Biosensors for the Detection of Interaction between Legionella pneumophila Collagen-Like Protein and Glycosaminoglycans

The Legionella collagen-like protein employs a distinct binding mechanism for the recognition of host glycosaminoglycans

Bacterial adhesion is a fundamental process which enables colonisation of niche environments and is key for infection. However, in Legionella pneumophila, the causative agent of Legionnaires' disease, these processes are not well understood. The Legionella collagen-like protein (Lcl) is an extracellular peripheral membrane protein that recognises sulphated glycosaminoglycans on the surface of eukaryotic cells, but also stimulates bacterial aggregation in response to divalent cations. Here we report the crystal structure of the Lcl C-terminal domain (Lcl-CTD) and present a model for intact Lcl. Our data reveal that Lcl-CTD forms an unusual trimer arrangement with a positively charged external surface and negatively charged solvent exposed internal cavity. Through molecular dynamics simulations, we show how the glycosaminoglycan chondroitin-4-sulphate associates with the Lcl-CTD surface via distinct binding modes. Our findings show that Lcl homologs are present across both the Pseudomonadota and Fibrobacterota-Chlorobiota-Bacteroidota phyla and suggest that Lcl may represent a versatile carbohydrate-binding mechanism.

The Legionella collagen-like protein employs a unique binding mechanism for the recognition of host glycosaminoglycans

Bacterial adhesion is a fundamental process which enables colonisation of niche environments and is key for infection. However, in Legionella pneumophila, the causative agent of Legionnaires' disease, these processes are not well understood. The Legionella collagen-like protein (Lcl) is an extracellular peripheral membrane protein that recognises sulphated glycosaminoglycans (GAGs) on the surface of eukaryotic cells, but also stimulates bacterial aggregation in response to divalent cations. Here we report the crystal structure of the Lcl C-terminal domain (Lcl-CTD) and present a model for intact Lcl. Our data reveal that Lcl-CTD forms an unusual dynamic trimer arrangement with a positively charged external surface and a negatively charged solvent exposed internal cavity. Through Molecular Dynamics (MD) simulations, we show how the GAG chondroitin-4-sulphate associates with the Lcl-CTD surface via unique binding modes. Our findings show that Lcl homologs are present across both the Pseudomonadota and Fibrobacterota-Chlorobiota-Bacteroidota phyla and suggest that Lcl may represent a versatile carbohydrate binding mechanism.

An electrochemical biosensor for the detection of aflatoxin B1 based on the specific aptamer and HCR biological magnification

Aflatoxin B1 (AFB1) is a highly toxic mycotoxin, which causes severe acute or cumulative poisoning. Therefore, it is important to develop sensitive and selective detection methods for AFB1 for the safety of food and medicinal herbs. Herein, we have developed a "signal-on" electrochemical aptasensor based on the high specificity of the aptamer and hybridization chain reaction (HCR) biological amplification for AFB1 detection. In this work, thiol-modified complementary DNA (cDNA) immobilized on the surface of a gold electrode (GE) served as an initiator DNA. When AFB1 was present, it competed with the cDNA for binding to the aptamers, which resulted in the detaching of aptamers from the cDNA-aptamer duplexes. Then, the single-stranded cDNA acted as an initiator to trigger the HCR signal amplification. Therefore, long double-stranded DNA (dsDNA) products were produced, which could load large amounts of methylene blue (MB) molecules to generate a distinct electrochemical signal. Under the optimized conditions, the proposed electrochemical aptasensor achieved the ultrasensitive detection of AFB1 with a linear detection range of 0.01-100 pg mL^-1, and a limit of detection (LOD) down to 2.84 fg mL^-1. Furthermore, the electrochemical aptasensor was successfully applied for detecting AFB1 in corn and two kinds of traditional Chinese medicine samples, indicating the potential value for AFB1 detection in practical samples.

