Design, expression, and characterization of a novel cecropin A-derived peptide with high antibacterial activity

Endolysins as Effective Agents for Decontaminating S. typhimurium, E. coli, and L. monocytogenes on Mung Bean Seeds

Seeds are a major source of contamination by foodborne pathogens such as Salmonella typhimurium, Escherichia coli, and Listeria monocytogenes, significantly increasing the risk of foodborne diseases associated with fresh produce like sprouts. In this study, we described novel endolysins and the engineered variants that exhibited potent bactericidal activity against these pathogens. These endolysins demonstrated strong bactericidal effects independently of outer membrane permeabilizers, effectively killing S. typhimurium, E. coli, and L. monocytogenes to undetectable levels (>4-log kill) at concentrations as low as 12.5 μg/mL. The enzymes retained their activity in complex environments, such as a wide range of temperatures (4-100 °C), pH values (4-10), serum concentrations (0-50%), and sodium chloride concentrations (0-500 mM). Furthermore, their rapid bactericidal kinetics, excellent storage stability (>18 months), and broad-spectrum antimicrobial activity enhanced their potential for application. These endolysins remained effective against stationary-phase bacteria and biofilm-forming bacteria, achieving more than 99% biofilm eradication at 200 μg/mL. Notably, at concentrations as low as 50 μg/mL, these enzymes completely decontaminated foodborne pathogens in a mung bean seed model contaminated with 4-5 log CFU of bacteria. This study is the first to report the successful use of lysins to control both Gram-negative and Gram-positive pathogens on mung bean seeds.

Natural peptides and their synthetic congeners acting against Acinetobacter baumannii through the membrane and cell wall: latest progress

Acinetobacter baumannii is one of the deadliest Gram-negative bacteria (GNB), responsible for 2-10% of hospital-acquired infections. Several antibiotics are used to control the growth of A. baumannii. However, in recent decades, the abuse and misuse of antibiotics to treat non-microbial diseases have led to the emergence of multidrug-resistant A. baumannii strains. A. baumannii possesses a complex cell wall structure. Cell wall-targeting agents remain the center of antibiotic drug discovery. Notably, the antibacterial drug discovery intends to target the membrane of the bacteria, offering several advantages over antibiotics targeting intracellular systems, as membrane-targeting agents do not have to travel through the plasma membrane to reach the cytoplasmic targets. Microorganisms, insects, and mammals produce antimicrobial peptides as their first line of defense to protect themselves from pathogens and predators. Importantly, antimicrobial peptides are considered potential alternatives to antibiotics. This communication summarises the recently identified peptides of natural origin and their synthetic congeners acting against the A. baumannii membrane by cell wall disruption.

Evaluation of the Synergistic Antimicrobial Activity of Essential Oils and Cecropin A Natural Peptide on Gram-Negative Bacteria

In an era dominated by the phenomenon of antibiotic resistance, it is increasingly important to look for alternatives to synthetic antibiotics. In light of these considerations, the synergistic use of essential oils and Antimicrobial Peptides (AMPs) seems a viable strategy. In this study, we assessed the Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Fractional Inhibitory Concentration (FIC) of three Essential Oils (EOs): winter savory (Satureja montana), bergamot (Citrus bergamia) and cinnamon (Cinnamomum zeylanicum) and of the insect antimicrobial peptide Cecropin A (CecA), alone and in combination with EOs, against two Gram-negative ATCC bacterial strains: Escherichia coli and Salmonella enterica serovar Typhimurium. The MIC results showed that winter savory EO (SmEO) and cinnamon EO (CzEO) exhibited the strongest antibacterial activity against both bacterial strains, whereas bergamot EO (CbEO) and CecA demonstrated comparatively lower antibacterial efficacy. These results were also confirmed by the MBC values. The FIC Indices (FICI) revealed that the most effective synergies were observed with the combinations SmEO/CzEO and SmEO/CbEO against E. coli, while against S. enterica Typhimurium the best combinations were CbEO/CzEO and SmEO/CzEO. Regarding CecA, although it was not the most efficient agent either individually or in combination, it is noteworthy that, when combined, it exhibited antibacterial activity even at a 1:64 dilution.

