The Ultrashort Peptide OW: A New Antibiotic Adjuvant

Anti-Pseudomonas aeruginosa activity of natural antimicrobial peptides when used alone or in combination with antibiotics

The World Health Organization has recently published a list of 12 drug-resistant bacteria that posed a significant threat to human health, and Pseudomonas aeruginosa (P. aeruginosa) was among them. In China, P. aeruginosa is a common pathogen in hospital acquired pneumonia, accounting for 16.9-22.0%. It is a ubiquitous opportunistic pathogen that can infect individuals with weakened immune systems, leading to hospital-acquired acute and systemic infections. The excessive use of antibiotics has led to the development of various mechanisms in P. aeruginosa to resist conventional drugs. Thus, there is an emergence of multidrug-resistant strains, posing a major challenge to conventional antibiotics and therapeutic approaches. Antimicrobial peptides are an integral component of host defense and have been found in many living organisms. Most antimicrobial peptides are characterized by negligible host toxicity and low resistance rates, making them become promising for use as antimicrobial products. This review particularly focuses on summarizing the inhibitory activity of natural antimicrobial peptides against P. aeruginosa planktonic cells and biofilms, as well as the drug interactions when these peptides used in combination with conventional antibiotics. Moreover, the underlying mechanism of these antimicrobial peptides against P. aeruginosa strains was mainly related to destroy the membrane structure through interacting with LPS or increasing ROS levels, or targeting cellular components, leaded to cell lysis. Hopefully, this analysis will provide valuable experimental data on developing novel compounds to combat P. aeruginosa.

Dual-Mechanism Glycolipidpeptide with High Antimicrobial Activity, Immunomodulatory Activity, and Potential Application for Combined Antibacterial Therapy

Bacterial drug resistance is becoming increasingly serious, and it is urgent to develop effective antibacterial drugs. Antimicrobial peptides (AMPs), as potential candidates against bacteria, have a broad prospect for development. Herein, a series of AMPs with biological characteristics (net positive charge, amphiphilicity, and α-helix), an AXA motif recognized by membrane bound serine protease type I signal peptidases (SPase I), an FLPII motif to reduce hemolysis, and a monosaccharide motif to improve the stability and activity were designed and synthesized, and among which, the glycolipidpeptide GLP6 (glycosylated LP6 lipopeptide) had excellent antibacterial and immunomodulatory activity, good stability and biocompatibility, and excellent biofilm eradication and membrane penetrating activity. The positively charged spherical aggregates formed by self-assembly of GLP6 could encapsulate tetracycline (TC) to form GLP6@TC with a sustained-release effect, which could enhance the sensitivity of bacteria to the antibiotic and realize combined sterilization. The results of acute peritonitis and bacterial keratitis showed that GLP6@TC had a good combined antibacterial effect and the ability to inhibit interleukin-2 (IL-2), which could significantly reduce the inflammatory response while treating bacterial infection, and it had great potential for application. The results of computer molecular docking showed the AXA motif could effectively bind to SPase I, which was consistent with the results of biological experiments. In general, the study could provide a perspective for the design of AMPs and combined antibacterial therapy.

Metformin as a Potential Adjuvant Antimicrobial Agent Against Multidrug Resistant Bacteria

Introduction

The continuous increase in the incidence of bacterial resistance to existing antibiotics represents a worldwide health burden. A surrogate strategy to combat such crisis is to find compounds that restore the antimicrobial activity of the already existing antibiotics against multidrug resistant bacteria. Metformin is a commonly used antidiabetic medication. It has proven benefits in other diseases including cancer, aging-related and infectious diseases. In this study, the potential effect of metformin as an adjuvant therapy to antibiotics was investigated.

Methods

Two multidrug resistant bacterial strains were used; methicillin-resistant Staphylococcus aureus (MRSA; ATCC 33,591) and multidrug resistant Pseudomonas aeruginosa (ATCC BAA-2114). To assess its efficacy, metformin was combined with several antibiotics: levofloxacin, chloramphenicol, rifampicin, ampicillin, and doxycycline. The antibacterial effect of metformin was tested using the micro broth dilution method. The minimum inhibitory concentration (MIC) was also measured. Cytotoxicity studies were also performed on mammalian cells to assess its safety.

Results

Metformin exhibited an antibacterial effect when combined with the antibiotics on the two tested strains. It also showed low toxicity on the mammalian cells. Moreover, synergetic studies showed that metformin enhanced the effect of the combined antibiotics, as these combinations provide either a synergistic or additive effect with significant reduction in the MIC.

Conclusion

Metformin exerts an adjuvant antibacterial effect; thus, it could be a possible candidate as an adjuvant therapy to reduce antimicrobial resistance.