Dual Function Injectable Hydrogel for Controlled Release of Antibiotic and Local Antibacterial Therapy

We present vancomycin-loaded dual-function injectable hydrogel that delivers antibiotic locally suitable for treatment of infections in avascular or necrotic tissues. The syringe-deliverable gels were developed using polydextran aldehyde and an inherently antibacterial polymer <i>N</i>-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride along with vancomycin. The antibiotic was primarily encapsulated via reversible imine bonds formed between vancomycin and polydextran aldehyde in the hydrogel which allowed sustained release of vancomycin over an extended period of time in a pH-dependent manner. Being inherently antibacterial, the gels displayed excellent efficacy against bacteria due to dual mode of action (killing bacteria upon contact as well as by releasing antibiotics into surroundings). Upon subcutaneous implantation, the gel was shown to kill methicillin-resistant Staphylococcus aureus (>99.999%) when bacteria were introduced directly into the gel as well as at distal site from the gel in a mice model. These materials thus represent as novel noninvasive drug-delivery device suitable for local antibiotic therapy

Biocompatible Injectable Hydrogel with Potent Wound Healing and Antibacterial Properties

Two component injectable hydrogels that cross-link in situ have been used as noninvasive wound-filling devices, i.e., sealants. These materials carry a variety of functions at the wound sites, such as sealing leaks, ceasing unwanted bleeding, binding tissues together, and assisting in wound healing processes. However, commonly used sealants typically lack antibacterial properties. Since bacterial infection at the wound site is very common, bioadhesive materials with intrinsic antibacterial properties are urgently required. Herein, we report a biocompatible injectable hydrogel with inherent bioadhesive, antibacterial, and hemostatic capabilities suitable for wound sealing applications. The hydrogels were developed in situ from an antibacterial polymer, <i>N</i>-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC), and a bioadhesive polymer, polydextran aldehyde. The gels were shown to be active against both Gram-positive and Gram-negative bacteria, including drug-resistant ones such as methicillin-resistant <i>Staphylococcus aureus</i> (MRSA), vancomycin-resistant <i>Enterococcus faecium</i> (VRE), and β-lactam-resistant <i>Klebsiela pneumoniae</i>. Mechanistic studies revealed that the gels killed bacteria upon contact by disrupting the membrane integrity of the pathogen. Importantly, the gels were shown to be efficacious in preventing sepsis in a cecum ligation and puncture (CLP) model in mice. While only 12.5% of animals survived in the case of mice with punctured cecam but with no gel on the punctured area (control), 62.5% mice survived when the adhesive gel was applied to the punctured area. Furthermore, the gels were also shown to be effective in facilitating wound healing in rats and ceasing bleeding from a damaged liver in mice. Notably, the gel showed negligible toxicity toward human red blood cells (only 2–3% hemolysis) and no inflammation to the surrounding tissue upon subcutaneous implantation in mice, thus proving it as a safe and effective antibacterial sealant

Vancomycin Analogue Restores Meropenem Activity against NDM‑1 Gram-Negative Pathogens

New Delhi metallo-β-lactamase-1 (NDM-1) is the major contributor to the emergence of carbapenem resistance in Gram-negative pathogens (GNPs) and has caused many clinically available β-lactam antibiotics to become obsolete. A clinically approved inhibitor of metallo-β-lactamase (MBL) that could restore the activity of carbapenems against resistant GNPs has not yet been found, making NDM-1 a serious threat to human health. Here, we have rationally developed an inhibitor for the NDM-1 enzyme, which has the ability to penetrate the outer membrane of GNPs and inactivate the enzyme by depleting the metal ion (Zn²⁺) from the active site. The inhibitor reinstated the activity of meropenem against NDM-1 producing clinical isolates of GNPs like <i>Klebsiella pneumoniae</i> and <i>Escherichia coli</i>. Further, the inhibitor efficiently restored meropenem activity against NDM-1 producing <i>K. pneumoniae</i> in a murine sepsis infection model. These findings demonstrate that a combination of the present inhibitor and meropenem has high potential to be translated clinically to combat carbapenem-resistant GNPs