Aqueous-phase dual-functional chiral perovskites for hydrogen sulfide (H2S) detection and antibacterial applications in Escherichia coli

Perovskite nanocrystals (PNCs) have attracted extensive attention for their potential applications in biology. However, only a handful of PNCs have been scrutinized in the biological domain due to issues such as instability, poor dispersion, and size inhomogeneity in polar solvents. The development of dual-functional perovskite nanomaterials with hydrogen sulfide (H2S) sensing and antibacterial capabilities is particularly intriguing. In this study, we prepared chiral quasi-two-dimensional (quasi-2D) perovskite nanomaterials, Bio(S-PEA)2CsPb2Br7 and Bio(R-PEA)2CsPb2Br7, that were uniformly dispersed in aqueous media. The effective encapsulation of methoxypolyethylene glycol amine (mPEG-NH2) improved water stability and uniformity of particle size. Circular dichroism (CD) signals were created by the successful insertion of chiral cations. These perovskites as probes showed a rapid and sensitive fluorescence quenching response to H2S, and the effect of imaging detection was observed at the Escherichia coli (E. coli) level. As antibacterial agents, their pronounced positive charge properties facilitated membrane lysis and subsequent E. coli death, indicating a significant antibacterial effect. This work has preliminary explored the application of chiral perovskites in biology and provides insight into the development of bifunctional perovskite nanomaterials for biological applications.

Interaction of Cecropin A (1-7) Analogs with DNA Analyzed by Multi-spectroscopic Methods

Cecropin A (1-7) is a cationic antimicrobial peptide which contain lots of basic amino acids. To understand the effect of basic amino acids on cecropin A (1-7), analogues CA2, CA3 and CA4 which have more arginine or lysine at the N-terminal or C-terminal were designed and synthesized. The interaction of cecropin A (1-7) and its analogs with DNA was studied using ultraviolet-visible spectroscopy, fluorescence spectroscopy and circular dichroism spectroscopy. Multispectral analysis showed that basic amino acids improved the interaction between the analogues and DNA. The interaction between CA4 and DNA is most pronounced. Fluorescence spectrum indicated that Ksv value of CA4 is 1.19 × 105  L mol-1 compared to original peptide cecropin A (1-7) of 3.73 × 104  L mol-1. The results of antimicrobial experiments with cecropin A (1-7) and its analogues showed that basic amino acids enhanced the antimicrobial effect of the analogues. The antimicrobial activity of CA4 against E. coli was eightfold higher than that of cecropin A (1-7). The importance of basic amino acid in peptides is revealed and provides useful information for subsequent studies of antimicrobial peptides.

Cecropin AD reduces viral load and inflammatory response against H9N2 avian influenza virus in chickens

Introduction

This study focuses on evaluating the therapeutic efficacy of cecropin AD, an antimicrobial peptide, against H9N2 avian influenza virus (AIV) in chickens. Given the global impact of H9N2 AIV on poultry health, identifying effective treatments is crucial.

Methods

To assess the impact of cecropin AD, we conducted in vivo experiments involving 108 5-week-old chickens divided into control, infected, and various treatment groups based on cecropin AD dosage levels (high, medium, and low). The methodologies included hemagglutination (HA) tests for viral titers, histopathological examination and toluidine blue (TB) staining for lung pathology, real-time PCR for viral detection, and enzyme-linked immunosorbent assays for measuring serum levels of inflammatory markers.

Results

The findings revealed that cecropin AD substantially reduced lung pathology and viral load, especially at higher dosages, comparing favorably with the effects seen from conventional treatments. Moreover, cecropin AD effectively modulated mast cell activity and the levels of inflammatory markers such as IL-6, TNF-α, IFN-γ, and 5-HT, indicating its potential to diminish inflammation and viral spread.

Discussion

Cecropin AD presents a significant potential as an alternative treatment for H9N2 AIV in chickens, as evidenced by its ability to lessen lung damage, decrease viral presence, and adjust immune responses. This positions cecropin AD as a promising candidate for further exploration in the management of H9N2 AIV infections in poultry.

