Killing Of Gram-negative Bacteria Research Articles

Triggered Release of Ampicillin from Metallic Implant Coatings for Combating Periprosthetic Infections.

Periprosthetic infections caused by Staphylococcus aureus (S. aureus) pose unique challenges in orthopedic surgeries, in part due to the bacterium's capacity to invade surrounding bone tissues besides forming recalcitrant biofilms on implant surfaces. We previously developed prophylactic implant coatings for the on-demand release of vancomycin, triggered by the cleavage of an oligonucleotide (Oligo) linker by micrococcal nuclease (MN) secreted by the Gram-positive bacterium, to eradicate S. aureus surrounding the implant in vitro and in vivo. Building upon this coating platform, here we explore the feasibility of extending the on-demand release to ampicillin, a broad-spectrum aminopenicillin β-lactam antibiotic that is more effective than vancomycin in killing Gram-negative bacteria that may accompany S. aureus infections. The amino group of ampicillin was successfully conjugated to the carboxyl end of an MN-sensitive Oligo covalently integrated in a polymethacrylate hydrogel coating applied to titanium alloy pins. The resultant Oligo-Ampicillin hydrogel coating released the β-lactam in the presence of S. aureus and successfully cleared nearby S. aureus in vitro. When the Oligo-Ampicillin-coated pin was delivered to a rat femoral canal inoculated with 1000 cfu S. aureus, it prevented periprosthetic infection with timely on-demand drug release. The clearance of the bacteria from the pin surface as well as surrounding tissue persisted over 3 months, with no local or systemic toxicity observed with the coating. The negatively charged Oligo fragment attached to ampicillin upon cleavage from the coating did diminish the antibiotic's potency against S. aureus and Escherichia coli (E. coli) to varying degrees, likely due to electrostatic repulsion by the anionic surfaces of the bacteria. Although the on-demand release of the β-lactam led to adequate killing of S. aureus but not E. coli in the presence of a mixture of the bacteria, strong inhibition of the colonization of the remaining E. coli on hydrogel coating was observed. These findings will inspire considerations of alternative broad-spectrum antibiotics, optimized drug conjugation, and Oligo linker engineering for more effective protection against polymicrobial periprosthetic infections.

Anti-Microbial Activities of Mussel-Derived Recombinant Proteins against Gram-Negative Bacteria.

Many anti-microbial peptides (AMPs) and pro-apoptotic peptides are considered as novel anti-microbial agents, distinguished by their different characteristics. Nevertheless, AMPs exhibit certain limitations, including poor stability and potential toxicity, which hinder their suitability for applications in pharmaceutics and medical devices. In this study, we used recombinant mussel adhesive protein (MAP) as a robust scaffold to overcome these limitations associated with AMPs. Mussel adhesive protein fused with functional peptides (MAP-FPs) was used to evaluate anti-microbial activities, minimal inhibitory concentration (MIC), and time-kill kinetics (TKK) assays against six of bacteria strains. MAP and MAP-FPs were proved to have an anti-microbial effect with MIC of 4 or 8 µM against only Gram-negative bacteria strains. All tested MAP-FPs killed four different Gram-negative bacteria strains within 180 min. Especially, MAP-FP-2 and -5 killed three Gram-negative bacteria strain, including E. coli, S. typhimurium, and K. pneumoniae, within 10 min. A cytotoxicity study using Vero and HEK293T cells indicated the safety of MAP and MAP-FP-2 and -3. Thermal stability of MAP-FP-2 was also validated by HPLC analysis at an accelerated condition for 4 weeks. This study identified that MAP-FPs have novel anti-microbial activity, inhibiting the growth and rapidly killing Gram-negative bacteria strains with high thermal stability and safety.

Vancomycin-Polyguanidino Dendrimer Conjugates Inhibit Growth of Antibiotic-Resistant Gram-Positive and Gram-Negative Bacteria and Eradicate Biofilm-Associated S.aureus.

