Solution-Mediated Modulation of Pseudomonas aeruginosa Biofilm Formation by a Cationic Synthetic Polymer

Inflammatory Microenvironment-Responsive Hydrogels Enclosed with Quorum Sensing Inhibitor for Treating Post-Traumatic Osteomyelitis

Non-antibiotic strategies are desperately needed to treat post-traumatic osteomyelitis (PTO) due to the emergence of superbugs, complex inflammatory microenvironments, and greatly enriched biofilms. Previously, growing evidence indicated that quorum sensing (QS), a chemical communication signal among bacterial cells, can accelerate resistance under evolutionary pressure. This study aims to develop a medical dressing to treat PTO by inhibiting QS and regulating the inflammatory microenvironment, which includes severe oxidative stress and acid abscesses, through a reactive oxygen species (ROS)-responsive bond between N1- (4-borobenzoyl)-N3-(4-borobenzoyl)-the N1, the N1, N3, N3-tetramethylpropane-1,3-diamine (TSPBA) and polyvinyl alcohol (PVA), and the amino side chain of hyperbranched polylysine (HBPL). Physically enclosed QS inhibitors subsequently exerted the antibacterial effects. This hydrogel can scavenge hydrogen peroxide (H2O2), superoxide anion free radical (·O2 -), hydroxyl radicals (·OH) and 2,2-di(4-tert-octylphenyl)-1-picryl-hydrazyl (DPPH) to reduce oxidative stress and inhibit "bacteria-to-bacteria communication", thus clearing planktonic bacteria and biofilms, accelerating bacterial plasmolysis, reducing bacterial virulence and interfering with membrane transport. After in vivo treatment with hydrogel, nearly all bacteria are eliminated, inflammation is effectively inhibited, and osteogenesis and bone repair are promoted to facilitate recovery from PTO. The work demonstrates the clinical translational potential of the hydrogel in the treatment of drug-resistant bacteria induced PTO.

Dynamic Antimicrobial Poly(disulfide) Coatings Exfoliate Biofilms On Demand Via Triggered Depolymerization

Bacterial biofilms are notoriously problematic in applications ranging from biomedical implants to ship hulls. Cationic, amphiphilic antibacterial surface coatings delay the onset of biofilm formation by killing microbes on contact, but they lose effectiveness over time due to non-specific binding of biomass and biofilm formation. Harsh treatment methods are required to forcibly expel the biomass and regenerate a clean surface. Here, a simple, dynamically reversible method of polymer surface coating that enables both chemical killing on contact, and on-demand mechanical delamination of surface-bound biofilms, by triggered depolymerization of the underlying antimicrobial coating layer, is developed. Antimicrobial polymer derivatives based on α-lipoic acid (LA) undergo dynamic and reversible polymerization into polydisulfides functionalized with biocidal quaternary ammonium salt groups. These coatings kill >99.9% of Staphylococcus aureus cells, repeatedly for 15 cycles without loss of activity, for moderate microbial challenges (≈105 colony-forming units (CFU) mL-1, 1 h), but they ultimately foul under intense challenges (≈107 CFU mL-1, 5 days). The attached biofilms are then exfoliated from the polymer surface by UV-triggered degradation in an aqueous solution at neutral pH. This work provides a simple strategy for antimicrobial coatings that can kill bacteria on contact for extended timescales, followed by triggered biofilm removal under mild conditions.

Size-Controlled Ammonium-Based Homopolymers as Broad-Spectrum Antibacterials

Ammonium group containing polymers possess inherent antimicrobial properties, effectively eliminating or preventing infections caused by harmful microorganisms. Here, homopolymers based on monomers containing ammonium groups were synthesized via Reversible Addition Fragmentation Chain Transfer Polymerization (RAFT) and evaluated as potential antibacterial agents. The antimicrobial activity was evaluated against Gram-positive (M. luteus and B. subtilis) and Gram-negative bacteria (E. coli and S. typhimurium). Three polymers, poly(diallyl dimethyl ammonium chloride), poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), and poly(vinyl benzyl trimethylammonium chloride), were examined to explore the effect of molecular weight (10 kDa, 20 kDa, and 40 kDa) on their antimicrobial activity and toxicity to mammalian cells. The mechanisms of action of the polymers were investigated with dye-based assays, while Scanning Electron Microscopy (SEM) showed collapsed and fused bacterial morphologies due to the interactions between the polymers and components of the bacterial cell envelope, with some polymers proving to be bactericidal and others bacteriostatic, while being non-hemolytic. Among all the homopolymers, the most active, non-Gram-specific polymer was poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), with a molecular weight of 40 kDa, with minimum inhibitory concentrations between 16 and 64 µg/mL, showing a bactericidal mode of action mediated by disruption of the cytoplasmic membrane. This homopolymer could be useful in biomedical applications such as surface dressings and in areas such as eye infections.

Investigation of the Role of Hydrophobic Amino Acids on the Structure-Activity Relationship in the Antimicrobial Venom Peptide Ponericin L1

Venom mixtures from insects, reptiles, and mollusks have long been a source of bioactive peptides which often have alternative uses as therapeutics. While these molecules act in numerous capacities, there have been many venom components that act on the target cells through membrane disruptive mechanisms. These peptides have long been of interest as potential antimicrobial peptide platforms, but the inherent cytotoxicity of venom peptides often results in poor therapeutic potential. Despite this, efforts are ongoing to identify and characterize venom peptide which exhibit high antimicrobial activity with low cytotoxicity and modify these to further enhance the efficacy while reducing toxicity. One example is ponericin L1 from Neoponera goeldii which has been demonstrated to have good antimicrobial activity and low in vitro cytotoxicity. The L1 sequence was modified by uniformly replacing the native hydrophobic residues with either Leu, Ile, Phe, Ala, or Val. Spectroscopic and microbiological approaches were employed to investigate how the amino acid sequence changes impacted membrane interaction, secondary structure, and antimicrobial efficacy. The L1 derivatives showed varying degrees of bilayer interaction, in some cases driven by bilayer composition. Several of the variants exhibited enhanced antimicrobial activity compared to the parent strain, while others lost all activity. Interestingly, the variant containing Val lost all antimicrobial activity and ability to interact with bilayers. Taken together the results indicate that peptide secondary structure, amino acid composition, and hydrophobicity all play a role in peptide activity, although this is a delicate balance that can result in non-specific binding or complete loss of activity if specific amino acids are incorporated.

