Modulation of Quorum Sensing in a Gram-Positive Pathogen by Linear Molecularly Imprinted Polymers with Anti-infective Properties

Peptide maturation molecules act as molecular gatekeepers to coordinate cell-cell communication in Streptococcus pneumoniae

The human pathogen Streptococcus pneumoniae (Spn) encodes several cell-cell communication systems, notably multiple members of the Rgg/SHP and the Tpr/Phr families. Until now, members of these diverse communication systems were thought to work independently. Our study reveals that the ABC transporter PptAB and the transmembrane enzyme Eep act as a molecular link between Rgg/SHP and TprA/PhrA systems. We demonstrate that PptAB/Eep activates the Rgg/SHP systems and represses the TprA/PhrA system. Specifically, they regulate the respective precursor peptides (SHP and PhrA) before these leave the cell. This dual mode of action leads to temporal coordination of these systems, producing an overlap between their respective regulons during host cell infection. Thus, we have identified a single molecular mechanism that targets diverse cell-cell communication systems in Spn. Moreover, these molecular components are encoded by many gram-positive bacteria, suggesting that this mechanism may be broadly conserved.

Biological puzzles solved by using Streptococcus pneumoniae: a historical review of the pneumococcal studies that have impacted medicine and shaped molecular bacteriology

The major human pathogen Streptococcus pneumoniae has been the subject of intensive clinical and basic scientific study for over 140 years. In multiple instances, these efforts have resulted in major breakthroughs in our understanding of basic biological principles as well as fundamental tenets of bacterial pathogenesis, immunology, vaccinology, and genetics. Discoveries made with S. pneumoniae have led to multiple major public health victories that have saved the lives of millions. Studies on S. pneumoniae continue today, where this bacterium is being used to dissect the impact of the host on disease processes, as a powerful cell biology model, and to better understand the consequence of human actions on commensal bacteria at the population level. Herein we review the major findings, i.e., puzzle pieces, made with S. pneumoniae and how, over the years, they have come together to shape our understanding of this bacterium's biology and the practice of medicine and modern molecular biology.

Environmental and genetic regulation of Streptococcus pneumoniae galactose catabolic pathways

Efficient utilization of nutrients is crucial for microbial survival and virulence. The same nutrient may be utilized by multiple catabolic pathways, indicating that the physical and chemical environments for induction as well as their functional roles may differ. Here, we study the tagatose and Leloir pathways for galactose catabolism of the human pathogen Streptococcus pneumoniae. We show that galactose utilization potentiates pneumococcal virulence, the induction of galactose catabolic pathways is influenced differentially by the concentration of galactose and temperature, and sialic acid downregulates galactose catabolism. Furthermore, the genetic regulation and in vivo induction of each pathway differ, and both galactose catabolic pathways can be turned off with a galactose analogue in a substrate-specific manner, indicating that galactose catabolic pathways can be potential drug targets.

Tailor-made molecular imprints for biological event intervention

Molecular imprints, which are crosslinked architectures containing specific molecular recognition cavities for targeting compounds, have recently transitioned from in vitro diagnosis to in vivo treatment. In current application scenarios, it has become an important topic to create new biomolecular recognition pathways through molecular imprinting, thereby inhibiting the pathogenesis and regulating the development of diseases. This review starts with a pathological analysis, mainly focusing on the corresponding artificial enzymes, enzyme inhibitors and antibody mimics with enhanced functions that are created by molecular imprinting strategies. Recent advances are highlighted in the use of molecular imprints as tailor-made nanomedicines for the prevention of three major diseases: metabolic syndrome, cancer, and bacterial/viral infections.