Advances in screening, synthesis, modification, and biomedical applications of peptides and peptide aptamers

Peptides and peptide aptamers have emerged as promising molecules for a wide range of biomedical applications due to their unique properties and versatile functionalities. The screening strategies for identifying peptides and peptide aptamers with desired properties are discussed, including high-throughput screening, display screening technology, and in silico design approaches. The synthesis methods for the efficient production of peptides and peptide aptamers, such as solid-phase peptide synthesis and biosynthesis technology, are described, along with their advantages and limitations. Moreover, various modification techniques are explored to enhance the stability, specificity, and pharmacokinetic properties of peptides and peptide aptamers. This includes chemical modifications, enzymatic modifications, biomodifications, genetic engineering modifications, and physical modifications. Furthermore, the review highlights the diverse biomedical applications of peptides and peptide aptamers, including targeted drug delivery, diagnostics, and therapeutic. This review provides valuable insights into the advancements in screening, synthesis, modification, and biomedical applications of peptides and peptide aptamers. A comprehensive understanding of these aspects will aid researchers in the development of novel peptide-based therapeutics and diagnostic tools for various biomedical challenges.

Screening of a short chain antimicrobial peptide-LKLHI and its application in hydrogels for wound healing

Antibacterial peptides have been widely used in the field of antibacterial due to their biocompatibility. In this work, owing to quickly screen out peptides with antibacterial effects, the bacterial membranes of E. coli and S. aureus were extracted and fixed on self-made silica gel microspheres to prepare bacterial membrane chromatography stationary phase. We successfully screened antimicrobial peptides from a peptide library composed of one-bead-one-compound by bacterial membrane chromatography. The antibacterial peptide has an effective defense effect on gram-positive bacteria, gram-negative bacteria, and fungi. In addition, the antibacterial peptide has almost no hemolysis and cytotoxicity and other excellent biocompatibility and has excellent properties such as stability, broad-spectrum antibacterial, and promotion of wound healing，and HA hydrogel carrier loaded with antimicrobial peptides was prepared, which provided the application direction of antimicrobial dressings for antimicrobial peptides. In summary, this method can screen out polypeptides with antibacterial effects, and the screened-out antibacterial peptides are expected to be applied in clinical applications.

Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Antibiofilm property and multiple action of peptide PEW300 against Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa), an opportunistic pathogen, is often associated with difficulties in treating hospital-acquired infections. Biofilms formed by P. aeruginosa significantly improve its resistance to antimicrobial agents, thereby, posing a great challenge to the combat of P. aeruginosa infection. Antimicrobial peptides (AMPs) have recently emerged as promising antibiofilm agents and increasingly attracting the attention of scientists worldwide. However, current knowledge of their antibiofilm behavior is limited and their underlying mechanism remains unclear. In this study, a novel AMP, named PEW300, with three-point mutations (E9H, D17K, and T33A) from Cecropin A was used to investigate its antibiofilm property and antibiofilm pathway against P. aeruginosa. PEW300 displayed strong antibacterial and antibiofilm activity against P. aeruginosa with no significant hemolysis or cytotoxicity to mouse erythrocyte and human embryonic kidney 293 cells. Besides, the antibiofilm pathway results showed that PEW300 preferentially dispersed the mature biofilm, leading to the biofilm-encapsulated bacteria exposure and death. Meanwhile, we also found that the extracellular DNA was a critical target of PEW300 against the mature biofilm of P. aeruginosa. In addition, multiple actions of PEW300 including destroying the cell membrane integrity, inducing high levels of intracellular reactive oxygen species, and interacting with genomic DNA were adopted to exert its antibacterial activity. Moreover, PEW300 could dramatically reduce the virulence of P. aeruginosa. Taken together, PEW300 might be served as a promising antibiofilm candidate to combat P. aeruginosa biofilms.