Host-Pathogen Adhesion as the Basis of Innovative Diagnostics for Emerging Pathogens

Infectious diseases are an existential health threat, potentiated by emerging and re-emerging viruses and increasing bacterial antibiotic resistance. Targeted treatment of infectious diseases requires precision diagnostics, especially in cases where broad-range therapeutics such as antibiotics fail. There is thus an increasing need for new approaches to develop sensitive and specific in vitro diagnostic (IVD) tests. Basic science and translational research are needed to identify key microbial molecules as diagnostic targets, to identify relevant host counterparts, and to use this knowledge in developing or improving IVD. In this regard, an overlooked feature is the capacity of pathogens to adhere specifically to host cells and tissues. The molecular entities relevant for pathogen–surface interaction are the so-called adhesins. Adhesins vary from protein compounds to (poly-)saccharides or lipid structures that interact with eukaryotic host cell matrix molecules and receptors. Such interactions co-define the specificity and sensitivity of a diagnostic test. Currently, adhesin-receptor binding is typically used in the pre-analytical phase of IVD tests, focusing on pathogen enrichment. Further exploration of adhesin–ligand interaction, supported by present high-throughput “omics” technologies, might stimulate a new generation of broadly applicable pathogen detection and characterization tools. This review describes recent results of novel structure-defining technologies allowing for detailed molecular analysis of adhesins, their receptors and complexes. Since the host ligands evolve slowly, the corresponding adhesin interaction is under selective pressure to maintain a constant receptor binding domain. IVD should exploit such conserved binding sites and, in particular, use the human ligand to enrich the pathogen. We provide an inventory of methods based on adhesion factors and pathogen attachment mechanisms, which can also be of relevance to currently emerging pathogens, including SARS-CoV-2, the causative agent of COVID-19.

Label-Free Electrochemical Sensor for Rapid Bacterial Pathogen Detection Using Vancomycin-Modified Highly Branched Polymers

Rapid point of care tests for bacterial infection diagnosis are of great importance to reduce the misuse of antibiotics and burden of antimicrobial resistance. Here, we have successfully combined a new class of non-biological binder molecules with electrochemical impedance spectroscopy (EIS)-based sensor detection for direct, label-free detection of Gram-positive bacteria making use of the specific coil-to-globule conformation change of the vancomycin-modified highly branched polymers immobilized on the surface of gold screen-printed electrodes upon binding to Gram-positive bacteria. Staphylococcus carnosus was detected after just 20 min incubation of the sample solution with the polymer-functionalized electrodes. The polymer conformation change was quantified with two simple 1 min EIS tests before and after incubation with the sample. Tests revealed a concentration dependent signal change within an OD600 range of Staphylococcus carnosus from 0.002 to 0.1 and a clear discrimination between Gram-positive Staphylococcus carnosus and Gram-negative Escherichia coli bacteria. This exhibits a clear advancement in terms of simplified test complexity compared to existing bacteria detection tests. In addition, the polymer-functionalized electrodes showed good storage and operational stability.

Legionella pneumophila Attachment to Biofilms of an Acidovorax Isolate from a Drinking Water-Consortium Requires the Lcl-Adhesin Protein

Human infection by Legionella pneumophila (Lpn) only occurs via contaminated water from man-made sources, and eradication of these bacteria from man-made water systems is complicated by biofilm colonization. Using a continuously fed biofilm reactor model, we grew a biofilm consortium from potable water that was able to prolong recovery of Lpn CFU from biofilms. This effect was recreated using a subset of those species in a simplified consortium composed of eight bacterial isolates from the first biofilm reactor. In the reactor with the eight-species consortium, Lpn biofilm CFU was relatively stable over a 12-day trial. An isolate of Acidovorax from the consortium was, as a single species biofilm, able to promote Lpn surface attachment. Other isolates from the Pelomonas genus grew as equally robust biofilms alone, but did not promote surface attachment of Lpn. This attachment was disrupted by cationic polysaccharides and loss of the Lpn Lcl collagen-like adhesin protein. This work demonstrates that, while Lpn was fairly incompetent at attachment to surfaces to form a biofilm alone, pre-existing biofilms allowed attachment of Lpn as secondary colonizers. In addition, we demonstrate that initial attachment of Lpn to Acidovorax biofilms is likely via the Lcl-adhesin protein.

