Sudeep Goswami

Membrane-Directed High Bactericidal Activity of (Gold Nanoparticle)–Polythiophene Composite for Niche Applications Against Pathogenic Bacteria

The use of nanoscale materials as bactericidal agents represents a novel paradigm in the development of therapeutics against drug-resistant pathogenic bacteria. In this paper the antimicrobial activity of a water soluble (gold nanoparticle)-polythiophene (AuNP-PTh) composite against common bacterial pathogens is reported. The nanocomposite is broad-spectrum in its bactericidal activity and exhibits a membrane-directed mode of action on target pathogens. The therapeutic potency of AuNP-PTh is demonstrated by experiments which reveal that the nanocomposite can breach the outer membrane defense barrier of Gram-negative pathogens for subsequent killing by a hydrophobic antibiotic, inhibit the growth of model gastrointestinal pathogens in simulated gastric fluid, and significantly eradicate bacterial biofilms. The high bacterial selectivity and lack of cytotoxicity on human cells augers well for future therapeutic application of the nanocomposite against clinically relevant pathogenic bacteria.

Biocompatible nanocarrier fortified with a dipyridinium-based amphiphile for eradication of biofilm.

Annihilation of bacterial biofilms is challenging owing to their formidable resistance to therapeutic antibiotics and thus there is a constant demand for development of potent antibiofilm agents that can abolish established biofilms. In the present study, the activity of a dipyridinium-based cationic amphiphile (compound 1) against established bacterial biofilms and the subsequent development of a compound 1-loaded nanocarrier for potential antibiofilm therapy are highlighted. Solution-based assays and microscopic analysis revealed the antagonistic effect of compound 1 on biofilms formed by Staphylococcus aureus MTCC 96 and Pseudomonas aeruginosa MTCC 2488. In combination studies, compound 1 could efficiently potentiate the action of tobramycin and gentamicin on P. aeruginosa and S. aureus biofilm, respectively. A human serum albumin (HSA)-based nanocarrier loaded with compound 1 was generated, which exhibited sustained release of compound 1 at physiological pH. The compound 1-loaded HSA nanocarrier (C1-HNC) displayed the signature membrane-directed activity of the amphiphile on target bacteria, efficiently eliminated established bacterial biofilms, and was observed to be nontoxic to a model human cell line. Interestingly, compound 1 as well as the amphiphile-loaded HSA nanocarrier could eradicate established S. aureus biofilm from the surface of a Foleys urinary catheter. On the basis of its biocompatibility and high antibiofilm activity, it is conceived that the amphiphile-loaded nanocarrier may hold potential in antibiofilm therapy.

Tuning the bactericidal repertoire and potency of quinoline-based amphiphiles for enhanced killing of pathogenic bacteria

The overwhelming challenge posed by drug-resistant pathogenic bacteria underscores the need for potent bactericidal agents, which exhibit broad-spectrum activity and a mode of action that does not favor development of resistance. In the present study we report the synthesis and bactericidal activity of structurally diverse quinoline-based amphiphiles, having a fluorescent head group and varying hydrophobic chain length. A structure-guided bactericidal efficacy and broad-spectrum activity of the amphiphiles was apparent in screening experiments against a panel of common pathogenic bacteria. Structure–function studies by fluorescence-based assays revealed that the charge and hydrophobic chain length of amphiphiles were key structural determinants that radically boosted the bactericidal activity. The most potent amphiphile N-methyl 8-dodecoxy quinolinium iodide (compound 6) exhibited a dose-dependent bactericidal activity on target pathogens and could even inhibit the growth of a presumptive methicillin-resistant S. aureus (MRSA) strain. Fluorescence-based mechanistic studies and transmission electron microscope (TEM) analysis indicated that the initial binding of compound 6 to bacteria probably involved electrostatic interaction, whereas the hydrophobic chain of the amphiphile promoted membrane insertion, which culminated in large scale membrane disruption and loss in cell viability. Although the bactericidal activity of compound 6 was independent of bacterial transmembrane potential, interaction of the amphiphile with pathogenic bacteria resulted in rapid dissipation of membrane potential. Interestingly, compound 6 displayed high antimicrobial selectivity and did not affect the viability of human HT-29 cells. It is envisaged that the therapeutic regime of the bactericidal scaffold of compound 6 can be further expanded by rational structural design for generating potent bactericidal agents.