The global challenge of antibiotic resistance necessitates the introduction of more effective antibiotics. Here we report a potentially general design strategy, exemplified with vancomycin, that improves and expands antibiotic performance. Vancomycin is one of the most important antibiotics in use today for the treatment of Gram-positive infections. However, it fails to eradicate difficult-to-treat biofilm populations. Vancomycin is also ineffective in killing Gram-negative bacteria due to its inability to breach the outer membrane. Inspired by our seminal studies on cell penetrating guanidinium-rich transporters (e.g., octaarginine), we recently introduced vancomycin conjugates that effectively eradicate Gram-positive biofilm bacteria, persister cells and vancomycin-resistant enterococci (with V-r8, vancomycin-octaarginine), and Gram-negative pathogens (with V-R, vancomycin-arginine). Having shown previously that the spatial array (linear versus dendrimeric) of multiple guanidinium groups affects cell permeation, we report here for the first time vancomycin conjugates with dendrimerically displayed guanidinium groups that exhibit superior efficacy and breadth, presenting the best activity of V-r8 and V-R in single broad-spectrum compounds active against ESKAPE pathogens. Mode-of-action studies reveal cell-surface activity and enhanced vancomycin-like killing. The vancomycin-polyguanidino dendrimer conjugates exhibit no acute mammalian cell toxicity or hemolytic activity. Our study introduces a new class of broad-spectrum vancomycin derivatives and a general strategy to improve or expand antibiotic performance through combined mode-of-action and function-oriented design studies.

Distinct mode of action of a highly stable, engineered phage lysin killing Gram-negative bacteria.

Engineered lysins are considered as highly promising alternatives for antibiotics. Our previous screening study using VersaTile technology identified 1D10 as a possible lead compound with activity against Acinetobacter baumannii strains under elevated human serum concentrations. In this manuscript, we reveal an unexpected mode of action and exceptional thermoresistance for lysin 1D10. Our findings shed new light on the development of engineered lysins, providing valuable insights for future research in this field.

Enhancement of β-Lactam-Mediated Killing of Gram-Negative Bacteria by Lysine Hydrochloride.

Widespread bacterial resistance among Gram-negative bacteria is rapidly depleting our antimicrobial arsenal. Adjuvants that enhance the bactericidal activity of existing antibiotics provide a way to alleviate the resistance crisis, as new antimicrobials are becoming increasingly difficult to develop. The present work with Escherichia coli revealed that neutralized lysine (lysine hydrochloride) enhances the bactericidal activity of β-lactams in addition to increasing bacteriostatic activity. When combined, lysine hydrochloride and β-lactam increased expression of genes involved in the tricarboxylic acid (TCA) cycle and raised reactive oxygen species (ROS) levels; as expected, agents known to mitigate bactericidal effects of ROS reduced lethality from the combination treatment. Lysine hydrochloride had no enhancing effect on the lethal action of fluoroquinolones or aminoglycosides. Characterization of a tolerant mutant indicated involvement of the FtsH/HflkC membrane-embedded protease complex in lethality enhancement. The tolerant mutant, which carried a V86F substitution in FtsH, exhibited decreased lipopolysaccharide levels, reduced expression of TCA cycle genes, and reduced levels of ROS. Lethality enhancement by lysine hydrochloride was abolished by treating cultures with Ca2+ or Mg2+, cations known to stabilize the outer membrane. These data, plus damage observed by scanning electron microscopy, indicate that lysine stimulates β-lactam lethality by disrupting the outer membrane. Lethality enhancement of β-lactams by lysine hydrochloride was also observed with Acinetobacter baumannii and Pseudomonas aeruginosa, thereby suggesting that the phenomenon is common among Gram-negative bacteria. Arginine hydrochloride behaved in a similar way. Overall, the combination of lysine or arginine hydrochloride and β-lactam offers a new way to increase β-lactam lethality with Gram-negative pathogens. IMPORTANCE Antibiotic resistance among Gram-negative pathogens is a serious medical problem. The present work describes a new study in which a nontoxic nutrient increases the lethal action of clinically important β-lactams. Elevated lethality is expected to reduce the emergence of resistant mutants. The effects were observed with significant pathogens (Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa), indicating widespread applicability. Examination of tolerant mutants and biochemical measurements revealed involvement of endogenous reactive oxygen species in response to outer membrane perturbation. These lysine hydrochloride-β-lactam data support the hypothesis that lethal stressors can stimulate the accumulation of ROS. Genetic and biochemical work also revealed how an alteration in a membrane protease, FtsH, abolishes lysine stimulation of β-lactam lethality. Overall, the work presents a method for antimicrobial enhancement that should be safe, easy to administer, and likely to apply to other nutrients, such as arginine.