Low molecular weight fucoidan alleviates diabetic nephropathy by binding fibronectin and inhibiting ECM-receptor interaction in human renal mesangial cells

Diabetic nephropathy (DN) is the most common cause of end-stage renal disease (ESRD). Currently, approximately 20-40% of individuals with diabetes are diagnosed with DN. Mesangial cells (MCs) are critical for maintaining and regulating glomerular filtration, and the abnormal proliferation of MCs causes the accumulation of mesangial extracellular matrix (ECM), further promoting glomerular dysfunction and renal diseases. Low molecular weight fucoidan (LMWF) extracted from Saccharina japonica could alleviate DN, but the mechanism was not analysed. Based on the ability of LMWF to ameliorate the human renal mesangial cell (HRMC) injury caused by advanced glycation end products (AGEs), we identified fibronectin (FN) as the most obviously impacted protein in the ECM-receptor interaction by proteomic analysis. The co-localization of LMWF and FN indicated direct interaction between them, and surface plasmon resonance (SPR) analysis confirmed the specific binding with a K_D of 453.7 μmol L^-1. Positively charged protamine sulfate (PS) promoted the combination of LMWF and HRMCs and further enhanced the effect of LMWF on HRMC injury. Our results indicated that LMWF alleviates the HRMC injury caused by AGEs via binding FN and inhibiting the ECM-receptor interaction pathway. These results provide a foundation for the in-depth analysis of the mechanism of polysaccharide functions.

A Review of the Internet of Floods: Near Real-Time Detection of a Flood Event and Its Impact

Worldwide, flood events frequently have a dramatic impact on urban societies. Time is key during a flood event in order to evacuate vulnerable people at risk, minimize the socio-economic, ecologic and cultural impact of the event and restore a society from this hazard as quickly as possible. Therefore, detecting a flood in near real-time and assessing the risks relating to these flood events on the fly is of great importance. Therefore, there is a need to search for the optimal way to collect data in order to detect floods in real time. Internet of Things (IoT) is the ideal method to bring together data of sensing equipment or identifying tools with networking and processing capabilities, allow them to communicate with one another and with other devices and services over the Internet to accomplish the detection of floods in near real-time. The main objective of this paper is to report on the current state of research on the IoT in the domain of flood detection. Current trends in IoT are identified, and academic literature is examined. The integration of IoT would greatly enhance disaster management and, therefore, will be of greater importance into the future.

DNA-based bioassay of legionella pneumonia pathogen using gold nanostructure: A new platform for diagnosis of legionellosis

The specific diagnosis of hard-growing bacteria is one of the most important concerns of medical bacteriology. Legionella pneumophila is one of the most important bacteria in hard growth. In spite remarkable trends in bacteriology, now day, culture is the gold standard for detection of L. pneumophila. This work is an attempt to quantification of L. pneumophila bacteria using a bioassay. The fabrication of a new electrochemical DNA-based bioassay using gold nano architecture combined with as a transducer substrate combined with toluidine blue (TB) as a redox marker was performed successful. Also, the mixture of beta‑cyclodextrin and dopamine as Poly (dopamine‑β‑Cyclodextrin) was used to proper a biointerface for stabilization of gold nanoparticles optimum immobilize of pDNA sequence (5-SH-TCGA TAC TCT CCC CGC CCC TT T TGTATCGACG-3). So, a specific thiolated pDNA was immobilized on the transducer substrate and DNA hybridization was followed by C-DNA sequence (5-ACA AAA GGG GCG GGG AGA GTA-3) using square wave voltammetry and differential pulse voltammetry. At the optimum conditions, linear range was 1 μM to 1 ZM and low limit of quantification (LLOQ) was 1 Zepto-molar. L. pneumophila were sensitively distinguished by the planned DNA sensor. Finally, the engineered DNA based bioassay could be used for identifying the L. pneumophila samples from patients or environments.