The Amount of Cross-Linker Influences Affinity and Selectivity of NanoMIPs Prepared by Solid-Phase Polymerization Synthesis

The cross-linker methylene-bis-acrylamide is usually present in nanoMIPs obtained by solid-phase polymerization synthesis at 2 mol% concentration, with very few exceptions. Here, we studied the influence of variable amounts of methylene-bis-acrylamide in the range between 0 (no cross-linker) and 50 mol% concentration on the binding properties of rabbit IgG nanoMIPs. The binding parameters were determined by equilibrium binding experiments and the results show that the degree of cross-linking defines three distinct types of nanoMIPs: (i) those with a low degree of cross-linking, including nanoMIPs without cross-linker (0-05 mol%), showing a low binding affinity, high density of binding sites, and low selectivity; (ii) nanoMIPs with a medium degree of cross-linking (1-18 mol%), showing higher binding affinity, low density of binding sites, and high selectivity; (iii) nanoMIPs with a high degree of cross-linking (32-50 mol%), characterized by non-specific nanopolymer-ligand interactions, with low binding affinity, high density of binding sites, and no selectivity. In conclusion, the results are particularly relevant in the synthesis of high-affinity, high-selectivity nanoMIPs as they demonstrate that a significant gain in affinity and selectivity could be achieved with pre-polymerization mixtures containing quantities of cross-linker up to 10-20 mol%, well higher than those normally used in this technique.

Streptococcal peptides and their roles in host-microbe interactions

The genus Streptococcus encompasses many bacterial species that are associated with hosts, ranging from asymptomatic colonizers and commensals to pathogens with a significant global health burden. Streptococci produce numerous factors that enable them to occupy their host-associated niches, many of which alter their host environment to the benefit of the bacteria. The ability to manipulate host immune systems to either evade detection and clearance or induce a hyperinflammatory state influences whether bacteria are able to survive and persist in a given environment, while also influencing the propensity of the bacteria to cause disease. Several bacterial factors that contribute to this inter-species interaction have been identified. Recently, small peptides have become increasingly appreciated as factors that contribute to Streptococcal relationships with their hosts. Peptides are utilized by streptococci to modulate their host environment in several ways, including by directly interacting with host factors to disrupt immune system function and signaling to other bacteria to control the expression of genes that contribute to immune modulation. In this review, we discuss the many contributions of Streptococcal peptides in terms of their ability to contribute to pathogenesis and disruption of host immunity. This discussion will highlight the importance of continuing to elucidate the functions of these Streptococcal peptides and pursuing the identification of new peptides that contribute to modulation of host environments. Developing a greater understanding of how bacteria interact with their hosts has the potential to enable the development of techniques to inhibit these peptides as therapeutic approaches against Streptococcal infections.

Surface-Initiated Synthesis of Cell-Specific Glycopolymers Using Live Mammalian Cells as Templates

Molecular recognition is an important process in life activities where specificity is the key. However, the method to gain specificity are often complex and time-consuming. Herein, a novel, versatile, and effective way is developed to obtain cell-specific glycosurfaces by surface-initiated Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) in an open to air fashion. Mammalian cells are used for the first time as live templates to realize cell-sugar monomer-aptation-polymerization which can produce cell-specific glycosurfaces. Both epithelial cell adhesion molecule (EpCAM) positive cells L929 and EpCAM negative cells Hela as models are used to acquire two cell-specific glycosurfaces, which can distinguish template-cells from others. The strategy is effective and convenient without the need of fixative pretreatment of cells. It is found that the specific capture does not rely on EpCAM antibodies, and the specificity is related to the composition and chain sequence of the glycopolymer brushes rather than surface morphology. In addition, these glycosurfaces keep the ability to identify the target cells after ten regenerative treatments, which provides another advantage for practical applications.

Structure‐function analysis for development of peptide inhibitors for a Gram positive quorum sensing system

The Streptococcus pneumoniae Rgg144/SHP144 regulator‐peptide quorum sensing (QS) system is critical for nutrient utilization, oxidative stress response, and virulence. Here, we characterized this system by assessing the importance of each residue within the active short hydrophobic peptide (SHP) by alanine‐scanning mutagenesis and testing the resulting peptides for receptor binding and activation of the receptor. Interestingly, several of the mutations had little effect on binding to Rgg144 but reduced transcriptional activation appreciably. In particular, a proline substitution (P21A) reduced transcriptional activation by 29‐fold but bound with a 3‐fold higher affinity than the wild‐type SHP. Consistent with the function of Rgg144, the mutant peptide led to decreased utilization of mannose and increased susceptibility to superoxide generator paraquat. Pangenome comparison showed full conservation of P21 across SHP144 allelic variants. Crystallization of Rgg144 in the absence of peptide revealed a comparable structure to the DNA bound and free forms of its homologs suggesting similar mechanisms of activation. Together, these analyses identify key interactions in a critical pneumococcal QS system. Further manipulation of the SHP has the potential to facilitate the development of inhibitors that are functional across strains. The approach described here is likely to be effective across QS systems in multiple species.