An AIE-active bacterial inhibitor and photosensitizer for selective imaging, killing, and photodynamic inactivation of bacteria over mammalian cells.

Photodynamic therapy is becoming increasingly popular for combat of bacteria. In the clinical photodynamic combat of bacteria, one critical issue is to avoid the potential damage to the host since the reactive oxygen species produced by photosensitizers are also harmful to mammalian cells. In this work, we report an aggregation-induced-emission-active bacterial inhibitor and photosensitizer, OEO-TPE-MEM (OTM), for the imaging, killing, and light-enhanced inactivation of bacteria. OTM could efficiently bind to and kill Gram-positive bacteria, while its affinity to Gram-negative bacteria is lower, and a higher OTM concentration is required for killing Gram-negative bacteria. OTM is also an efficient photosensitizer and could efficiently sensitize the production of reactive oxygen species, which enhances its killing effect on both Gram-positive and Gram-negative bacteria. More interestingly, OTM is very biocompatible with normal mammalian cells both in the dark and under light irradiation. OTM in mice models with bacteria-infected wounds could promote the healing of infected wounds without affecting their organs and blood parameters, which makes it an excellent candidate for clinical applications.

A hydrogel dressing with tunable critical temperature and photothermal modulating melittin release for multiply antibacterial treatment

It is imperative to develop an antibiotic-free and long-term effective strategy for treating chronic wound infections due to the long-term utilization of antibiotics easily causing drug resistance. Herein, we fabricated a novel poly-N-isopropylacrylamide (PNIPAM)/polyacrylamide (PAM) coupling thermosensitive hydrogel integrating 1D lysozyme nanofiber doped with CuS nanoparticles (CuS/PP) and loading antibacterial peptide melittin (M) (CuS/PP-M) for combating chronic wound infection via photothermal modulating the release of melittin. For the CuS/PP-M hydrogel, the copolymerization of PNIPAM and PAM allows the lower critical solution temperature (LCST) higher than the body temperature, effectively hindering the spontaneous release of melittin when contacts the infected wound, while the integration of LNF/CuS nanofibers provides a stable photothermal treatment for triggering the release of melittin. As a result, the CuS/PP-M hydrogel exhibits synergistically enhanced effect on killing both Gram-positive and Gram-negative bacteria, which maintains more than 99 % bactericidal efficiency, even displays a long-term and multiply antibacterial performance by photothermal modulating melittin release. Moreover, the CuS/PP-M hydrogel presents both high antibacterial activity and excellent wound healing performance in the mouse wound model, thereby benefiting the chronic wound healing.

A H2 O2 -Supplied Supramolecular Material for Post-irradiated Infected Wound Treatment.

