The wide-spreading of multidrug resistance poses a significant threat to human and animal health. Although antimicrobial peptides (AMPs) show great potential application, their instability has severely limited their clinical application. Here, self-assembled AMPs composed of multiple modules based on the principle of associating natural marine peptide N6 with ß-sheet-forming peptide were designed. It is noteworthy that one of the designed peptides, FFN could self-assemble into nanoparticles at 35.46 µM and achieve a dynamic transformation from nanoparticles to nanofibers in the presence of bacteria, resulting in a significant increase in stability in trypsin and tissues by 1.72–57.5 times compared to that of N6. Additionally, FFN exhibits a broad spectrum of antibacterial activity against multidrug-resistant (MDR) gram-positive (G+) and gram-negative (G−) bacteria with Minimum inhibitory concentrations (MICs) as low as 2 µM by membrane destruction and complemented by nanofiber capture. In vivo mouse mastitis infection model further confirmed the therapeutic potential and promising biosafety of the self-assembled peptide FFN, which can effectively alleviate mastitis caused by MDR Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), and eliminate pathogenic bacteria. In conclusion, the design of peptide-based nanomaterials presents a novel approach for the delivery and clinical translation of AMPs, promoting their application in medicine and animal husbandry.

NZ2114 and MP1102 are novel plectasin-derived peptides with potent activity against Gram-positive bacteria. The antibacterial characteristics and mechanism of NZ2114 and MP1102 against gas gangrene-associated Clostridium perfringens were studied for the first time. The minimal inhibitory concentration and minimal bactericidal concentration of NZ2114 and MP1102 against resistant C. perfringens type A strain CVCC 46 were 0.91 μM. Based on the fractional inhibitory concentration index (FICI) result, an additive or synergic effect was observed between NZ2114 (FICI = 0.5~0.75) or MP1102 (FICI = 0.375~1.0) and antibiotics. The flow cytometry, scanning and transmission electron microscopy analysis showed that both NZ2114 and MP1102 induced obviously membrane damage, such as the leakage of cellular materials, partial disappearance of the cell membrane and membrane peeling, as well as retracting cytoplasm and ghost cell. The gel retardation and circular dichroism (CD) detection showed that NZ2114 and MP1102 could bind to C. perfringens genomic DNA and change the DNA conformation. Moreover, NZ2114 also interfered with the double helix and unwind the genomic DNA. The cell cycle analysis showed that C. perfringens CVCC 46 cells exposed to NZ2114 and MP1102 were arrested at the phase I. These data indicated that both NZ2114 and MP1102 have potential as new antimicrobial agents for gas gangrene infection resulting from resistant C. perfringens.

The infections caused by antibiotic multidrug-resistant bacteria seriously threaten human health. To prevent and cure the infections caused by multidrug-resistant bacteria, new antimicrobial agents are required. Antimicrobial peptides are ideal therapy candidates for antibiotic-resistant pathogens. However, due to high production costs, novel methods of large-scale production are urgently needed. The novel plectasin-derived antimicrobial peptide-MP1102 gene was constitutively expressed under the control of the GAP promoter. The optimum carbon source and concentration were determined, and 4% glucose (w/v) was initially selected as the best carbon source. Six media were assayed for the improved yield of recombinant MP1102 (rMP1102). The total protein and rMP1102 yield was 100.06 mg/l and 42.83 mg/l, which was accomplished via the use of medium number 1. The peptone and yeast extract from Hongrun Baoshun (HRBS, crude industrial grade, Beijing, China) more effectively improved the total protein and the yield of rMP1102 to 280.41 mg/l and 120.57 mg/l compared to 190.26 mg/l and 78.01 mg/l that resulted from Oxoid (used in the research). Furthermore, we observed that the total protein, antimicrobial activity and rMP1102 yield from the fermentation supernatant increased from 807.42 mg/l, 384,000 AU/ml, and 367.59 mg/l, respectively, in pH5.0 to 1213.64 mg/l, 153,600 AU/ml and 538.17 mg/ml, respectively in pH 6.5 in a 5-l fermenter. Accordingly, the productivity increased from 104464 AU/mg rMP1102 in pH 5.0 to a maximum of 285412 AU/mg rMP1102 in pH 6.5. Finally, the recombinant MP1102 was purified with a cation-exchange column with a yield of 376.89 mg/l, 96.8% purity, and a molecular weight of 4382.9 Da, which was consistent with its theoretical value of 4383 Da. It’s the highest level of antimicrobial peptides expressed in Pichia pastoris using GAP promoter so far. These results provide an economical method for the high-level production of rMP1102 under the control of the GAP promoter.