Bacterial aggregation assisted by anionic surfactant and calcium ions

We identify factors leading to aggregation of bacteria in the presence of a surfactant using absorbance and microscopy. Two marine bacteria, Marinobacter hydrocarbonoclasticus SP17 and Halomonas titanicae Bead 10BA, formed aggregates of a broad size distribution in synthetic sea water in the presence of an anionic surfactant, dioctyl sodium sulfosuccinate (DOSS). Both DOSS at high concentrations and calcium ions were necessary for aggregate formation, but DOSS micelles were not required for aggregation. Addition of proteinase K but not DNase1 eliminated aggregate formation over two hours. Finally, swimming motility also enhanced aggregate formation.

Screening and Matching Amphiphilic Cationic Polymers for Efficient Antibiosis

The amphiphilic cationic polymers that mimic antimicrobial peptides have received increasing attention due to their excellent antibacterial activity. However, the relationship between the structure of cationic polymers and its antibacterial effect remains unclear. In our current work, a series of PEG blocked amphiphilic cationic polymers composed of hydrophobic alkyl-modified and quaternary ammonium salt (QAS) moieties have been prepared. The structure-antibacterial activity relationship of these cationic polymers was investigated against E. coli and S. aureus, including PEGylation, random structure, molecular weights, and the content and lengths of the hydrophobic alkyl side chains. The results indicated that PEGylated random amphiphilic cationic copolymer (mPB₃₅/T₅₇) showed stronger antibacterial activity and better biocompatibility than the random copolymer without PEG (PB₃₃/T₅₆). Furthermore, mPB₃₅/T₅₇ with appropriate mole fraction of alkyl side chains (f_alkyl = 0.38), degree of polymerization (DP = 92), and four-carbon hydrophobic alkyl moieties was found to have the optimal structure that revealed the best antibacterial activities against both E. coli (MIC = 8 μg/mL, selectivity > 250) and S. aureus (MIC = 4 μg/mL, selectivity > 500). More importantly, mPB₃₅/T₅₇ could effectively eradicate E. coli biofilms by killing the bacteria embedded in the biofilms. Therefore, the structure of mPB₃₅/T₅₇ provided valuable information for improving the antibacterial activity of cationic polymers.

Leveraging Stereoelectronic Effects in Biofilm Eradication: Synthetic β-Amino Human Milk Oligosaccharides Impede Microbial Adhesion As Observed by Scanning Electron Microscopy

Alongside Edward, Lemieux was among the earliest researchers studying negative hyperconjugation (i.e., the anomeric effect) or the preference for gauche conformations about the C1-O5 bond in carbohydrates. Lemieux also studied an esoteric, if not controversial, theory known as the reverse anomeric effect (RAE). This theory is used to rationalize scenarios where predicted anomeric stabilization does not occur. One such example is the Kochetkov amination where reducing end amines exist solely as the β-anomer. Herein, we provide a brief account of Lemieux's contributions to the field of stereoelectronics and apply this knowledge toward the synthesis of β-amino human milk oligosaccharides (βΑ-HMOs). These molecules were evaluated for their ability to inhibit growth and biofilm production in Group B Streptococcus (GBS) and Staphylococcus aureus. While the parent HMOs lacked antimicrobial and antibiofilm activity, their β-amino derivatives significantly inhibited biofilm formation in both species. Field emission gun-scanning single electron microscopy (FEG-SEM) revealed that treatment with β-amino HMOs significantly inhibits bacterial adherence and eliminates the ability of both microbes to form biofilms.

An Inactive Dispersin B Probe for Monitoring PNAG Production in Biofilm Formation

The bacterial exopolysaccharide poly-β-1,6-N-acetylglucosamine is a major extracellular matrix component in biofilms of both Gram-positive and Gram-negative organisms. We have leveraged the specificity of the biofilm-dispersing glycoside hydrolase Dispersin B (DspB) to generate a probe (Dispersin B PNAG probe, DiPP) for monitoring PNAG production and localization during biofilm formation. Mutation of the active site of Dispersin B gave DiPP, which was an effective probe despite its low affinity for PNAG oligosaccharides (K_D ∼ 1-10 mM). Imaging of PNAG-dependent and -independent biofilms stained with a fluorescent-protein fusion of DiPP (GFP-DiPP) demonstrated the specificity of the probe for the structure of PNAG on both single-cell and biofilm levels, indicating a high local concentration of PNAG at the bacterial cell surface. Through quantitative bacterial cell binding assays and confocal microscopy analysis using GFP-DiPP, discrete areas of local high concentrations of PNAG were detected on the surface of early log phase cells. These distinct areas were seen to grow, slough from cells, and accumulate in interbacterial regions over the course of several cell divisions, showing the development of a PNAG-dependent biofilm. A potential helical distribution of staining was also noted, suggesting some degree of organization of PNAG production at the cell surface prior to cell aggregation. Together, these experiments shed light on the early stages of PNAG-dependent biofilm formation and demonstrate the value of a low-affinity-high-specificity probe for monitoring the production of bacterial exopolysaccharides.