Photodynamic therapy (PDT) is a light triggered therapy by producing reactive oxygen species (ROS), but traditional PDT may suffer from the real-time illumination that reduces the compliance of treatment and cause phototoxicity. A supramolecular photoactive G-quartet based material is reported, which is self-assembled from guanosine (G) and 4-formylphenylboronic acid/1,8-diaminooctane, with incorporation of riboflavin as a photocatalyst to the G4 nanowire, for post-irradiation photodynamic antibacterial therapy. The G4-materials, which exhibit hydrogel-like properties, provide a scaffold for loading riboflavin, and the reductant guanosine for the riboflavin for phototriggered production of the therapeutic H2 O2 . The photocatalytic activity shows great tolerance against room temperature storage and heating/cooling treatments. The riboflavin-loaded G4 hydrogels, after photo-irradiation, are capable of killing gram-positive bacteria (e.g., Staphylococcus aureus), gram-negative bacteria (e.g., Escherichia coli), and multidrug resistant bacteria (methicillin-resistant Staphylococcus aureus) with sterilization ratio over 99.999%. The post-irradiated hydrogels also exhibit great antibacterial activity in the infected wound of the rats, revealing the potential of this novel concept in the light therapy.

Tuning the Molecular Structure of Corroles to Enhance the Antibacterial Photosensitizing Activity.

The increase in the antibiotic resistance of bacteria is a serious threat to public health. Photodynamic inactivation (PDI) of micro-organisms is a reliable antimicrobial therapy to treat a broad spectrum of complex infections. The development of new photosensitizers with suitable properties is a key factor to consider in the optimization of this therapy. In this sense, four corroles were designed to study how the number of cationic centers can influence the efficacy of antibacterial photodynamic treatments. First, 5,10,15-Tris(pentafluorophenyl)corrole (Co) and 5,15-bis(pentafluorophenyl)-10-(4-(trifluoromethyl)phenyl)corrole (Co-CF3) were synthesized, and then derivatized by nucleophilic aromatic substitution with 2-dimethylaminoethanol and 2-(dimethylamino)ethylamine, obtaining corroles Co-3NMe2 and Co-CF3-2NMe2, respectively. The straightforward synthetic strategy gave rise to macrocycles with different numbers of tertiary amines that can acquire positive charges in an aqueous medium by protonation at physiological pH. Spectroscopic and photodynamic studies demonstrated that their properties as chromophores and photosensitizers were unaffected, regardless of the substituent groups on the periphery. All tetrapyrrolic macrocycles were able to produce reactive oxygen species (ROS) by both photodynamic mechanisms. Uptake experiments, the level of ROS produced in vitro, and PDI treatments mediated by these compounds were assessed against clinical strains: methicillin-resistant Staphylococcus aureus and Klebsiella pneumoniae. In vitro experiments indicated that the peripheral substitution significantly affected the uptake of the photosensitizers by microbes and, consequently, the photoinactivation performance. Co-3NMe2 was the most effective in killing both Gram-positive and Gram-negative bacteria (inactivation > 99.99%). This work lays the foundations for the development of new corrole derivatives having pH-activable cationic groups and with plausible applications as effective broad-spectrum antimicrobial photosensitizers.

Ultra-Short Cyclized β-Boomerang Peptides: Structures, Interactions with Lipopolysaccharide, Antibiotic Potentiator and Wound Healing.

Many antibiotics are ineffective in killing Gram-negative bacteria due to the permeability barrier of the outer-membrane LPS. Infections caused by multi-drug-resistant Gram-negative pathogens require new antibiotics, which are often difficult to develop. Antibiotic potentiators disrupt outer-membrane LPS and can assist the entry of large-scaffold antibiotics to the bacterial targets. In this work, we designed a backbone-cyclized ultra-short, six-amino-acid-long (WKRKRY) peptide, termed cWY6 from LPS binding motif of β-boomerang bactericidal peptides. The cWY6 peptide does not exhibit any antimicrobial activity; however, it is able to permeabilize the LPS outer membrane. Our results demonstrate the antibiotic potentiator activity in the designed cWY6 peptide for several conventional antibiotics (vancomycin, rifampicin, erythromycin, novobiocin and azithromycin). Remarkably, the short cWY6 peptide exhibits wound-healing activity in in vitro assays. NMR, computational docking and biophysical studies describe the atomic-resolution structure of the peptide in complex with LPS and mode of action in disrupting the outer membrane. The dual activities of cWY6 peptide hold high promise for further translation to therapeutics.