Gene Expression Regulation in Airway Pathogens: Importance for Otitis Media

Otitis media (OM) is an inflammatory disorder in the middle ear. It is mainly caused by viruses or bacteria associated with the airways. Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the three main pathogens in infection-related OM, especially in younger children. In this review, we will focus upon the multifaceted gene regulation mechanisms that are well-orchestrated in S. pneumoniae, H. influenzae, and M. catarrhalis during the course of infection in the middle ear either in experimental OM or in clinical settings. The sophisticated findings from the past 10 years on how the othopathogens govern their virulence phenotypes for survival and host adaptation via phase variation- and quorum sensing-dependent gene regulation, will be systematically discussed. Comprehensive understanding of gene expression regulation mechanisms employed by pathogens during the onset of OM may provide new insights for the design of a new generation of antimicrobial agents in the fight against bacterial pathogens while combating the serious emergence of antimicrobial resistance.

Fighting Antibiotic-Resistant Bacteria : Promising Strategies Orchestrated by Molecularly Imprinted Polymers

Infections caused by antibiotic-resistant bacteria are difficult and sometimes impossible to treat, making them one of the major public health problems of our time. We highlight how one unique material , molecularly imprinted polymers (MIPs), can orchestrate several strategies to fight this major societal issue. MIPs are tailor-made biomimetic supramolecular receptors that recognize and bind target molecules with a high affinity and selectivity, comparable to those of antibodies. While research on MIPs for combatting cancer has been constantly flourishing, comprehensive work on their involvement in combatting resistant superbugs has been rather scarce. This review aims at filling this gap. We will describe what are the causes of bacterial resistance and at which level MIPs can deploy their weapons. MIPs' targets can be biofilm constituents, quorum sensing messengers, bacterial surface proteins and antibiotic-deactivating enzymes, among others. We will conclude on the current challenges and future developments in this field.

Host Stress Signals Stimulate Pneumococcal Transition from Colonization to Dissemination into the Lungs

Streptococcus pneumoniae is an asymptomatic colonizer of the nasopharynx, but it is also one of the most important bacterial pathogens of humans, causing a wide range of mild to life-threatening diseases. The basis of the pneumococcal transition from a commensal to a parasitic lifestyle is not fully understood. We hypothesize that exposure to host catecholamine stress hormones is important for this transition. In this study, we demonstrated that pneumococci preexposed to a hormone released during stress, norepinephrine (NE), have an increased capacity to translocate from the nasopharynx into the lungs compared to untreated pneumococci. Examination of NE-treated pneumococci revealed major alterations in metabolic profiles, cell associations, capsule synthesis, and cell size. By systemically mutating all 12 two-component and 1 orphan regulatory systems, we also identified a unique genetic regulatory circuit involved in pneumococcal recognition and responsiveness to human stress hormones. IMPORTANCE Microbes acquire unique lifestyles under different environmental conditions. Although this is a widespread occurrence, our knowledge of the importance of various host signals and their impact on microbial behavior is not clear despite the therapeutic value of this knowledge. We discovered that catecholamine stress hormones are the host signals that trigger the passage of Streptococcus pneumoniae from a commensal to a parasitic state. We identify that stress hormone treatment of this microbe leads to reductions in cell size and capsule synthesis and renders it more able to migrate from the nasopharynx into the lungs in a mouse model of infection. The microbe requires the TCS09 protein for the recognition and processing of stress hormone signals. Our work has particular clinical significance as catecholamines are abundant in upper respiratory fluids as well as being administered therapeutically to reduce inflammation in ventilated patients, which may explain why intubation in the critically ill is a recognized risk factor for the development of pneumococcal pneumonia.