Potent antibacterial and antibiofilm activities of TICbf-14, a peptide with increased stability against trypsin

The poor stability of peptides against trypsin largely limits their development as potential antibacterial agents. Here, to obtain a peptide with increased trypsin stability and potent antibacterial activity, TICbf-14 derived from the cationic peptide Cbf-14 was designed by the addition of disulfide-bridged hendecapeptide (CWTKSIPPKPC) loop. Subsequently, the trypsin stability and antimicrobial and antibiofilm activities of this peptide were evaluated. The possible mechanisms underlying its mode of action were also clarified. The results showed that TICbf-14 exhibited elevated trypsin inhibitory activity and effectively mitigated lung histopathological damage in bacteria-infected mice by reducing the bacterial counts, further inhibiting the systemic dissemination of bacteria and host inflammation. Additionally, TICbf-14 significantly repressed bacterial swimming motility and notably inhibited biofilm formation. Considering the mode of action, we observed that TICbf-14 exhibited a potent membrane-disruptive mechanism, which was attributable to its destructive effect on ionic bridges between divalent cations and LPS of the bacterial membrane. Overall, TICbf-14, a bifunctional peptide with both antimicrobial and trypsin inhibitory activity, is highly likely to become an ideal candidate for drug development against bacteria.

Membrane mechanism of temporin-1CEc, an antimicrobial peptide isolated from the skin secretions of Rana chensinensis, and its systemic analogs

Antimicrobial peptides (AMPs) are new and powerful target molecules in the development of new antibacterial agents. Temporin-1CEc, a natural peptide isolated and purified from the skin secretions of the Chinese brown frog Rana chensinensis, exhibits low or no antibacterial activity against gram-negative and gram-positive bacteria, which limits its potential therapeutic use; however, it displays low hemolysis to human erythrocytes. Here, a series of temporin-1CEc analogs was designed and synthesized by amino acid residue substitutions based on cationicity, hydrophobicity, amphipathicity and secondary structure to understand the structure-activity relationships of this peptide in depth. The results showed that all of the analogs, except for 2K and 4K, had significantly improved antibacterial activity against the tested standard bacterial strains and multidrug-resistant bacterial strains compared to temporin-1CEc. 2K2L and 2K4L, but not 4K2L and 4K4L, showed the strongest antibacterial activity compared with their parent peptides 2K and 4K, suggesting that peptide hydrophobicity plays a more important role in antibacterial activity than cationicity for this series of AMPs. However, the antibacterial activity of the 6 Trp-containing analogs of 2K4L decreased with a further increase in hydrophobicity based on the results of 2K4L, indicating that it is more important to balance cationicity and hydrophobicity. Moreover, an increase in AMP hydrophobicity led to hemolysis. Notably, all of the peptides adopted α-helical structures in 50% trifluoroethanol/water and 30 mM SDS solutions. 2K2L and 2K4L displayed broad-spectrum antibacterial activity against sensitive and multidrug-resistant bacteria, effectively killing the tested multidrug resistant strain Staphylococcus epidermidis (MRSE1208). 2K2L and 2K4L were able to increase the permeability of the outer and inner membranes by depolarization and disturb the integration of the cytoplasmic membrane of MRSE1208 cells, leading to leakage of its cellular contents. In addition, 2K2L and 2K4L at low concentrations inhibited biofilm formation and degraded mature 1-day-old MRSE1208 biofilms. Notably, 2K2L and 2K4L inhibited the formation of MRSE1208 biofilms at concentrations below its MIC value, suggesting that the peptide may exert an inhibitory effect through not only direct antimicrobial activity but also a biofilm-specific mechanism. Collectively, these results suggest that 2K2L and 2K4L could be effective antibiotics against multidrug-resistant bacterial strains.

A hemolysin secretion pathway-based novel secretory expression platform for efficient manufacturing of tag peptides and anti-microbial peptides in Escherichia coli

BACKGROUND

Although Escherichia coli has been widely used for the expression of exogenous proteins, the secretory expression in this system is still a big obstacle. As one of the most important secretion pathways, hemolysin A (HlyA) system of E. coli can transport substrates directly from the cytoplasm to extracellular medium without the formation of any periplasmic intermediate, making it an ideal candidate for the development of the secretory production platform for exogenous proteins.