Antimicrobial peptide functionalized gold nanorods combining near-infrared photothermal therapy for effective wound healing

Photothermal therapy using laser activated gold nanorods (AuNRs) is a strategy for treatment of bacterial infections. Nevertheless, it also exerts cytotoxicity against human cells which leads to adverse effects in healthy human tissues and limits the applicable dose. Functionalization of AuNRs with a selective antimicrobial peptide (AMP) with higher selectivity for bacteria over human cells is a promising strategy for increasing the selectivity of the AuNRs for bacteria, hence increasing their cellular uptake by the bacteria in order to achieve stronger antimicrobial effects with lower doses of AuNRs without damaging the human cells. In this study, the surface of AuNRs was functionalized with a short AMP named C-At5 and the efficiency of the peptide functionalized AuNRs in killing gram-positive and gram-negative bacteria was evaluated in vitro as well as their potential for facilitating wound healing in a mouse model of wound infection with and without application of laser. The peptide-conjugated AuNRs exhibited higher antibacterial activity in vitro compared to the plain AuNRs both in the presence and absence of laser irradiation. Furthermore, AuNR@C-At5 had very low toxicity against human skin fibroblasts and human red blood cells indicating their higher biocompatibility compared to the plain AuNRs. Treatment of wounded mice with AuNR@C-At5 accelerated the wound healing process which was further enhanced by applying laser. The system developed in this study has great potential for customization for specific antimicrobial or antifungal therapy via conjugation of different types of AMPs with higher selectivity and can therefore serve as a guide for any future attempts in this regard.

Application of bottom ash from cattle manure combustion for removing fluoride and inactivating pathogenic bacteria in wastewater

This study addressed the utilization of bottom ash derived from the combustion of cattle manure (BA-CM) for removing fluoride from industrial wastewater and killing gram-negative (E. coli O157:H7 and S. typhimurium) and gram-positive pathogenic bacteria (L. monocytogenes), and it will ensure both the disposal of solid waste and the purification of water. BA-CM had a pore size corresponding to mesopores (2–50 nm) and a fractal dimension (D) of 2.88. The main elements constituting the BA-CM were calcium (Ca) in the form of Ca5(PO4)3(OH) and CaCO3. The Ca released from BA-CM was helpful for removing fluoride via the formation of CaF2. The fluoride adsorption by BA-CM approached equilibrium after 6 h. The fluoride equilibrium adsorption on to BA-CM was well fitted to the Langmuir model and was calculated to have a maximum adsorption capacity of 112.07 mg/g. At pH 3, the adsorption amount of fluoride was 76.33 mg/g, and as the pH increased to 7, fluoride adsorption decreased to 50.74 mg/g. In the pH range of 7–11, the amount of fluoride adsorbed did not decrease and was maintained (50.53 ± 0.22 mg/g). More than 97% fluoride removal could be achieved using 13.33 g/L of BA-CM. BA-CM treatment effectively inactivated pathogens in the contaminated water. The BA-CM treatment for 4 min achieved 3.77 log CFU/mL and 6.56 log CFU/mL reductions in E. coli O157:H7 and S. typhimurium, respectively. L. monocytogenes exhibited higher resistance to BA-CM than the other pathogens tested, and 30 min was required to achieve a reduction of 6.33 log CFU/mL. BA-CM, obtained from the combustion of cattle manure for energy production, can be used as a value-added material for removing fluoride and disinfecting water contaminated with pathogenic bacteria.