Heterocyclic Chemistry Applied to the Design of N-Acyl Homoserine Lactone Analogues as Bacterial Quorum Sensing Signals Mimics

N-acyl homoserine lactones (AHLs) are small signaling molecules used by many Gram-negative bacteria for coordinating their behavior as a function of their population density. This process, based on the biosynthesis and the sensing of such molecular signals, and referred to as Quorum Sensing (QS), regulates various gene expressions, including growth, virulence, biofilms formation, and toxin production. Considering the role of QS in bacterial pathogenicity, its modulation appears as a possible complementary approach in antibacterial strategies. Analogues and mimics of AHLs are therefore biologically relevant targets, including several families in which heterocyclic chemistry provides a strategic contribution in the molecular design and the synthetic approach. AHLs consist of three main sections, the homoserine lactone ring, the central amide group, and the side chain, which can vary in length and level of oxygenation. The purpose of this review is to summarize the contribution of heterocyclic chemistry in the design of AHLs analogues, insisting on the way heterocyclic building blocks can serve as replacements of the lactone moiety, as a bioisostere for the amide group, or as an additional pattern appended to the side chain. A few non-AHL-related heterocyclic compounds with AHL-like QS activity are also mentioned.

The search for novel treatment strategies for Streptococcus pneumoniae infections

This review provides an overview of the most important novel treatment strategies against Streptococcus pneumoniae infections published over the past 10 years. The pneumococcus causes the majority of community-acquired bacterial pneumonia cases, and it is one of the prime pathogens in bacterial meningitis. Over the last 10 years, extensive research has been conducted to prevent severe pneumococcal infections, with a major focus on (i) boosting the host immune system and (ii) discovering novel antibacterials. Boosting the immune system can be done in two ways, either by actively modulating host immunity, mostly through administration of selective antibodies, or by interfering with pneumococcal virulence factors, thereby supporting the host immune system to effectively overcome an infection. While several of such experimental therapies are promising, few have evolved to clinical trials. The discovery of novel antibacterials is hampered by the high research and development costs versus the relatively low revenues for the pharmaceutical industry. Nevertheless, novel enzymatic assays and target-based drug design, allow the identification of targets and the development of novel molecules to effectively treat this life-threatening pathogen.

Near-infrared light II - assisted rapid biofilm elimination platform for bone implants at mild temperature

Light-triggered therapy is a prospective method to combat implant-associated infection but near-infrared I (NIR-I) light has insufficient penetrating ability in tissues and local hyperthermia induced by the photothermal treatment may destroy surrounding healthy tissues. Herein, a near-infrared II (NIR-II) phototherapy system composed of upconversion elements doped titanium dioxide nanorods (TiO₂ NRs)/curcumin (Cur)/hyaluronic acid (HA)/bone morphogenetic protein-2 (BMP-2) is designed for biomedical titanium and demonstrated to overcome the above hurdles simultaneously. Incorporation of F, Yb, and Ho not only improves the photocatalytic ability, but also renders the implants with the upconversion capability, so that the NRs can generate enough reactive oxygen species (ROS) when irradiated by the NIR-II laser. Furthermore, the combined actions of quorum sensing inhibitors, ROS, and physical puncture by NRs eliminate Staphylococcus aureus biofilms on titanium rapidly at a mild temperature of 45 °C by only requiring irradiation with the 1060 nm laser for only 15 min in vitro and in vivo. The presence of Cur mitigates the immune response and BMP-2 improves osteogenic differentiation, thus accelerating new bone formation. This low-temperature NIR-II light-triggered antibacterial platform has large potential in combating deep-tissue infection in clinical applications.

