Self-assembly of lipopolysaccharide layers on allantoin crystals

Automated sepsis detection with vancomycin- and allantoin-polydopamine magnetic nanoparticles

Rapid and accurate identification of the bacteria responsible for sepsis is paramount for effective patient care. Molecular diagnostic methods, such as polymerase chain reaction (PCR), encounter challenges in sepsis due to inhibitory compounds in the blood, necessitating their removal for precise analysis. In this study we present an innovative approach that utilizes vancomycin (Van) and allantoin (Al)-conjugated polydopamine (PDA)-coated magnetic nanoparticles (MNPs) for the rapid and automated enrichment of bacteria and their DNA extraction from blood without inducing clumping and aggregation of blood. Al/Van-PDA-MNPs, facilitated by IMS, eliminate the need for preliminary sample treatments, providing a swift and efficient method for bacterial concentration and DNA extraction within an hour. Employing Al/Van-PDA-MNPs within an automated framework has markedly improved our ability to pre-concentrate various Gram-negative and Gram-positive bacteria directly from blood samples. This advancement has effectively reduced the detection threshold to 102 colony-forming unit/mL by both PCR and quantitative PCR. The method's expedited processing time, combined with its precision, positions it as a feasible diagnostic tool for diverse healthcare settings, ranging from small clinics to large hospitals. Furthermore, the innovative application of nanoparticles for DNA extraction holds promising potential for advancing sepsis diagnostics, enabling earlier interventions and improving patient outcomes.

Verification of a method using magnetic bead enrichment and nucleic acid extraction to improve the molecular detection of bacterial contamination in blood components

Bacterial contamination of blood products poses a significant risk in transfusion medicine. Platelets are particularly vulnerable to bacterial growth because they must be stored at room temperature with constant agitation for >5 days. The limitations of bacterial detection using conventional methods, such as blood cultures and lateral flow assays, include the long detection times, low sensitivity, and the requirement for substantial volumes of blood components. To address these limitations, we assessed the performance of a bacterial enrichment technique using antibiotic-conjugated magnetic nanobeads (AcMNBs) and real-time PCR for the detection of bacterial contamination in plasma. AcMNBs successfully captured >80% of four bacterial strains, including Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Klebsiella pneumoniae, in both plasma and phosphate-buffered saline. After 24-h incubation with bacterial enrichment, S. aureus and B. cereus were each detected at 101 CFU/mL in all trials (5/5), E. coli at 101 CFU/mL in 1/5 trials, and K. pneumoniae at 10² CFU/mL in 4/5 trials. Additionally, without incubation, the improvement was also achieved in samples with bacterial enrichment, S. aureus at 10² CFU/mL and B. cereus at 101 CFU/mL in 1/5 trials each, E. coli at 10³ CFU/mL in 3/5 trials, and K. pneumoniae at 10¹ CFU/mL in 2/5 trials. Overall, the findings from this study strongly support the superiority of bacterial enrichment in detecting low-level bacterial contamination in plasma when employing AcMNBs and PCR.IMPORTANCEThe study presents a breakthrough approach to detect bacterial contamination in plasma, a critical concern in transfusion medicine. Traditional methods, such as blood cultures and lateral flow assays, are hampered by slow detection times, low sensitivity, and the need for large blood sample volumes. Our research introduces a novel technique using antibiotic-conjugated magnetic nanobeads combined with real-time PCR, enhancing the detection of bacteria in blood products, especially platelets. This method has shown exceptional efficiency in identifying even low levels of four different species of bacteria in plasma. The ability to detect bacterial contamination rapidly and accurately is vital for ensuring the safety of blood transfusions and can significantly reduce the risk of infections transmitted through blood products. This advancement is a pivotal step in improving patient outcomes and elevating the standards of care in transfusion medicine.