Optimizing the electronic structure of BiOBr via constructing oxygen-rich vacancies for highly efficient NIR light-driven antibacterial activity

Two-dimensional (2D) layered nanomaterials showed great promise in the photocatalysis due to their unique physical properties. Defect engineering enables significant optimization of the electronic structure of 2D nanomaterials to further enhance their photocatalytic activity. Herein, we designed two oxygen-rich vacancies BiOBr (BBR) and oxygen-poor vacancies BiOBr (BBP) to investigate their photocatalytic activities. The results demonstrated that BBR exhibited much higher activity than BBP in killing Gram-negative (Escherichia coli, E. coli) and Gram-positive bacteria (Bacillus subtilis, B. subtilis) under 808 nm laser irradiation. The enhanced antibacterial activity can be attributed to optimized electronic structure of BBR, which leads to more intimate interactions with bacteria, stronger absorption capacity to near-infrared (NIR) light, and longer photocarriers lifetime. Moreover, density functional theory (DFT) calculations demonstrated that BBR has a better adsorption of O2, which facilitates the generation of more reactive oxygen species (ROS) for superior activity. This work not only provides a facile approach for constructing oxygen-rich vacancies in BiOBr, but also but also offers new insights to the potential of 2D materials optimized by defect engineering for efficient NIR light-driven antibacterial activity.

Facile and Novel Synthesis of Spiky Gold Nanoparticles as an Efficient Antimicrobial Agent against Pseudomonas Aeruginosa.

The aim of the study is to develop advanced antibacterial agents as nanoparticles instead of antibiotics due to the emergence of antimicrobial resistance. Pseudomonas aeruginosa is capable of causing many diseases, including serious bacterial pneumonia. There is a need for an efficient antibacterial agent to kill these pathogens. The objective of the study is the synthesis of advanced antibacterial agents as nanoparticles for biomedical applications that can play a vital role to kill Gram-negative bacteria (Pseudomonas aeruginosa). A novel fabrication growth of hydrophilic spiky gold nanoparticles (SGNPs) via reduction method is reported. Surface plasmon resonance peak of the synthesized SGNPs was tuned under near infrared range. The SGNPs have anisotropic and spiky morphology with 68 nm size and -58 mV surface charge and are pure, having adsorption of the organic material. Pseudomonas aeruginosa treated with synthesized SGNPs showed 60% bacterial death at the concentration of 100 μM. This work consists of novel synthesis of SGNPs via safe and simple reduction method. The synthesized SGNPs exhibit strong antibacterial activity against the Gram negative bacteria Pseudomonas aeruginosa measured using microplate assay test. The result showed that these SGNPs are ideal for biomedical applications.

In-biofilm generation of nitric oxide using a magnetically-targetable cascade-reaction container for eradication of infectious biofilms

Cascade-reaction chemistry can generate reactive-oxygen-species that can be used for the eradication of infectious biofilms. However, suitable and sufficient oxygen sources are not always available near an infection site, while the reactive-oxygen-species generated are short-lived. Therefore, we developed a magnetic cascade-reaction container composed of mesoporous Fe3O4@SiO2 nanoparticles containing glucose-oxidase and l-arginine for generation of reactive-oxygen-species. Glucose-oxidase was conjugated with APTES facilitating coupling to Fe3O4@SiO2 nanoparticles and generation of H2O2 from glucose. l-arginine was loaded into the nanoparticles to generate NO from the H2O2 generated. Using an externally-applied magnetic field, cascade-reaction containers could be homogeneously distributed across the depth of an infectious biofilm. Cascade-reaction containers with coupled glucose-oxidase were effective in killing planktonic, Gram-positive and Gram-negative bacteria. Additional efficacy of the l-arginine based second cascade-reaction was only observed when H2O2 as well as NO were generated in-biofilm. In vivo accumulation of cascade-reaction containers inside abdominal Staphylococcus aureus biofilms upon magnetic targeting was observed real-time in living mice through an implanted, intra-vital window. Moreover, vancomycin-resistant, abdominal S. aureus biofilms could be eradicated consuming solely endogenous glucose, without any glucose addition. Herewith, a new, non-antibiotic-based infection-control strategy has been provided, constituting a welcome addendum to the shrinking clinical armamentarium to control antibiotic-resistant bacterial infections.