The pneumococcal social network

Gram-positive bacteria employ an array of secreted peptides to control population-level behaviors in response to environmental cues. We review mechanistic and functional features of secreted peptides produced by the human pathogen Streptococcus pneumoniae. We discuss sequence features, mechanisms of transport, and receptors for 3 major categories of small peptides: the double-glycine peptides, the Rap, Rgg, NprR, PlcR, and PrgX (RRNPP)-binding peptides, and the lanthionine-containing peptides. We highlight the impact of factors that contribute to carriage and pathogenesis, specifically genetic diversity, microbial competition, biofilm development, and environmental adaptation. A recent expansion in pneumococcal peptide studies reveals a complex network of interacting signaling systems where multiple peptides are integrated into the same signaling pathway, allowing multiple points of entry into the pathway and extending information content in new directions. In addition, since peptides are present in the extracellular milieu, there are opportunities for crosstalk, quorum sensing (QS), as well as intra- and interstrain and species interactions. Knowledge on the manner that population-level behaviors contribute to disease provides an avenue for the design and development of anti-infective strategies.

A Portable Visual Sensor by Molecularly Imprinted Hydrogels for HRP Recognition

Background:

Molecular imprinting is a technology used to produce artificial receptors that simulate the molecular recognition in the nature and prepare the polymer network structure in the presence of template molecule. Molecularly imprinted visual sensor combines the advantages of specific recognition via molecular imprinting and fast response speed via visualization. The aims of this paper are to prepare a portable visual sensor for Horseradish Peroxidase (HRP) recognition based on molecularly imprinted hydrogel.

Methods:

At first, HRP-imprinted polyacrylamide hydrogels with 1 mm thickness were obtained by one-step synthesis via radical induced in-situ polymerization of acrylamide using acrylamide (AAm) as the functional monomer, N,N'-Methylenebisacrylamide (MBA) as the crosslink agent and HRP as the template molecule.

Results:

Compared with nonimprinted hydrogels, the HRP-imprinted hydrogel sensor showed significant color changes in response to the target HRP. This visual sensor was constructed based on 3, 3', 5, 5'- tetramethyl benzidine (TMB) - H2O2 color reaction system by HRP catalyzing to produce color change through digital photography and image analysis (RGB system). The HRP-imprinted hydrogel showed good response in the range of 0.001-0.5 mg/mL and had a significant specific recognition compared to other proteins via selective test.

Conclusion:

The proposed portable visual sensor could be used for qualitative and semi-quantitative analysis of HRP with high selectivity and reasonable regeneration. The sensor has the advantages of simple operation, low cost, no special equipment, and can be applied to serum sample with less sample consumption and no need of sample preparation. It has wide application prospects in microfluidic devices, biomimetic sensors, flexible biosensor and membrane separation technology.

In vitro and in vivo Evaluation of in silico Predicted Pneumococcal UDPG:PP Inhibitors

Pneumonia, of which Streptococcus pneumoniae is the most common causative agent, is considered one of the three top leading causes of death worldwide. As seen in other bacterial species, antimicrobial resistance is on the rise for this pathogen. Therefore, there is a pressing need for novel antimicrobial strategies to combat these infections. Recently, uridine diphosphate glucose pyrophosphorylase (UDPG:PP) has been put forward as a potential drug target worth investigating. Moreover, earlier research demonstrated that streptococci lacking a functional galU gene (encoding for UDPG:PP) were characterized by significantly reduced in vitro and in vivo virulence. Therefore, in this study we evaluated the anti-virulence activity of potential UDPG:PP inhibitors. They were selected in silico using a tailor-made streptococcal homology model, based on earlier listerial research. While the compounds didn’t affect bacterial growth, nor affected in vitro adhesion to and phagocytosis in macrophages, the amount of polysaccharide capsule was significantly reduced after co-incubation with these inhibitors. Moreover, co-incubation proved to have a positive effect on survival in an in vivo Galleria mellonella larval infection model. Therefore, rather than targeting bacterial survival directly, these compounds proved to have an effect on streptococcal virulence by lowering the amount of polysaccharide and thereby probably boosting recognition of this pathogen by the innate immune system. While the compounds need adaptation to broaden their activity to more streptococcal strains rather than being strain-specific, this study consolidates UDPG:PP as a potential novel drug target.