Non-Affinity Purification of Antibodies

Currently, purification of antibodies is mainly carried out using a platform technology composed primarily of Protein A chromatography as a capture step, regardless of the scale. However, Protein A chromatography has a number of drawbacks, which are summarized in this review. As an alternative, we propose a simple small-scale purification protocol without Protein A that uses novel agarose native gel electrophoresis and protein extraction. For large-scale antibody purification, we suggest mixed-mode chromatography that can in part mimic the properties of Protein A resin, focusing on 4-Mercapto-ethyl-pyridine (MEP) column chromatography.

Molecular detection of bacterial contamination in plasma using magnetic-based enrichment

Bacterial contamination of blood products is a major problem in transfusion medicine, in terms of both morbidity and mortality. Platelets (PLTs) are stored at room temperature (under constant agitation) for more than 5 days, and bacteria can thus grow significantly from a low level to high titers. However, conventional methods like blood culture and lateral flow assay have disadvantages such as long detection time, low sensitivity, and the need for a large volume of blood components. We used real-time polymerase chain reaction (PCR) assays with antibiotic-conjugated magnetic nanobeads (MNBs) to detect enriched Gram-positive and -negative bacteria. The MNBs were coated with polyethylene glycol (PEG) to prevent aggregation by blood components. Over 80% of all bacteria were captured by the MNBs, and the levels of detection were 10¹ colony forming unit [CFU]/mL and 10² CFU/mL for Gram-positive and -negative bacteria, respectively. The detection time is < 3 h using only small volumes of blood components. Thus, compared to conventional methods, real-time PCR using MNBs allows for rapid detection with high sensitivity using only a small volume of blood components.

Physically Crosslinked Chitosan/PVA Hydrogels Containing Honey and Allantoin with Long-Term Biocompatibility for Skin Wound Repair: An In Vitro and In Vivo Study

Chitosan/PVA hydrogel films crosslinked by the freeze-thaw method and containing honey and allantoin were prepared for application as wound dressing materials. The effects of the freeze-thaw process and the addition of honey and allantoin on the swelling, the gel content and the mechanical properties of the samples were evaluated. The physicochemical properties of the samples, with and without the freeze-thaw process, were compared using FTIR, DSC and XRD. The results showed that the freeze-thaw process can increase the crystallinity and thermal stability of chitosan/PVA films. The freeze-thaw process increased the gel content but did not have a significant effect on the tensile strength. The presence of honey reduced the swelling and the tensile strength of the hydrogels due to hydrogen bonding interactions with PVA and chitosan chains. Long-term cell culture experiments using normal human dermal fibroblast (NHDF) cells showed that the hydrogels maintained their biocompatibility, and the cells showed extended morphology on the surface of the hydrogels for more than 30 days. The presence of honey significantly increased the biocompatibility of the hydrogels. The release of allantoin from the hydrogel was studied and, according to the Korsmeyer-Peppas and Weibull models, the mechanism was mainly diffusional. The results for the antimicrobial activity against E. coli and S. aureus bacteria showed that the allantoin-containing samples had a more remarkable antibacterial activity against S. aureus. According to the wound healing experiments, 98% of the wound area treated by the chitosan/PVA/honey hydrogel was closed, compared to 89% for the control. The results of this study suggest that the freeze-thaw process is a non-toxic crosslinking method for the preparation of chitosan/PVA hydrogels with long term biocompatibility that can be applied for wound healing and skin tissue engineering.

Interactions between Mutant Bacterial Lipopolysaccharide (LPS-Ra) Surface Layers: Surface Vesicles, Membrane Fusion, and Effect of Ca2+and Temperature