Development of a BLI assay-based method for detecting LptA/LptC interaction

In Gram-negative bacteria, lipopolysaccharide transport (Lpt) protein LptA and LptC form a complex to transport LPS from the inner membrane (IM) to the outer membrane (OM). Blocking the interaction between LptA and LptC will lead to the defect of OM and cell death. Therefore, Lpt protein interaction could be used as a target to screen new drugs for killing Gram-negative bacteria. Here we used biolayer interferometry (BLI) assay to detect the interaction between LptA and LptC, with the aim to develop a method for screening the LptA/LptC interaction blockers in vitro. Firstly, LptC and LptA with or without signal peptide (LptAfull or LptAno signal) were expressed in E. coli BL21(DE3). The purified proteins were then labeled with biotin and the super streptavidin (SSA) biosensor was blocked with diluent. The biotin labeled protein sample was mixed with the sensor, and then the binding of the protein with a series of diluted non biotinylated protein was detected. At the same time, non-biotinylated protein was used as a control. The binding of biotinylated protein to a small molecule IMB-881 and the blocking of interaction were also detected by the same method. In the blank control, the biosensor without biotinylated protein was used to detect the serially diluted samples. The signal response constant was calculated by using steady analysis. The results showed that biotinylated LptC had a good binding activity with LptAfull and LptAno signal with KD value 2.9e⁻⁷±7.9e⁻⁸ and 6.0e⁻⁷±2.8e⁻⁸, respectively; biotinylated LptAno signal had a good binding activity with LptC, with a KD value of 9.6e⁻⁷±7.2e⁻⁸. All binding curves showed obvious fast binding and fast dissociation morphology. The small molecule compound IMB-881 can bind to LptA to block the interaction between LptA and LptC, but has no binding activity with LptC. In summary, we developed a method for detecting the LptA/LptC interaction based on the BLI technology, and confirmed that this method can be used to evaluate the blocking activity of small molecule blockers, providing a new approach for the screening of LptA/LptC interaction blockers.

The Efficacy of Silver-Based Electrospun Antimicrobial Dressing in Accelerating the Regeneration of Partial Thickness Burn Wounds Using a Porcine Model.

(1) Background: Wounds with damages to the subcutaneous are difficult to regenerate because of the tissue damages and complications such as bacterial infection. (2) Methods: In this study, we created burn wounds on pigs and investigated the efficacy of three biomaterials: polycaprolactone-gelatin-silver membrane (PCLGelAg) and two commercial burn dressings, Aquacel® Ag and UrgoTulTM silver sulfadiazine. In vitro long-term antibacterial property and in vivo wound healing performance were investigated. Agar diffusion assays were employed to evaluate bacterial inhibition at different time intervals. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and time-kill assays were used to compare antibacterial strength among samples. Second-degree burn wounds in the pig model were designed to evaluate the efficiency of all dressings in supporting the wound healing process. (3) Results: The results showed that PCLGelAg membrane was the most effective in killing both Gram-positive and Gram-negative bacteria bacteria with the lowest MBC value. All three dressings (PCLGelAg, Aquacel, and UrgoTul) exhibited bactericidal effect during the first 24 h, supported wound healing as well as prevented infection and inflammation. (4) Conclusions: The results suggest that the PCLGelAg membrane is a practical solution for the treatment of severe burn injury and other infection-related skin complications.

Near-Infrared Light-Activated Phototherapy by Gold Nanoclusters for Dispersing Biofilms.

