Membrane Active Vancomycin Analogues: A Strategy to Combat Bacterial Resistance

The alarming growth of antibiotic resistant superbugs such as vancomycin-resistant Enterococci and Staphylococci has become a major global health hazard. To address this issue, we report the development of lipophilic cationic vancomycin analogues possessing excellent antibacterial activity against several drug-resistant strains. Compared to vancomycin, efficacy greater than 1000-fold was demonstrated against vancomycin-resistant Enterococci (VRE). Significantly, unlike vancomycin, these compounds were shown to be bactericidal at low concentrations and did not induce bacterial resistance. An optimized compound in the series, compared to vancomycin, showed higher activity in methicillin-resistant Staphylococcus aureus (MRSA) infected mouse model and exhibited superior antibacterial activity in whole blood with no observed toxicity. The remarkable activity of these compounds is attributed to the incorporation of a new membrane disruption mechanism into vancomycin and opens up a great opportunity for the development of novel antibiotics

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

Structures of the compounds used in the study.

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

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

Small Molecular Antibacterial Peptoid Mimics: The Simpler the Better!

The emergence of multidrug resistant bacteria compounded by the depleting arsenal of antibiotics has accelerated efforts toward development of antibiotics with novel mechanisms of action. In this report, we present a series of small molecular antibacterial peptoid mimics which exhibit high in vitro potency against a variety of Gram-positive and Gram-negative bacteria, including drug-resistant species such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. The highlight of these compounds is their superior activity against the major nosocomial pathogen Pseudomonas aeruginosa. Nontoxic toward mammalian cells, these rapidly bactericidal compounds primarily act by permeabilization and depolarization of bacterial membrane. Synthetically simple and selectively antibacterial, these compounds can be developed into a newer class of therapeutic agents against multidrug resistant bacterial species

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

Aryl-alkyl-lysines: Membrane-Active Small Molecules Active against Murine Model of Burn Infection

Infections caused by drug-resistant Gram-negative pathogens continue to be significant contributors to human morbidity. The recent advent of New Delhi metallo-β-lactamase-1 (<i>bla</i>NDM-1) producing pathogens, against which few drugs remain active, has aggravated the problem even further. This paper shows that aryl-alkyl-lysines, membrane-active small molecules, are effective in treating infections caused by Gram-negative pathogens. One of the compounds of the study was effective in killing planktonic cells as well as dispersing biofilms of Gram-negative pathogens. The compound was extremely effective in disrupting preformed biofilms and did not select resistant bacteria in multiple passages. The compound retained activity in different physiological conditions and did not induce any toxic effect in female Balb/c mice until concentrations of 17.5 mg/kg. In a murine model of Acinetobacter baumannii burn infection, the compound was able to bring the bacterial burden down significantly upon topical application for 7 days

(A) Structures of the membrane active molecules (MAMs) and (B) Schematic representation of agarose gel (2%) showing the 475 bp amplified product by conventional polymerase chain reaction.

<p>Lane 1, 100 bp DNA ladder; Lane 2, positive control- NDM-1 producing <i>K</i>. <i>pneumoniae</i> (ATCC-BAA-2146); Lane 3, negative control- <i>E</i>. <i>coli</i> (ATCC-25922); Lane 4, <i>E</i>. <i>coli</i> R3336 and Lane 5, <i>K</i>. <i>pneumoniae</i> R3934 confirm the <i>bla</i>_NDM-1 gene; Lane 6, multi-drug resistant (MDR) <i>K</i>. <i>pneumoniae</i> R3421 which was negative for <i>bla</i>_NDM-1 gene.</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