Antibacterial Activity Of Antimicrobial Peptides Research Articles

Evaluation of the synergistic potential and mechanisms of action for de novo designed cationic antimicrobial peptides

Antimicrobial peptides (AMPs) have emerged as promising candidates in combating antimicrobial resistance – a growing issue in healthcare. However, to develop AMPs into effective therapeutics, a thorough analysis and extensive investigations are essential. In this study, we employed an in silico approach to design cationic AMPs de novo, followed by their experimental testing. The antibacterial potential of de novo designed cationic AMPs, along with their synergistic properties in combination with conventional antibiotics was examined. Furthermore, the effects of bacterial inoculum density and metabolic state on the antibacterial activity of AMPs were evaluated. Finally, the impact of several potent AMPs on E. coli cell envelope and genomic DNA integrity was determined. Collectively, this comprehensive analysis provides insights into the unique characteristics of cationic AMPs.

Screening and Preparation of a Short Chain Antimicrobial Peptide SFPAS

A short chain antimicrobial peptide SFPAS was screened by cell membrane chromatography combined with one bead and one object method. The membrane chromatographic fillers with particle size of about 2 μm were prepared. Through field emission scanning electron microscope observation, we could see the successful preparation of membrane chromatographic packing. Then, the antibacterial activity of antimicrobial peptides was tested, and it was found that the selected antimicrobial peptides had obvious antibacterial activity and could effectively kill Staphylococcus aureus and Escherichia coli.

Broad-spectrum hybrid antimicrobial peptides derived from PMAP-23 with potential LPS binding ability

Antimicrobial peptides, as an integral part of the innate immune system, kill bacteria through a special mechanism of action, making them less susceptible to drug resistance. However, Lipopolysaccharide (LPS) as the permeation barrier on the bacterial membrane, inhibits the antibacterial activity of antimicrobial peptides and triggers the inflammatory response. GWKRKRFG is an LPS binding sequence with a β-boomerang motif that can be linked to antimicrobial peptides to enhance their LPS affinity and reduce the possibility of LPS-induced inflammatory responses. In this study, a series of hybrid peptides were designed by conjugating the reported LPS binding sequence to the C-/N-terminal sequences of the natural porcine antimicrobial peptide PMAP-23 to increase the LPS affinity of peptides. Among all the designed hybrid peptides, 4R-PP-G8 showed the best antibacterial activity, nonhemolytic activity, and excellent cell selectivity. The presence of LPS not only induced the secondary structure transformation of 4R-PP-G8 from a random structure to an α-helical structure but also reduced the antibacterial activity of 4R-PP-G8 in a dose-dependent manner, indicating the excellent binding ability of 4R-PP-G8 to LPS. The LPS/LTA binding assay further verified the interaction between the peptide and LPS. The membrane permeability test verified that 4R-PP-G8 possessed a strong capability to penetrate the bacterial membrane after interacting with LPS. More direct membrane disruption was observed under FE-SEM and TEM. In conclusion, we provided a simple and efficient method to improve the LPS binding ability of antimicrobial peptides and enhance their antimicrobial activity, resulting in the peptide 4R-PP-G8 with clinical application potential.

Loot a burning house: Strategies to enhance the antibacterial activity of antimicrobial peptides

In recent years, antimicrobial peptides (AMPs) are gaining remarkable interest in their application in agriculture and food industry. Thanks to the bacteria cell membrane permeabilization capability of AMPs, treatment of AMP potentially allows the entry of a secondary antimicrobial agent into the bacterial cells. The fractional inhibitory concentration (FIC) assay showed the synergy of antibacterial effect of AMPs in combination with citric acid (CA) with ΣFICI values of 0.3 for IDR-1018 and 0.4 for 1018-K6 on Salmonella enterica. Under scanning electron microscopy (SEM), structural damages of the Salmonella cells were observed after both treatment of 1018-K6 and CA but in different manners. When 1018-K6 and CA were used in combination, the cells demonstrated more pronounced deformation than the individual treatment. This combination demonstrated great potentials when applied onto fresh produce. After 120 min at room temperature, 2.5 μmol L−1 1018-K6 and 0.1% CA inactivated Salmonella on the blueberries from 4.14 ± 0.05 log CFU/berry to 2.26 ± 0.39 log CFU/berry. After 1 day storage at 4 °C, the Salmonella load on the treated berries further decreased to 1.76 ± 0.39 log CFU/berry, whereas from day 2 onwards, the Salmonella was below the enumeration limit (1.40 log CFU/berry). Last, this strategy of enhancing the antibacterial activity of AMPs is also applicable to other bacteria (as tested on Escherichia coli) and other secondary antimicrobial agents (as tested on rose bengal).