A bacterial biofilm is strongly associated with chronic infections and is difficult to be eradicated, posing serious threats to public health. Development of effective therapeutic strategies to prevent and control hospital-acquired infections via eradication of bacteria shielded by biofilms is challenging. Herein, we developed deoxyribonuclease (DNase)-functionalized gold nanoclusters (AuNCs) (DNase-AuNCs), which are capable of killing Gram-positive and Gram-negative bacteria, especially dispersing the surrounding biofilms. The DNase can break down the extracellular polymeric substance matrix to expose the defenseless bacteria to photothermal therapy (PTT) and photodynamic therapy (PDT) by DNase-AuNCs under 808 nm laser irradiation. The combination of enzymolysis, PDT, and PTT can effectively remove biofilms with a dispersion rate of up to 80% and kill ∼90% of the shielded bacteria. DNase-AuNCs exhibit an outstanding therapeutic effect in treating bacterial biofilm-coated orthodontic devices (Invisalign aligners), suggesting their potential applications in medical devices.

Combination of guanidinium and quaternary ammonium polymers with distinctive antimicrobial mechanisms achieving a synergistic antimicrobial effect.

The increasing emergence and spread of antimicrobial resistance are urgent and important global challenges today. The clinical pipeline is lacking in innovative drugs that avoid the development of drug resistance. Macromolecular antimicrobials kill bacteria and fungi through physical disruptions to the cell membrane, which is difficult for microbes to overcome. Recently, we reported antimicrobial polycarbonates that kill microbes via two different mechanisms. Polycarbonates functionalized with quaternary ammonium disrupted the lipid bilayer membrane of the microbes, while polycarbonates functionalized with guanidinium translocated the membrane and precipitated cytosolic components. We hypothesized that the combination of these two distinct mechanisms would result in a more than additive increase in antimicrobial efficacy. Block and random copolymers containing both cationic groups had similar minimum inhibitory concentrations (MICs) as the guanidinium homopolymer on 5 representatives of the ESKAPE pathogens. Interestingly, the random copolymer killed P. aeruginosa and A. baumannii more rapidly than the block copolymer and the guanidinium homopolymer with the same number of guanidinium groups. Like quaternary ammonium homopolymer, the copolymers killed the bacteria via a membrane-disruptive mechanism. Then, we simply mixed quaternary ammonium homopolymer and guanidinium homopolymer, and studied antimicrobial activity of the combination at various concentrations. Checkerboard assay results showed that the combination of the polymers, in general, achieved a synergistic or additive effect in inhibiting the growth of bacteria. At concentrations where it exibited a synergistic or additive effect in inhibiting bacterial growth, the combination killed the bacteria effectively (99%-99.9% killing efficiency) although the individual polymers at these concentrations did not exert bactericidal activity. Therefore, it is essential to have the two functional groups on separate molecules to provide synergism. This study provides a basic understanding of polymer design with different cationic groups.

Lysozyme (Lys), Tannic Acid (TA), and Graphene Oxide (GO) Thin Coating for Antibacterial and Enhanced Osteogenesis.

Dental implants have great potential in the global market, around $3.7 billion in 2015, which will increase to $7 billion in 2023 with an annual increase rate of 8.2%. Incorporating antibacterial and osteogenic agents into implants is helpful to make the dental implants successful, which can be endowed by coatings. In recent years, graphene oxide (GO) and its composite materials have shown advances in the biomedical field. Lysozyme (Lys) and tannic acid (TA) are naturally derived, with promising antibacterial and osteogenic properties as well. In the present study, the strong antibacterial and enhanced osteogenic multilayer coating is fabricated using the facile and controllable layer by layer (LBL) technique to integrate GO, Lys, and TA. The thickness of coating exhibited a continuous growth with the deposited process as proved from UV-vis and ellipsometry data, and the physical properties of the coating, such as wettability, roughness, and stiffness are well characterized. The coatings exhibited the synergic effect on the killing bacteria, both Gram-negative bacteria and Gram-positive bacteria represented by E. coli and S. aureus, respectively, and enhancing osteogenesis of dental pulp stem cells (hDPSCs), showing the potential application on coatings of dental implants. Thus, the strategy applied here will inspire the design and development of dual functional surfaces for the success of implanted dental surface in future.