Membrane-Active Macromolecules Resensitize NDM-1 Gram-Negative Clinical Isolates to Tetracycline Antibiotics

<div><p>Gram-negative ‘superbugs’ such as New Delhi metallo-beta-lactamase-1 (<i>bla</i>_NDM-1) producing pathogens have become world’s major public health threats. Development of molecular strategies that can rehabilitate the ‘old antibiotics’ and halt the antibiotic resistance is a promising approach to target them. We report membrane-active macromolecules (MAMs) that restore the antibacterial efficacy (enhancement by >80-1250 fold) of tetracycline antibiotics towards <i>bla</i>_NDM-1<i>Klebsiella pneumonia</i> and <i>bla</i>_NDM-1<i>Escherichia coli</i> clinical isolates. Organismic studies showed that bacteria had an increased and faster uptake of tetracycline in the presence of MAMs which is attributed to the mechanism of re-sensitization. Moreover, bacteria did not develop resistance to MAMs and MAMs stalled the development of bacterial resistance to tetracycline. MAMs displayed membrane-active properties such as dissipation of membrane potential and membrane-permeabilization that enabled higher uptake of tetracycline in bacteria. <i>In-vivo</i> toxicity studies displayed good safety profiles and preliminary <i>in-vivo</i> antibacterial efficacy studies showed that mice treated with MAMs in combination with antibiotics had significantly decreased bacterial burden compared to the untreated mice. This report of re-instating the efficacy of the antibiotics towards <i>bla</i>_NDM-1 pathogens using membrane-active molecules advocates their potential for synergistic co-delivery of antibiotics to combat Gram-negative superbugs.</p></div

Antibacterial activity of NCK-10 at different physiological conditions.

<p>Antibacterial activity of NCK-10 at different physiological conditions.</p

Ability of NCK-10 to disrupt methicillin resistant <i>S</i>. <i>aureus</i> biofilms.

<p>(A) Reduction in viable bacterial count with respect to control at different concentrations of NCK-10. (B) Reduction in biofilm mass by crystal violet staining (Concentration of NCK-10 was 10×MIC). (C) Confocal of image of untreated biofilm and after treatment with NCK-10 (Concentration of NCK-10 was 10×MIC).</p

Skin histopathology studies.

<p>(A) Untreated (B) Treated with Fusidic acid and (C) Treated with NCK-10.</p

Synergy, resistance development and <i>in-vivo</i> antibacterial efficacy of MAMs and tetracycline antibiotics against <i>bla</i>_NDM-1<i>E</i>. <i>coli</i> (R3336).

<p>(A) The combination of MAM1 and minocycline (50 μg mL^-1 + 6.3 μg mL^-1) showed synergistic bactericidal activity whereas MAM1 (50 μg mL^-1) alone and minocycline alone (6.3 μg mL^-1) were devoid of antibacterial activity (star represents < 50 CFU mL^-1, the detection limit of the experiment). (B) Bacteria developed resistance to minocycline alone with increase in MIC up to 400 μg mL^-1 whereas it did not develop resistance to minocycline (6.2 μg mL^-1) in presence of MAM1 (50 μg mL^-1) up to 30 days. Bacteria did not readily develop resistance to MAM1 whereas it developed resistance to colistin with an increase in MIC up to 1000 μg mL^-1. (C) <i>In-vivo</i> antibacterial efficacy of MAM1 and doxycycline in mice models. The bacterial burden in the thighs of the mice (4 mice in each group) were determined and expressed as mean ± S.E.M (standard error of mean). P value was calculated using the unpaired Student’s <i>t</i> test (2 tailed 2 samples assuming equal variances) and a value P < 0.05 was considered significant. *P = 0.03 between the saline treated and combination treated samples (Inset shows the experimental design).</p

Structures of the compounds used in the study.

<p>Structures of the compounds used in the study.</p

Kinetics of killing of <i>S</i>. <i>aureus</i> persister cells by NCK-10 at 5 × MIC.

<p>(*) indicate that no colony was observed.</p