Antimicrobial Peptide-Loaded Gelatinase-Responsive Photothermal Nanogel for the Treatment of Staphylococcus aureus-Infected Wounds.

As the most common pathogen of community and nosocomial infection, the resistance of Staphylococcus aureus (S. aureus) to traditional antibiotics is still increasing with years. Although the potent antibacterial activity of antimicrobial peptides (AMPs) has been widely confirmed, the unpredictable cytotoxicity remains the biggest obstacle to their clinical application. The development of a targeted drug delivery system for S. aureus is a practical strategy to ameliorate the inherent limitations of AMPs. In this work, we constructed an AMP release nanogel (cypate-GNPs@Cy3-AMP, CGCA) of S. aureus infection microenvironment using gelatinase nanoparticles (GNPs) for toxicity control and bacterial clearance. Gelatinase present in the infected site degrades GNPs, thus releasing Cy3-AMP in situ to destroy bacterial cells. Cypate modified on the surface of GNPs supports CGCA to generate localized heat under near-infrared (NIR) laser irradiation, which together with AMPs could cause irreversible physical damage to bacteria. In addition, the encapsulation from GNPs not only effectively limited the toxicity of AMPs but also significantly promoted cell proliferation and migration in vitro. In the mouse infection model, CGCA also exhibited excellent effects of bacterial clearance and wound healing, providing a potential direction for the correct use of AMPs.

Identification of New Nitric Oxide-Donating Peptides with Dual Biofilm Eradication and Antibacterial Activities for Intervention of Device-Related Infections.

Implantable medical device-related infections with biofilms have become a significant challenge in clinics. Based on the potential bacteria biofilm dispersing effect of nitric oxide (NO) and the unique antibacterial activity of antimicrobial peptides (AMP), we synthesized five peptides and selected the most potent one to conjugate its N-terminal with a furoxan moiety to offer a hitherto unknown NO-donating antimicrobial peptide (FOTyr-AMP), which exhibited Staphylococcus aureus and Escherichia coli biofilm dispersion and eradication, and potent antibacterial activities in vitro. In an implanted biofilm infection mice model, topical subcutaneous injection of FOTyr-AMP allowed synergetic eradication of bacterial biofilms and potent antibacterial activity, superior to the antibiotic cephalosporin C. Given the low hemolysis effect, little influence on the blood pressure, and potent in vivo efficacy of FOTyr-AMP, it is clear that subcutaneous administration of FOTyr-AMP could be a promising approach for the intervention of medical device-related biofilm infections with desirable safety.

Antimicrobial Activity of the Antibacterial Peptide PMAP-GI24 and Its Analogs

Because of the growing problem of antibiotic resistance, the antibacterial activity of antimicrobial peptides (AMPs) has attracted attention. In this study, two PMAP-GI24 peptide analogs, PMAP-24WW and PMAP-24KK, were synthesized by extending the α-helix and increasing the positive charge of the parental peptide. The antibacterial activities of PMAP-GI24 and its analogs were detected in vitro and in vivo. The results showed that after modification, PMAP-24KK displayed an increased zone of inhibition against Escherichia coli ATCC25922 compared to that of PMAP-GI24. PMAP-24WW had inhibition zones against nine bacterial strains, among which, the antibacterial zones were larger than those of PMAP-GI24 against seven bacterial strains. Furthermore, PMAP-24KK had inhibition zones against ten bacterial strains, and the antibacterial zones were larger than those of PMAP-GI24 against seven bacterial strains. Moreover, in the in vivo efficacy assessment of mice infected with Salmonella enterica serovar choleraesuis C78-1 and Listeria monocytogenes CICC21533, the PMAP-GI24 analogs effectively reduced the number of bacterial and decreased the inflammatory damage in the mouse livers and lungs, thus effectively reducing mortality. This study provides reference data for the clinical design of effective antibiotic alternatives.

