Synthetic Antimicrobial Polymers in Combination Therapy: Tackling Antibiotic Resistance

Antimicrobial peptides: mechanism of action, activity and clinical potential

The management of bacterial infections is becoming a major clinical challenge due to the rapid evolution of antibiotic resistant bacteria. As an excellent candidate to overcome antibiotic resistance, antimicrobial peptides (AMPs) that are produced from the synthetic and natural sources demonstrate a broad-spectrum antimicrobial activity with the high specificity and low toxicity. These peptides possess distinctive structures and functions by employing sophisticated mechanisms of action. This comprehensive review provides a broad overview of AMPs from the origin, structural characteristics, mechanisms of action, biological activities to clinical applications. We finally discuss the strategies to optimize and develop AMP-based treatment as the potential antimicrobial and anticancer therapeutics.

Macromolecular Nanotherapeutics and Antibiotic Adjuvants to Tackle Bacterial and Fungal Infections

The escalating rise in the population of multidrug-resistant (MDR) pathogens coupled with their biofilm forming ability has struck the global health as nightmare. Alongwith the threat of aforementioned menace, the sluggish development of new antibiotics and the continuous deterioration of the antibiotic pipeline has stimulated the scientific community toward the search of smart and innovative alternatives. In near future, membrane targeting antimicrobial polymers, inspired from antimicrobial peptides, can stand out significantly to combat against the MDR superbugs. Many of these amphiphilic polymers can form nanoaggregates through self-assembly with superior and selective antimicrobial efficacy. Additionally, these macromolecular nanoaggregrates can be utilized to engineer smart antibiotic-delivery system for on-demand drug-release, exploiting the infection site's micoenvironment. This strategy substantially increases the local concentration of antibiotics and reduces the associated off-target toxicity. Furthermore, amphiphilc macromolecules can be utilized to rejuvinate obsolete antibiotics to tackle the drug-resistant infections. This review article highlights the recent developments in macromolecular architecture to design numerous nanostructures with broad-spectrum antimicrobial activity, their application in fabricating smart drug delivery systems and their efficacy as antibiotic adjuvants to circumvent antimicrobial resistance. Finally, the current challenges and future prospects are briefly discussed for further exploration and their practical application in clinical settings.

The contribution of nano-based strategies in overcoming ceftriaxone resistance: a literature review

Antimicrobial drug resistance, including resistance to multiple antibiotics, is continuously increasing. According to research findings, many bacteria resistant to other antibiotics were susceptible to ceftriaxone. However, over the last few years, ceftriaxone resistance has become growing and extremely worrisome challenge to the global healthcare system and several strategies have been initiated to contain the spread of antimicrobial drug resistance. Its extended use for therapeutic or preventative measures in humans and farm animals resulted in the development and spread of resistance. Recent advances in nanotechnology also offer novel formulations based on distinct types of nanostructure particles with different sizes and shapes, and flexible antimicrobial properties. For ceftriaxone, several nanostructured formulations through conjugation, intercalation, encapsulation with lipid carrier, and polymeric films have been investigated by different groups with promising results in combating the development of resistance. This review addressed the existing knowledge and practice on the contribution of nano-based delivery approaches in overcoming ceftriaxone resistance. Evidences have been generated from published research articles using major search electronic databases such as PubMed, Medline, Google Scholar, and Science Direct.

Enhanced Antibacterial and Anti-Biofilm Activities of Antimicrobial Peptides Modified Silver Nanoparticles

Background

The biofilms could protect bacteria from antibiotics and promote the production of drug-resistant strains, making the bacteria more difficult to be eradicated. Thus, we developed an AMP@PDA@AgNPs nanocomposite, which is formed by modifying silver nanoparticles (AgNPs) with antimicrobial peptides (AMP) modified nanocomposite to destroy biofilm in this study.

Methods

The AMP@PDA@AgNPs nanocomposite was prepared with polymerization method and characterized by using ultraviolet-visible (UV-vis) spectroscopy, dynamic light scattering (DLS), Fourier transform-infrared spectroscopy (FT-IR), and transmission electron microscope (TEM). The antibacterial effects of the nanocomposite were investigated by using agar diffusion method and minimum inhibitory concentration (MIC) test. The quantitative analysis of the biofilm formation by the nanocomposite was conducted using crystal violet staining and confocal laser scanning microscope (CLSM).

Results

The DLS and TEM analysis showed it was a spherical nanocomposite with 200 nm size and well dispersed . The results of UV-vis and FT-IR confirmed the presence of AMP and AgNPs. The nanocomposite had an excellent biocompatibility at 100 μg/mL. And the AMP@PDA@AgNPs nanocomposite showed superior antimicrobial activity against both Gram-negative (E. coli, P. aeruginosa) and Gram-positive (S. aureus) bacteria than AgNPs or AMP. Importantly, the mRNA expression of biofilm-related genes were decreased under the action of the nanocomposites.