Synthetic amphiphiles as therapeutic antibacterials: lessons on bactericidal efficacy and cytotoxicity and potential application as an adjuvant in antimicrobial chemotherapy

In this paper, we present a critical assessment of the therapeutic potential of low molecular weight pyridine-based synthetic amphiphiles based on structure-guided bactericidal activity and a rational evaluation of their cytotoxic potential. Fluorescence-based structure-function studies revealed that the amphiphiles were membrane-acting and displayed a hierarchical pattern of bactericidal activity, which could be correlated with their charge density and hydrophobicity. The membrane-targeting activity of the most potent cationic amphiphile (compound 6) was vindicated as it induced extensive membrane-disruption and dissipation of the transmembrane potential (ΔΨ) in pathogenic bacteria. At concentrations equivalent to the minimum inhibitory concentration (MIC) against the Gram-positive pathogen S. aureus MTCC 96, none of the amphiphiles exerted any cytotoxic effect on model human cell lines (HeLa, MCF-7 and HT-29). However, at elevated concentrations, a distinct gradation in the cytotoxic effect was manifested, which is probably accounted by the charge density and conformational flexibility of the amphiphiles. A viable therapeutic application of compound 6 is demonstrated in combinatorial assays, wherein the proclivity of the amphiphile to disrupt bacterial membranes at very low concentration is exploited to enhance the uptake and bactericidal efficacy of erythromycin against Gram-negative pathogenic bacteria.

A zinc complex of a neutral pyridine-based amphiphile: a highly efficient and potentially therapeutic bactericidal material

The alarming rise in antibiotic-resistant pathogenic bacteria demands a prudent approach in the generation of therapeutic antibacterials. The present study illustrates the development of a potent amphiphilic bactericidal material tailored to leverage interactions with metal-reactive groups (MRGs) present in the bacterial cell surface envelope. Complexation of Zn(ii) with a neutral pyridine-based synthetic amphiphile (C1) generated the cationic C1-Zn, which exhibited manyfold higher membrane-directed bactericidal activity compared to the neutral C1, or the cationic amphiphile bearing two pyridinium head groups (C2). The relevance of MRGs in C1-Zn-bacteria interactions was validated by amphiphile-bacteria binding studies and metal protection assays performed with Mg(ii). C1-Zn retained its bactericidal activity even in simulated gastric fluid (SGF) and the enhanced membrane-directed bactericidal activity of C1-Zn could be garnered in adjuvant applications to increase the efficacy of the therapeutic antibiotic erythromycin. Given the relevance of Zn(ii) in S. aureus biofilm formation, the antibiofilm potential of the amphiphile C1 realized through Zn(ii) complexation could be demonstrated. The lack of resistance in target bacteria coupled with a favorable therapeutic index (IC50/MIC) and non-toxic nature hold significant implications for C1-Zn as a potential antibacterial therapeutic material.

Amphiphile-mediated enhanced antibiotic efficacy and development of a payload nanocarrier for effective killing of pathogenic bacteria

Synthetic amphiphiles have emerged as potent bactericidal scaffolds owing to their high propensity to interact with bacterial cells and a membrane-directed mode of action, which is likely to overcome resistance development in pathogenic bacteria. In this study, we highlighted a membrane-acting quinolinium-based cationic amphiphile (compound 1) as an adjuvant for antibiotic-mediated eradication of pathogenic bacteria and demonstrated the generation of an amphiphile-loaded nanocarrier for potential antibacterial therapy. Treatment of Gram-negative pathogenic bacteria E. coli MTCC 433 and P. aeruginosa MTCC 2488 with 1 resulted in significant augmentation of the activity of erythromycin and a decrease in the minimum inhibitory concentration of the antibiotic. Interestingly, 1 promoted large-scale eradication of P. aeruginosa MTCC 2488 biofilm and could also enhance the anti-biofilm activity of tobramycin in combination. For potential therapeutic applications, a 1-loaded bovine serum albumin-based nanocarrier was developed, which exhibited sustained release of 1 both in physiological and acidic pH and the released amphiphile displayed antibacterial as well as anti-biofilm activities. Interestingly, the nanocarrier also displayed the signature membrane-directed activity of 1 against tested pathogenic bacteria. The high bactericidal and anti-biofilm activities in conjunction with a lack of cytotoxic effect on HT-29 human cell lines enhance the merit of the amphiphile-loaded nanocarrier as a potentially therapeutic antibacterial against clinically relevant drug-resistant pathogenic bacteria.