With the accelerating growth of antimicrobial resistance (AMR), there is an urgent need for new antimicrobial agents with low or no AMR. Antimicrobial peptides (AMPs) have been extensively studied as alternatives to antibiotics (ATAs). Coupled with the new generation of high-throughput technology for AMP mining, the number of derivatives has increased dramatically, but manual running is time-consuming and laborious. Therefore, it is necessary to establish databases that combine computer algorithms to summarize, analyze, and design new AMPs. A number of AMP databases have already been established, such as the Antimicrobial Peptides Database (APD), the Collection of Antimicrobial Peptides (CAMP), the Database of Antimicrobial Activity and Structure of Peptides (DBAASP), and the Database of Antimicrobial Peptides (dbAMPs). These four AMP databases are comprehensive and are widely used. This review aims to cover the construction, evolution, characteristic function, prediction, and design of these four AMP databases. It also offers ideas for the improvement and application of these databases based on merging the various advantages of these four peptide libraries. This review promotes research and development into new AMPs and lays their foundation in the fields of druggability and clinical precision treatment.

Edwardsiella tarda can cause fatal gastro-/extraintestinal diseases in fish and humans. Overuse of antibiotics has led to antibiotic resistance and contamination in the environment, which highlights the need to find new antimicrobial agents. In this study, the marine peptide-N6 was amidated at its C-terminus to generate N6NH2. The antibacterial activity of N6 and N6NH2 against E. tarda was evaluated in vitro and in vivo; their stability, toxicity and mode of action were also determined. Minimal inhibitory concentrations (MICs) of N6 and N6NH2 against E. tarda were 1.29–3.2 μM. Both N6 and N6NH2 killed bacteria by destroying the cell membrane of E. tarda and binding to lipopolysaccharide (LPS) and genomic DNA. In contrast with N6, N6NH2 improved the stability toward trypsin, reduced hemolysis (by 0.19% at a concentration of 256 μg/mL) and enhanced the ability to penetrate the bacterial outer and inner membrane. In the model of fish peritonitis caused by E. tarda, superior to norfloxacin, N6NH2 improved the survival rate of fish, reduced the bacterial load on the organs, alleviated the organ injury and regulated the immunity of the liver and kidney. These data suggest that the marine peptide N6NH2 may be a candidate for novel antimicrobial agents against E. tarda infections.

Insect defensins are promising candidates for the development of potent antimicrobials against antibiotic-resistant Staphylococcus aureus (S. aureus). An insect defensin DLP4, isolated from the hemolymph of Hermetia illucens larvae, showed low antimicrobial activity against Gram-positive (G+) pathogens and high cytotoxicity, which limited its effective therapeutic application. To obtain more potent and low cytotoxicity molecules, a series of peptides were designed based on the DLP4 template by changing the conservative site, secondary structure, charge, or hydrophobicity. Among them, a variant designated as ID13, exhibited strong antibacterial activity at low MICs values of 4-8 μg/mL to G+ pathogens (S. aureus: 4 μg/mL, Staphylococcus epidermidis: 8 μg/mL, Streptococcus pneumoniae: 4 μg/mL, Streptococcus suis: 4 μg/mL), which were lower than those of DLP4 (S. aureus: 16 μg/mL, S. epidermidis: 64 μg/mL, S. pneumoniae: 32 μg/mL, S. suis: 16 μg/mL), and cytotoxicity of ID13 (71.4% viability) was less than that of DLP4 (63.8% viability). ID13 could penetrate and destroy the cell membrane of S. aureus CVCC 546, resulting in an increase in the potassium ion leakage; it bound to genomic DNA (gDNA) and lead to the change of gDNA conformation. After treatment with ID13, perforated, wrinkled, and collapsed S. aureus CVCC 546 cells were observed in electron microscopy. Additionally, ID13 killed over 99.99% of S. aureus within 1 h, 2×MIC of ID13 induced a postantibiotic effect (PAE) of 12.78±0.28 h, and 10 mg/kg ID13 caused a 1.8 log10 (CFU/g) (CFU: Colony-Forming Unit) reduction of S. aureus in infected mouse thighs muscles and a downregulation of TNF-α, IL-6 and IL-10 levels, which were superior to those of DLP4 or vancomycin. These findings indicate that ID13 may be a promising peptide antimicrobial agent for therapeutic application.