Molecularly Imprinted Polymers for Cell Recognition

Since their conception 50 years ago, molecularly imprinted polymers (MIPs) have seen extensive development both in terms of synthetic routes and applications. Cells are perhaps the most challenging target for molecular imprinting. Although early work was based almost entirely around microprinting methods, recent developments have shifted towards epitope imprinting to generate MIP nanoparticles (NPs). Simultaneously, the development of techniques such as solid phase MIP synthesis has solved many historic issues of MIP production. This review briefly describes various approaches used in cell imprinting with a focus on applications of the created materials in imaging, drug delivery, diagnostics, and tissue engineering.

TprA/PhrA Quorum Sensing System Has a Major Effect on Pneumococcal Survival in Respiratory Tract and Blood, and Its Activity Is Controlled by CcpA and GlnR

Streptococcus pneumoniae is able to cause deadly diseases by infecting different tissues, each with distinct environmental and nutritional compositions. We hypothesize that the adaptive capabilities of the microbe is an important facet of pneumococcal survival in fluctuating host environments. Quorum-sensing (QS) mechanisms are pivotal for microbial host adaptation. We previously demonstrated that the TprA/PhrA QS system is required for pneumococcal utilization of galactose and mannose, neuraminidase activity, and virulence. We also showed that the system can be modulated by using linear molecularly imprinted polymers. Due to being a drugable target, we further studied the operation of this QS system in S. pneumoniae. We found that TprA controls the expression of nine different operons on galactose and mannose. Our data revealed that TprA expression is modulated by a complex regulatory network, where the master regulators CcpA and GlnR are involved in a sugar dependent manner. Mutants in the TprA/PhrA system are highly attenuated in their survival in nasopharynx and lungs after intranasal infection, and growth in blood after intravenous infection.

Functional assessment of microbial superoxide dismutase isozymes suggests a differential role for each isozyme

Microbes can have multiple enzymes that are able to catalyse the same enzymatic reactions but may differ in structure. These are known as isozymes. It is assumed that isozymes have the same functional role for cells. Contrary to this assumption, we hypothesised that isozymes can confer different functions for microbial cells despite catalysing the same reactions. To test this hypothesis, we studied the role of superoxide dismutases (SOD) in Klebsiella pneumoniae, the causative agent of several nosocomial and community-acquired infections, in infection relevant assays. SODs are responsible for detoxification of toxic superoxide radicals. K. pneumoniae genome contains three superoxide dismutase genes, sodA, sodB, and sodC coding for Mn-, Fe- and CuZn- co-factored SODs, respectively. By creating and testing single, double, and triple SOD mutants, we investigated the regulatory interactions among SOD and determined the role of each isozyme in oxidative stress resistance, biofilm formation, cell morphology, metabolism, and in vivo colonization and persistence. Our results demonstrate that SOD isozymes in K. pneumoniae have unique roles beyond oxidative stress resistance, and there is a regulatory interplay among SODs.

Application of molecularly imprinted polymer nanoparticles for degradation of the bacterial autoinducer N-hexanoyl homoserine lactone

A novel bacterial quorum quenching system is presented. For the first time the degradation of N-l-hexanoyl homoserine lactone (C6-AHL), a Gram-negative quorum sensing autoinducer, has been enhanced using molecularly imprinted nanoparticles (MIP NPs) which were prepared using transition state analogue of the γ-lactone ring hydrolysis as template.

Synthetic nanoparticles for selective hydrolysis of bacterial autoinducers in quorum sensing

N-acyl homoserine lactones (AHLs) are signal molecules used by a large number of gram-negative bacteria in quorum sensing and their hydrolysis is known to inhibit biofilm formation. Micellar imprinting of AHL-like templates with catalytic functional monomers yielded water-soluble nanoparticles with AHL-shaped active site and nearby catalytic groups. Either Lewis acidic zinc ions or nucleophilic pyridyl ligands could be introduced through this strategy, yielding artificial enzymes for the hydrolysis of AHLs in a substrate-selective fashion.