Conclusion

An AMP@PDA@AgNPs nanocomposite with good biocompatibility was successfully prepared. The nanocomposite could destruct bacterial biofilms by inhibiting the expression of biofilm-related genes. The synergistic strategy of AMPs and AgNPs could provide a new perspective for the treatment of bacterial infection.

Photoresponsive Micelles Enabling Codelivery of Nitric Oxide and Formaldehyde for Combinatorial Antibacterial Applications

It is of particular interest to develop new antibacterial agents with low risk of drug resistance development and low toxicity toward mammalian cells to combat pathogen infections. Although gaseous signaling molecules (GSMs) such as nitric oxide (NO) and formaldehyde (FA) have broad-spectrum antibacterial performance and the low propensity of drug resistance development, many previous studies heavily focused on nanocarriers capable of delivering only one GSM. Herein, we developed a micellar nanoparticle platform that can simultaneously deliver NO and FA under visible light irradiation. An amphiphilic diblock copolymer of poly(ethylene oxide)-b-poly(4-((2-nitro-5-(((2-nitrobenzyl)oxy)methoxy)benzyl)(nitroso)amino)benzyl methacrylate) (PEO-b-PNNBM) was successfully synthesized through atom transfer radical polymerization (ATRP). The resulting diblock copolymer self-assembled into micellar nanoparticles without premature NO and FA leakage, whereas they underwent phototriggered disassembly with the corelease of NO and FA. We showed that the NO- and FA-releasing micellar nanoparticles exhibited a combinatorial antibacterial performance, efficiently killing both Gram-negative (e.g., Escherichia coli) and Gram-positive (e.g., Staphylococcus aureus) bacteria with low toxicity to mammalian cells and low hemolytic property. This work provides new insights into the development of GSM-based antibacterial agents.

Polymeric antibacterial materials: design, platforms and applications

Over the past decades, the morbidity and mortality caused by pathogen invasion remain stubbornly high even though medical care has increasingly improved worldwide. Besides, impacted by the ever-growing multidrug-resistant bacterial strains, the crisis owing to the abuse and misuse of antibiotics has been further exacerbated. Among the wide range of antibacterial strategies, polymeric antibacterial materials with diversified synthetic strategies exhibit unique advantages (e.g., their flexible structural design, processability and recyclability, tuneable platform construction, and safety) for extensive antibacterial fields as compared to low molecular weight organic or inorganic antibacterial materials. In this review, polymeric antibacterial materials are summarized in terms of four structure styles and the most representative material platforms to achieve specific antibacterial applications. The superiority and defects exhibited by various polymeric antibacterial materials are elucidated, and the design of various platforms to elevate their efficacy is also described. Moreover, the application scope of polymeric antibacterial materials is summarized with regard to tissue engineering, personal protection, and environmental security. In the last section, the subsequent challenges and direction of polymeric antibacterial materials are discussed. It is highly expected that this critical review will present an insight into the prospective development of antibacterial functional materials.

Conjugated polymer nanostructures displaying highly photoactivated antimicrobial and antibiofilm functionalities

This work reports the use of conjugated polymer nanostructures (CPNs) as photoactivated antimicrobial compounds against Gram-positive and Gram-negative microorganisms. Two representative CPNs of polythiophene (PEDOT) and polyaniline (PANI) were prepared as nanofibres with an average diameter of 40 nm and length in the micrometer range. Both CPNs exhibited strong antimicrobial activity under UVA irradiation with the same fluence rate as the UVA component of the solar spectrum. The effect was tested using the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli. The reduction of colony forming units (CFUs) reached >6 log for PEDOT concentrations as low as 33 ng mL-1. For PEDOT nanofibers, a complete inhibition of S. aureus and E. coli growth was reached at 883 ng mL-1 and 333 ng mL-1 respectively. The photoactivation effect of PANI nanofibres on S. aureus and E. coli was also high, with a CFU reduction of about 7 log and 4 log respectively for an exposure concentration of 33 ng mL-1. The antimicrobial activity was only high under light irradiation and was almost negligible for bulk PEDOT and PANI. The effect of polymeric nanofibers could be attributed to the photoinduced generation of reactive oxygen species, which may induce cell membrane damage, eventually leading to bacterial impairment and inhibition of their biofilm forming capacity. CPN PEDOT and PANI coatings were able to keep surfaces free of bacterial attachment and growth even after 20 h of previous contact with exponentially growing cultures in the dark. PEDOT and PANI CPNs demonstrated good cytocompatibility with human fibroblasts and the absence of hemolytic activity. The materials demonstrated advantages in terms of broad antibacterial spectrum, biofilm inhibition, and the absence of acute toxicity for biomedical applications.