoparticles (AuNPs) provide excellent platforms for the development of colorimetric biosensors as they can be easily functionalised, displaying different colours depending on their size, shape and state of aggregation. In the last decade, a variety of biosensors have been developed to exploit the extent of colour changes as nano-particles (NPs) either aggregate or disperse, in the presence of analytes. Of critical importance to the design of these methods is that the behaviour of the systems has to be reproducible and predictable. Much has been accomplished in understanding the interactions between a variety of substrates and AuNPs, and how these interactions can be harnessed as colorimetric reporters in biosensors. However, despite these developments, only a few biosensors have been used in practice for the detection of analytes in biological samples. The transition from proof of concept to market biosensors requires extensive long-term reliability and shelf life testing, and modification of protocols and design features to make them safe and easy to use by the population at large. Developments in the next decade will see the adoption of user friendly biosensors for point-of-care and medical diagnosis as innovations are brought to improve the analytical performances and usability of the current designs. This review discusses the mechanisms, strategies, recent advances and perspectives for the use of AuNPs as colorimetric biosensors.

Immunoglobulins and their receptors, and subversion of their protective roles by bacterial pathogens

Immunoglobulins (Igs) play critical roles in immune defence against infectious disease. They elicit potent elimination processes such as triggering complement activation and engaging specific Fc receptors present on immune cells, resulting in phagocytosis and other killing mechanisms. Many important pathogens have evolved mechanisms to subvert or evade Ig-mediated defence. One such mechanism used by several pathogenic bacteria features proteins that bind the Ig Fc region and compromise engagement of host effector molecules. Examples include different IgA-binding proteins produced by Staphylococcus aureus, Streptococcus pyogenes, and group B streptococci, all of which interact with the same interdomain region on IgA Fc. Since this region also forms the interaction site for the major human IgA-specific Fc receptor CD89, the bacteria are able to evade CD89-mediated clearance mechanisms. Similar disruption of Ig effector function by pathogen Ig-binding proteins is evident in other species. Remarkably, all the Ig-binding proteins studied in detail to date are seen to target the CH2-CH3 domain interface in the Ig Fc region, suggesting a common mode of immune evasion. A second Ig subversion mechanism that has evolved independently in numerous pathogens involves proteases that cleave Ig molecules within their hinge regions, uncoupling the antigen recognition capability of the Fab region from clearance mechanisms elicited by the Fc region. The emerging understanding of the structural basis for the recognition of Igs as substrates for these proteases and as interaction partners for Ig-binding proteins may open up new avenues for treatment or vaccination.

Colorimetric biosensing of pathogens using gold nanoparticles

Rapid detection of pathogens is crucial to minimize adverse health impacts of nosocomial, foodborne, and waterborne diseases. Gold nanoparticles are extremely successful at detecting pathogens due to their ability to provide a simple and rapid color change when their environment is altered. Here, we review general strategies of implementing gold nanoparticles in colorimetric biosensors. First, we highlight how gold nanoparticles have improved conventional genomic analysis methods by lowering detection limits while reducing assay times. Then, we focus on emerging point-of-care technologies that aim at pathogen detection using simpler assays. These advances will facilitate the implementation of gold nanoparticle-based biosensors in diverse environments throughout the world and help prevent the spread of infectious diseases.