Novel activity evaluation and subsequent partial purification of antimicrobial peptides produced by Bacillus subtilis LFB112

The antibacterial activity of antimicrobial peptides produced by strain LFB 112 was determined using the cup-plate method and a standard curve of penicillin. An effective method to evaluate the antimicrobial activity of antibacterial peptides was established. Three active fractions, Fraction A (5.0–5.5 kDa), Fraction B (3.0–3.5 kDa) and Fraction C (400–800 Da), were separated by anion-exchange, reversed phase liquid chromatography (RPLC) and gel filtration chromatography. Fraction A contained an antimicrobial peptide; its partial sequence (LVQSPNGNFAASFVLDGTK), determined by liquid chromatography-mass spectrometry (LC-MS), was homologous with antimicrobial peptide LCI. In addition, there were three major ingredients in fraction B (3,371.811, 3,442.379 and 3,486.596 Da, respectively), and several small peptides (400–800 Da) in fraction C. After purification, the potencies of fractions A, B and C were 188.6, 11,217.26 and 10,290.63 U/mg, respectively. Furthermore, antimicrobial peptides in fraction B, apparently different from known antimicrobial peptides produced by Bacillus subtilis (based on molecular weight), and small (molecular weight 400–800 Da) antimicrobial peptides produced by B. subtilis LFB112 were also identified. Antimicrobial peptides produced by strain LFB112 with high potency against several undesirable bacteria were identified. These compounds have potential as alternatives to known antibiotics.

Glycosaminoglycans inhibit the antibacterial activity of LL-37 in biological fluids

The antibacterial activity of antimicrobial peptides is influenced by various factors such as salt content, pH and the presence of proteins. In this study, we explored the antibacterial action of the human cathelicidin LL-37 in physiologically relevant conditions, i.e. various human wound fluids, human plasma fractions and serum. Radial diffusion assays using Staphylococcus aureus and Escherichia coli were employed for the study of antibacterial effects of LL-37 in the presence of 12 different wound fluids, citrate-, heparin- or EDTA-plasma, or human serum. Glycosaminoglycan content of wound fluids was determined by an Alcian Blue-binding assay. Protein content of wound fluids was measured by the Bradford method. A slot-binding assay was used to study the effects of inhibitors on the interaction between LL-37 and glycosaminoglycans. Five of twelve wound fluids derived from acute wounds showed marked inhibitory effects on the antibacterial action of LL-37. The inhibition was significantly correlated with high glycosaminoglycan content in wound fluid. Analogous to these findings, heparin-plasma strongly inhibited the antibacterial effect of LL-37. The interaction between LL-37 and glycosaminoglycans was abrogated by the cationic polymers DEAE-dextran and chitosan, yielding increased activity of LL-37. Glycosaminoglycan-rich biological fluids inhibit the antibacterial effects of LL-37. Furthermore, polycations that bind to glycosaminoglycans increase the antibacterial activities of endogenous antimicrobial peptides in glycosaminoglycan-containing biological fluids.

Purification and antibacterial activity of antimicrobial peptides of rabbit granulocytes.

Six antimicrobial peptides, corresponding to the family of "lysosomal cationic proteins" described previously by Zeya and Spitznagel (H. I. Zeya and J. K. Spitznagel, J. Bacteriol. 91:750-754, 1966; H. I. Zeya and J. K. Spitznagel, J. Bacteriol. 91:755-762, 1966), were purified from rabbit peritoneal granulocytes by preparative acrylamide gel electrophoresis and reversed-phase high-pressure liquid chromatography. Each of the peptides was of low molecular weight (ca. 4,000) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The two most cationic peptides, NP-1 and NP-2, were active against a broad spectrum of gram-positive and gram-negative bacteria. The remaining four peptides, NP-3A, NP-3B, NP-4, and NP-5, had more selective antibacterial activity. None of the peptides was active against Bordetella bronchiseptica, a common pathogen of domestic rabbits. Antibacterial activity was best expressed at near neutral pH under conditions of low ionic strength.