Broad-spectrum derivatives of polymyxin B and colistin

An experimental study to evaluate the effect of polymixin E (Colistin) alone or in combination with gentamicin in McCarey-Kaufman corneal preservation medium on various drug resistant bacterial and fungal isolates

Purpose

To assess the efficacy of the addition of polymyxin E (colistin) in the McCarey-Kaufman (MK) corneal storage solution against multi-drug resistant strains of Enterobacteriaceae, Staphylococcus aureus, and Candida spp.

Methods

A standard micro broth dilution test and a checkerboard assay were performed for five multi-drug resistant (MDR) clinical strains of P. aeruginosa and five clinical strains of methicillin-resistant S. aureus (MRSA) and C. albicans against colistin and gentamicin alone and in combination. The minimum inhibitory concentration (MIC) and the fractional inhibitory concentration index (FICI) were calculated to assess the efficacy of each combination.

Results

The MIC of colistin was in the range of 1-2 μg/mL for P. aeruginosa, whereas it was 256-1024 μg/mL against S. aureus. In comparison, the MIC of gentamicin was found to be 0.5-512 μg/mL and 0.5-8 μg/mL against P. aeruginosa and S. aureus, respectively. All five isolates of C. albicans did not exhibit any susceptibility to either colistin or gentamicin even at a concentration of ≥ 512 μg/mL each. The checkerboard assay was performed to evaluate the nature of the interaction of the combination of colistin and gentamicin. Based on the FICI, it was observed that the colistin and gentamicin combination has a maximum synergistic effect (FIC <0.5) in 80% (4/5) for S. aureus isolates, whereas the maximum additive effect (FIC >0.5-4) was 100% (5/5) for P. aeruginosa and the minimum additive effect was 20% (1/5) for S. aureus isolates. Antagonism (FIC ≥ 4) was not observed in any combination between the strains used in the study. Both colistin and gentamicin alone or in combination were, however, ineffective against Candida spp.

Conclusion

The addition of colistin has an inhibitory effect on bacterial contamination that could be possibly caused by MDR strains and could potentially be considered as an additional additive in corneal storage media.

Mycobacterial Membranes as Actionable Targets for Lipid-Centric Therapy in Tuberculosis

Infectious diseases remain significant health concerns worldwide, and resistance is particularly common in patients with tuberculosis caused by Mycobacterium tuberculosis. The development of anti-infectives with novel modes of action may help overcome resistance. In this regard, membrane-active agents, which modulate membrane components essential for the survival of pathogens, present attractive antimicrobial agents. Key advantages of membrane-active compounds include their ability to target slow-growing or dormant bacteria and their favorable pharmacokinetics. Here, we comprehensively review recent advances in the development of membrane-active chemotypes that target mycobacterial membranes and discuss clinically relevant membrane-active antibacterial agents that have shown promise in counteracting bacterial infections. We discuss the relationship between the membrane properties and the synthetic requirements within the chemical scaffold, as well as the limitations of current membrane-active chemotypes. This review will lay the chemical groundwork for the development of membrane-active antituberculosis agents and will foster the discovery of more effective antitubercular agents.

Total and Semisyntheses of Polymyxin Analogues with 2-Thr or 10-Thr Modifications to Decipher the Structure-Activity Relationship and Improve the Antibacterial Activity

Herein, we report the total and semisyntheses of a series of polymyxin analogues with 2-Thr and 10-Thr modifications to reveal the structure-activity relationship (SAR), which has not been fully elucidated previously. We employed two total-synthetic strategies to facilitate the diversified replacements on 2-Thr or 10-Thr, respectively. Moreover, semisynthetic approaches were utilized to achieve selective esterification of 2-Thr or dual esterification of both 2- and 10-Thr. Based on the results of in vitro antibacterial assays, SAR analysis implicated that the replacement of 2-/10-Thr with amino acids carrying hydrophobic side chains can maintain the activity against Pseudomonas aeruginosa but had varied effects on other tested Gram-negative bacteria. The aminoacetyl esterification on 2-/10-Thr achieved excellent antibacterial activity, and the compound 76 exhibited 2-8-fold higher activity against different strains and lower toxicity toward the HK-2 cell line. This work explored the SAR of polymyxin 2-/10-Thr and provided a promising strategy for the development of novel polymyxin derivatives.