Lipopolysaccharides (LPS) are a major component of the protective outer membrane of Gram-negative bacteria. Understanding how the solution conditions may affect LPS-containing membranes is important to optimizing the design of antibacterial agents (ABAs) which exploit electrostatic and hydrophobic interactions to disrupt the bacteria membrane. Here, interactions between surface layers of LPS (Ra mutants) in aqueous media have been studied using a surface force apparatus (SFA), exploring the effects of temperature and divalent Ca²⁺ cations. Complementary dynamic light scattering (DLS) characterization suggests that vesicle-like aggregates of diameter ∼28-80 nm are formed by LPS-Ra in aqueous media. SFA results show that LPS-Ra vesicles adsorb weakly onto mica in pure water at room temperature (RT) and the surface layers are readily squeezed out as the two surfaces approach each other. However, upon addition of calcium (Ca²⁺) cations at near physiological concentration (2.5 mM) at RT, LPS multilayers or deformed LPS liposomes on mica are observed, presumably due to bridging between LPS phosphate groups and between LPS phosphates and negatively charged mica mediated by Ca²⁺, with a hard wall repulsion at surface separation D₀ ∼ 30-40 nm. At 40 °C, which is above the LPS-Ra β-α acyl chain melting temperature (T_m = 36 °C), fusion events between the surface layers under compression could be observed, evident from δD ∼ 8-10 nm steps in the force-distance profiles attributed to LPS-bilayers being squeezed out due to enhanced fluidity of the LPS acyl-chain, with a final hard wall surface separation D₀ ∼ 8-10 nm corresponding to the thickness of a single bilayer confined between the surfaces. These unprecedented SFA results reveal intricate structural responses of LPS surface layers to temperature and Ca²⁺, with implications to our fundamental understanding of the structures and interactions of bacterial membranes.

Effects of allantoin and dimethyl sulfoxide on the thermal aggregation of lysozyme

Allantoin is used to suppress protein aggregation without decreasing the melting temperature. However, the solubility of allantoin in water or buffer solutions is too low (approximately 30 mM at ambient temperature) to be used as a protein aggregation suppressor in various situations. Here we show that a high-concentration solution of allantoin in neat dimethyl sulfoxide (DMSO) is useful as a stock solution for the additive that controls protein aggregation. The allantoin concentration from 10 to 100 mM in 10% (v/v) DMSO significantly suppressed the thermal aggregation of hen egg white lysozyme as a model protein, with increasing allantoin concentration. The residual activity of lysozyme in 10% DMSO and 100 mM allantoin after heating at 90 °C for 10 min was increased >3-fold compared to that without allantoin. Thus, it was concluded that allantoin in DMSO is an effective stock solution for practical application in enhancing the recovery of enzymatic activity and suppressing the formation of small aggregate of protein.

Allantoin and hydantoin as new protein aggregation suppressors

Allantoin is widely used in pharmaceutical and cosmetic products, and is composed of a hydantoin ring and a ureido group. Recent reports showed that allantoin suppresses thermal aggregation of hen egg white lysozyme (LYZ). However, structural insight into the properties of allantoin on protein aggregation and whether allantoin controls the aggregation of other proteins under different stress conditions remain unclear. Here we studied the structural properties of allantoin in terms of its effects on protein aggregation by comparing allantoin with urea and hydantoin. Furthermore, we analyzed the effects of allantoin and its derivatives on the aggregation of LYZ, carbonic anhydrase from bovine erythrocytes (BCA), albumin from chicken egg white (OVA), and immunoglobulin G (IgG) by various stresses in comparison with arginine. These four proteins are widely different in charged state and molecular size. Allantoin suppressed the aggregation and inactivation of LYZ comparing to arginine without affecting the melting temperature of proteins, and was responsible for the slightly improved formation of soluble oligomers and insoluble aggregates of IgG with thermal and acidic stresses. In contrast, hydantoin increased the solubility of aromatic amino acids more effectively than arginine and allantoin. The structural properties underlying the observed effects of allantoin as an aggregation suppressor include hydrophobic interactions between hydantoin moiety and aromatic ring on the surface of proteins, which is reflected on the difference between allantoin and arginine. These results show that the backbone of hydantoin ring may be a new category of additives for development of small aggregation suppressors.

Design of bio-molecular interfaces using liquid crystals demonstrating endotoxin interactions with bacterial cell wall components

Liquid crystals offer a promising approach to study and quantify the interactions between different bacterial cell membrane components with endotoxin at an aqueous interface.