Fluorescence Imaging of Streptococcus pneumoniae with the Helix pomatia agglutinin (HPA) As a Potential, Rapid Diagnostic Tool

Phosphorylcholine esterase is critical for Dolichos biflorus and Helix pomatia agglutinin binding to pneumococcal teichoic acid

Streptococcus pneumoniae (the pneumococcus) has wall teichoic acid (WTA) and lipoteichoic acid (LTA) expressing the Forssman antigen (FA). Two lectins, Dolichos biflorus agglutinin (DBA) and Helix pomatia agglutinin (HPA), are known to bind FA. To determine the molecular structure targeted by these two lectins, different pneumococcal strains were studied for DBA/HPA binding with flow cytometry and fluorescence microscopy. Genetic experiments were used to further examine the lectins' molecular target. Twelve strains were positive for DBA binding, whereas three were negative. Super-resolution microscopy showed that DBA stained only the subcapsular area of pneumococci. The three DBA nonbinders showed no phosphorylcholine esterase (Pce) activity in vitro, whereas 10 DBA binders displayed Pce activity (the remaining two strains were DBA binders with no Pce activity in vitro). The pcegene sequence for 10 representative strains revealed two functional pce alleles, the previously recognized "allele A" and a newly discovered "allele B" (with 12 additional nucleotides). Isolates with allele B showed no Pce activity in vitro but did bind to DBA, indicating allele B Pce is functional in vivo. Genetic transfer experiments confirmed that either allele is sufficient (and necessary) for DBA binding. The three DBA nonbinders had various mutations that affected Pce function. Observations with HPA were identical to those with DBA. We show that DBA and HPA bind only to the WTA/LTA of pneumococcal isolates with a functional Pce enzyme. A newly discovered Pce variant (allele B) is functional in vivo but nonfunctional when assayed in vitro.

H-type lectins - Structural characteristics and their applications in diagnostics, analytics and drug delivery

Lectins are ubiquitous carbohydrate-binding proteins that interact with sugar moieties in a highly specific manner. H-type lectins represent a new group of lectins that were identified in invertebrates. These lectins share structural homology and bind mainly to N-acetylgalactosamine (GalNAc). Recent structural studies on the H-type lectins provided a detailed description of the GalNAc-lectin interaction that is already exploited in a number of biomedical applications. Two members of the H-type lectin family, Helix pomatia agglutinin (HPA) and Helix aspersa agglutinin (HAA), have already been extensively used in many diagnostic tests due their ability to specifically recognize GalNAc. This ability is especially important because aberrant glycosylation patterns of proteins expressed by cancer cells contain GalNAc. In addition, H-type lectins were utilized in diagnostics of other non-cancer diseases and represent great potential as components of drug delivery systems. Here, we present an overview of the H-type lectins and their applications in diagnostics, analytics and drug delivery.

Comprehensive evaluation of chitosan nanoparticle based phage lysin delivery system; a novel approach to counter S. pneumoniae infections

Cpl-1, an endolysin derived from Cp-1 phage has been found to be effective in a number of in-vitro and in-vivo pneumococcal infection models. However its lower bioavailability under in-vivo conditions limits its applicability as therapeutic agent. In this study, Cpl-1 loaded chitosan nanoparticles were set up in order to develop a novel therapeutic delivery system to counter antibiotic resistant S. pneumoniae infections. Interactions of chitosan and Cpl-1 were studied by in-silico docking analysis. Chitosan nanoparticles and Cpl-1 loaded chitosan nanoparticles were prepared by using ionic gelation method and the process was optimized by varying chitosan:TPP ratio, pH, stirring time, stirring rate and Cpl-1 concentration. Chitosan nanoparticles and Cpl-1 loaded chitosan nanoparticles were characterized to ascertain successful formation of nanoparticles and entrapment of Cpl-1 into nanoparticles. Chitosan nanoparticles and Cpl-1 loaded nanoparticles were also evaluated for nanoparticle yield, entrapment efficiency, in-vitro release, stability, structural integrity of Cpl-1, in-vitro bioassay, swelling studies, in-vitro biodegradation and heamolysis studies. Mucoadhesion behavior of chitosan nanoparticles and Cpl-1 loaded nanoparticles was explored using mucous glycoprotein assay and ex-vivo mucoadhesion assay, both preparations exhibited their mucoadhesive nature. Cellular cytotoxicity and immune stimulation studies revealed biocompatible nature of nanoparticles. The results of this study confirm that chitosan nanoparticles are a promising biocompatible candidate for Cpl-1 delivery with a significant potential to increase bioavailability of enzyme that in turn can increase its in-vivo half life to treat S. pneumoniae infections.

Widening the antimicrobial spectrum of esters of bicyclic amines: In vitro effect on gram-positive Streptococcus pneumoniae and gram-negative non-typeable Haemophilus influenzae biofilms

Antibiotic resistance is a global current threat of increasing importance. Moreover, biofilms represent a medical challenge since the inherent antibiotic resistance of their producers demands the use of high doses of antibiotics over prolonged periods. Frequently, these therapeutic measures fail, contributing to bacterial persistence, therefore demanding the development of novel antimicrobials. Esters of bicyclic amines (EBAs), which are strong inhibitors of Streptococcus pneumoniae growth, were initially designed as inhibitors of pneumococcal choline-binding proteins on the basis of their structural analogy to the choline residues in the cell wall. However, instead of mimicking the characteristic cell chaining phenotype caused by exogenously added choline on planktonic cultures of pneumococcal cells, EBAs showed an unexpected lytic activity. In this work we demonstrate that EBAs display a second, and even more important, function as cell membrane destabilizers. We then assayed the inhibitory and disintegrating activity of these molecules on pneumococcal biofilms. The selected compound (EBA 31) produced the highest effect on S. pneumoniae (encapsulated and non-encapsulated) biofilms at very low concentrations. EBA 31 was also effective on mixed biofilms of non-encapsulated S. pneumoniae plus non-typeable Haemophilus influenzae, two pathogens frequently forming a self-produced biofilm in the human nasopharynx. These results support the role of EBAs as a promising alternative for the development of novel, broad-range antimicrobial drugs encompassing both Gram-positive and Gram-negative pathogens.