Lysine Analogue of Polymyxin B as a Significant Opportunity for Photodynamic Antimicrobial Chemotherapy

In order to highlight the potential of photodynamic antimicrobial chemotherapy in case of infections by antibiotic resistant-strains, a new antimicrobial peptide conjugate has been synthesized, consisting of a derivative of polymyxin B and a cationic porphyrin covalently attached together to a spacer. A polymyxin-derived moiety was subjected to a primary structural modification in the replacement of four diaminobutyrate residues with lysine ones. This modification was done in order to strongly reduce bactericidal activity, with the aim to eliminate the potential rise of polymyxin-resistant strains. Despite this modification, this new conjugate displayed a strong photobactericidal activity against Gram-positive as well as Gram-negative bacteria. It was further shown that this conjugate was able to strongly stick to the cell walls of either kind of strain, thus helping to inactivate bacteria through the production of reactive oxygen species under light irradiation.

Bacterial lipid membranes as promising targets to fight antimicrobial resistance, molecular foundations and illustration through the renewal of aminoglycoside antibiotics and emergence of amphiphilic aminoglycosides

Membrane anionic lipids as attractive targets in the design of amphiphilic antibacterial drugs active against resistant bacteria: molecular foundations and examples.

Polymyxin E Induces Rapid Paenibacillus polymyxa Death by Damaging Cell Membrane while Ca2+ Can Protect Cells from Damage

Polymyxin E, produced by Paenibacillus polymyxa, is an important antibiotic normally against Gram-negative pathogens. In this study, we found that polymyxin E can kill its producer P. polymyxa, a Gram-positive bacterium, by disrupting its cell membrane. Membrane damage was clearly revealed by detecting the leakage of intracellular molecules. The observation using scanning electron microscopy also supported that polymyxin E can destroy the cell membrane and cause an extensive cell surface alteration. On the other hand, divalent cations can give protection against polymyxin E. Compared with Mg²⁺, Ca²⁺ can more effectively alleviate polymyxin E-induced damage to the cell membrane, thus remarkably increasing the P. polymyxa survival. Our findings would shed light on a not yet described bactericidal mechanism of polymyxin E against Gram-positive bacteria and more importantly the nature of limited fermentation output of polymyxin E from P. polymyxa.

Antibacterial mechanisms of polymyxin and bacterial resistance

Multidrug resistance in pathogens is an increasingly significant threat for human health. Indeed, some strains are resistant to almost all currently available antibiotics, leaving very limited choices for antimicrobial clinical therapy. In many such cases, polymyxins are the last option available, although their use increases the risk of developing resistant strains. This review mainly aims to discuss advances in unraveling the mechanisms of antibacterial activity of polymyxins and bacterial tolerance together with the description of polymyxin structure, synthesis, and structural modification. These are expected to help researchers not only develop a series of new polymyxin derivatives necessary for future medical care, but also optimize the clinical use of polymyxins with minimal resistance development.

Colistin in burn intensive care: back to the future?

Colistin is a venerable antibiotic whose fortunes have been revived by its excellent activity, the diminishing output of novel clinically effective antibiotics and the increasing importance of MDR infection in burn surgery, both in the civilian and military arenas. This review synthesizes current evidence on the usage of colistin in burn surgery including the structure-activity relationship; dosing, pharmacokinetics/pharmacodynamic (PK/PD), analytic methods, resistance and current research efforts into the redevelopment of this antibiotic, to distil recommendations for future research and clinical efficacy.