RESULTS

In this work, we developed a novel production platform, THHly, based on the HlyA secretion system, and explored its applications in the efficient preparation and quick detection of tag peptides and anti-microbial peptides. In this novel platform the signal sequence of HlyA is fused to the C-terminal of target peptide, with Tobacco Etch Virus (TEV) protease cleavage site and 6*His tag between them. Five tag peptides displayed good secretory properties in E. coli BL21 (DE3), among which T7 tag and S tag were obtained by two rounds of purification steps and TEV cleavage, and maintained their intrinsic immunogenicity. Furthermore, Cecropin A and Melittin, two different types of widely explored anti-microbial peptides, were produced likewise and verified to possess anti-microbial/anti-tumor bioactivities. No significant bacterial growth inhibition was observed during the fusion protein expression, indicating that the fusion form not only mediated the secretion but also decreased the toxicity of anti-microbial peptides (AMPs) to the host bacteria. To the best of our knowledge, this is the first report to achieve the secretory expression of these two AMPs in E. coli with considerable potential for manufacturing and industrialization purposes.

CONCLUSIONS

The results demonstrate that the HlyA based novel production platform of E. coli allowed the efficient secretory production and purification of peptides, thus suggesting a promising strategy for the industrialized production of peptide pharmaceuticals or reagents.

Analogs of the Cathelicidin-Derived Antimicrobial Peptide PMAP-23 Exhibit Improved Stability and Antibacterial Activity

Antimicrobial peptides (AMPs) have gained interesting as a new type of antimicrobial agent. The cathelicidin-derived antimicrobial peptide PMAP-23 has broad-spectrum antibacterial activity, and to improve its antimicrobial activity, we used amino acid substitution at position 5 or 19 of PMAP-23 to design three analogs, named PMAP-23R (Leu⁵--Arg), PMAP-23I (Thr¹⁹--Ile), and PMAP-23RI (Leu⁵--Arg and Thr¹⁹--Ile). We found that the analog peptides exhibited higher stability and improved antibacterial activity compared with PMAP-23. Additionally, the analog peptides PMAP-23I and PMAP-23RI inhibited the growth of Shigella flexneri CICC 21534, whereas PMAP-23 and PMAP-23R exhibited no antibacterial activity against S. flexneri CICC 21534. Moreover, the peptide analogs showed negligible hemolysis and cytotoxicity. We also found that PMAP-23RI exerted impressive therapeutic effects on mice infected with Staphylococcus aureus ATCC 25923 and Salmonella enterica serovar Typhimurium SL1344. PMAP-23RI induced a greater reduction in pathological damage and a higher decrease in the bacterial gene copies in the lung and liver tissues and greatly reduced mouse mortality. In conclusion, the peptide analogs PMAP-23R, PMAP-23I, and PMAP-23RI enhanced the stability and antimicrobial activity of PMAP-23, but PMAP-23RI exhibits more promise as a new antimicrobial agent candidate for the treatment of bacterial infections.

Identification and recombinant expression of an antimicrobial peptide (cecropin B-like) from soybean pest Anticarsia gemmatalis

ABSTRACT

BACKGROUND

Insects can be found in numerous diverse environments, being exposed to pathogenic organisms like fungi and bacteria. Once these pathogens cross insect physical barriers, the innate immune system operates through cellular and humoral responses. Antimicrobial peptides are small molecules produced by immune signaling cascades that develop an important and generalist role in insect defenses against a variety of microorganisms. In the present work, a cecropin B-like peptide (AgCecropB) sequence was identified in the velvetbean caterpillar Anticarsia gemmatalis and cloned in a bacterial plasmid vector for further heterologous expression and antimicrobial tests.

METHODS

AgCecropB sequence (without the signal peptide) was cloned in the plasmid vector pET-M30-MBP and expressed in the Escherichia coli BL21(DE3) expression host. Expression was induced with IPTG and a recombinant peptide was purified using two affinity chromatography steps with Histrap column. The purified peptide was submitted to high-resolution mass spectrometry (HRMS) and structural analyses. Antimicrobial tests were performed using gram-positive (Bacillus thuringiensis) and gram-negative (Burkholderia kururiensis and E. coli) bacteria.

RESULTS

AgCecropB was expressed in E. coli BL21 (DE3) at 28°C with IPTG 0.5 mM. The recombinant peptide was purified and enriched after purification steps. HRMS confirmed AgCrecropB molecular mass (4.6 kDa) and circular dichroism assay showed α-helix structure in the presence of SDS. AgCrecropB inhibited almost 50% of gram-positive B. thuringiensis bacteria growth.

CONCLUSIONS

The first cecropin B-like peptide was described in A. gemmatalis and a recombinant peptide was expressed using a bacterial platform. Data confirmed tertiary structure as predicted for the cecropin peptide family. AgCecropB was capable to inhibit B. thuringiensis growth in vitro.

Enhancing the antibacterial activity of antimicrobial peptide PMAP-37(F34-R) by cholesterol modification

BACKGROUND

The problem of increasing resistance against conventional antibiotics has drawn people's attention. Therefore, the development of novel antibacterial agents with effective and safe therapeutic effects is imminent. Antimicrobial peptides (AMPs) are considered a promising class of antibacterial agents due to their broad antibacterial spectrum.

RESULTS

In this study, on the basis of our previously studied peptide PMAP-37(F34-R), a novel antimicrobial peptide Chol-37(F34-R) was developed by N-terminal cholesterol modification to increase hydrophobicity. We observed that the N-terminal cholesterol-modified Chol-37(F34-R) showed higher antimicrobial activity than PMAP-37(F34-R) in vitro. Chol-37(F34-R) also exhibited effective anti-biofilm activity and may kill bacteria by improving the permeability of their membranes. Chol-37(F34-R) exerted high stability in different pH, salt, serum, and boiling water environments. Chol-37(F34-R) also showed no hemolytic activity and substantially low toxicity. Furthermore, Chol-37(F34-R) exhibited good potency of bacteria eradication and promoted wound healing and abscess reduction in infected mice. Meanwhile, in S. aureus ATCC25923-infected peritonitis model, Chol-37(F34-R) exhibited an impressive therapeutic effect by reducing the decrease in systemic bacterial burden and alleviating organ damage.

CONCLUSIONS

Our findings suggested that the N-terminal cholesterol modification of PMAP-37(F34-R) could improve antibacterial activity. Chol-37(F34-R) displayed excellent bactericidal efficacy and impressive therapeutic effect in vivo. Thus, Chol-37(F34-R) may be a candidate for antimicrobial agents against microbial infection in the clinic.

Decanoic acid modification enhances the antibacterial activity of PMAP-23RI-Dec

Antimicrobial peptides are a new type of antibacterial drugs with a broad antibacterial spectrum. Based on our previous research, PMAP-23RI-Dec was designed by modifying the C-terminal of PMAP-23RI with decanoic acid. In this study, we measured the antibacterial activity, stability, hemolysis, and cytotoxicity of PMAP-23RI-Dec. The mechanism of PMAP-23RI-Dec on biofilm and cell membranes were also studied. The results show that PMAP-23RI-Dec exhibited high antibacterial activity and stability, but the hemolytic activity and cytotoxicity of PMAP-23RI-Dec were not enhanced. Moreover, PMAP-23RI-Dec could inhibit biofilm formation at low concentrations, and enhance the killing effect on bacteria by changing the permeability of their cell membranes. Finally, PMAP-23RI-Dec reduced Pseudomonas aeruginosa GIM1.551 and Staphylococcus aureus ATCC25923 damage to organs, and showed superior efficacy against peritonitis. PMAP-23RI-Dec also reduced the scope of abscess and alleviated wound infections. Our research indicated that PMAP-23RI-Dec is a new antibacterial agent with potential clinical application.

N-terminal Myristoylation Enhanced the Antimicrobial Activity of Antimicrobial Peptide PMAP-36PW

Drug-resistant bacteria infections and drug residues have been increasing and causing antibiotic resistance and public health threats worldwide. Antimicrobial peptides (AMPs) are novel antimicrobial drugs with the potential to solve these problems. Here, a peptide based on our previously studied peptide PMAP-36PW was designed via N-terminal myristoylation and referred to as Myr-36PW. The fatty acid modification provided the as-prepared peptide with good stability and higher antimicrobial activity compared with PMAP-36PW in vitro. Moreover, Myr-36PW exhibited effective anti-biofilm activity against Gram-negative bacteria and may kill bacteria by improving the permeability of their membranes. In addition, the designed peptide Myr-36PW could inhibit the bacterial growth of Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa GIM 1.551 to target organs, decrease the inflammatory damage, show an impressive therapeutic effect on mouse pneumonia and peritonitis experiments, and promote abscess reduction and wound healing in infected mice. These results reveal that Myr-36PW is a promising antimicrobial agent against bacterial infections.

Antimicrobial peptide PMAP-37 analogs: Increasing the positive charge to enhance the antibacterial activity of PMAP-37

Bacterial resistance induced by the use of antibiotics has provided a chance for the development of antimicrobial peptides (AMPs), and modification of AMPs to enhance the antibacterial activity or stability has become a research focus. PMAP-37 is an AMP isolated from porcine myeloid marrow, and studies on its modification have not yet been reported. In this study, three PMAP-37 analogs named PMAP-37(F9-R), PMAP-37(F34-R), and PMAP-37(F9/34-R) were designed by residue substitution to enhance the positive charge. The antimicrobial activity of PMAP-37 and its analogs in vitro and in vivo were detected. The results showed that compared with PMAP-37, PMAP-37(F9-R) and PMAP-37(F9/34-R) exhibited antibacterial activity against S. flexneri CICC21534. Although PMAP-37(F34-R) had no antibacterial activity against S. flexneri CICC21534, its minimal inhibitory concentrations (MICs) were significantly lower than those of PMAP-37 against most bacterial strains. Besides, all PMAP-37 analogs were pH stable, retaining stable antibacterial activity after treatment with solution from pH 2 to pH 8/9. In addition, the PMAP-37 analogs displayed increased thermal stability, and PMAP-37(F34-R) retained >60% antibacterial activity after boiling for 2 hours. Furthermore, the PMAP-37 analogs exhibited impressive therapeutic efficacy in bacterial infections by reducing bacterial burden and inflammatory damage in the lung and liver, resulting in a reduction in mortality. Notably, the therapeutic effect of PMAP-37(F34-R) was comparable to that of ceftiofur sodium, and even superior to antibiotics in L. monocytogenes CICC21533 infection model. In conclusion, the PMAP-37(F34-R) may be a candidate for the treatment of bacterial infections in the clinic.

Enhancing the antibacterial activity of PMAP-37 by increasing its hydrophobicity

With increasing resistance against conventional antibiotics, there is an urgent need to discover novel substances to replace antibiotics. This need provides an opportunity for the development of antimicrobial peptides (AMPs). To develop new AMPs with effective and safe therapeutic effects, two PMAP-37 analogs called PMAP-37(R13-I) and PMAP-37(K20/27-I) were designed to increase hydrophobicity. Antimicrobial susceptibility testing and animal infection models were used to assess their antibacterial activity. The results showed that the minimal inhibitory concentrations of PMAP-37(R13-I) were lower than those of PMAP-37 for two gram-negative strains. Compared with PMAP-37, PMAP-37(K20/27-I) not only inhibited the growth of most bacterial strains, but also exhibited antibacterial activity against Shigella flexneri CICC21534. In addition, PMAP-37(K20/27-I) exhibited pH and thermal stability. PMAP-37(R13-I) had a therapeutic effect only in mice infected with Salmonella typhimurium SL1344. However, PMAP-37(K20/27-I) exhibited the therapeutic effects, whether in the clinical symptoms, the tissue lesions, or the tissue bacterial loads and the survival rates in mice infected with Staphylococcus aureus ATCC25923 or S. typhimurium SL1344. Therefore, PMAP-37(K20/27-I) can be used as a substitute for antibiotics against infection with bacterial strains.