A recombinant fungal defensin-like peptide-P2 combats multidrug-resistant Staphylococcus aureus and biofilms

Expression and characterization of the new antimicrobial peptide AP138L-arg26 anti Staphylococcus aureus

The low activity and yield of antimicrobial peptides (AMPs) are pressing problems. The improvement of activity and yield through modification and heterologous expression, a potential way to solve the problem, is a research hot-pot. In this work, a new plectasin-derived variant L-type AP138 (AP138L-arg26) was constructed for the study of recombination expression and druggablity. As a result, the total protein concentration of AP138L-arg26 was 3.1 mg/mL in Pichia pastoris X-33 supernatant after 5 days of induction expression in a 5-L fermenter. The recombinant peptide AP138L-arg26 has potential antibacterial activity against selected standard and clinical Gram-positive bacteria (G+, minimum inhibitory concentration (MIC) 2-16 µg/mL) and high stability under different conditions (temperature, pH, ion concentration) and 2 × MIC of AP138L-arg26 could rapidly kill Staphylococcus aureus (S. aureus) (> 99.99%) within 1.5 h. It showed a high safety in vivo and in vivo and a long post-antibiotic effect (PAE, 1.91 h) compared with vancomycin (1.2 h). Furthermore, the bactericidal mechanism was revealed from two dimensions related to its disruption of the cell membrane resulting in intracellular potassium leakage (2.5-fold higher than control), and an increase in intracellular adenosine triphosphate (ATP), and reactive oxygen species (ROS), the decrease of lactate dehydrogenase (LDH) and further intervening metabolism in S. aureus. These results indicate that AP138L-arg26 as a new peptide candidate could be used for more in-depth development in the future. KEY POINTS: • The AP138L-arg26 was expressed in the P. pastoris expression system with high yield • The AP138 L-arg26 showed high stability and safety in vitro and in vivo • The AP138L-arg26 killed S. aureus by affecting cell membranes and metabolism.

Antibiofilm Efficacy and Mechanism of the Marine Chlorinated Indole Sesquiterpene Against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) can easily form biofilms on food surfaces, thus leading to cross-contamination, which is difficult to remove. Therefore, there is an urgent need to find alternatives with good antibacterial and antibiofilm effects. In this study, two indole sesquiterpene compounds, xiamycin (1) and chlorinated metabolite chloroxiamycin (2), were isolated from the fermentation liquid of marine Streptomyces sp. NBU3429 for the first time. The chemical structures of the two compounds were characterized by spectroscopic data interpretation, including 1D NMR and HRESIMS analysis. Antimicrobial test showed that chloroxiamycin (2) (minimum inhibitory concentration, MIC = 16 μg/mL) exhibited superior antibacterial activity than xiamycin (1) (MIC = 32 μg/mL) against MRSA ATCC43300. Moreover, compound (2) decreased the biofilm formation rate of MRSA ATCC43300 by 12.7%-84.6% in the concentration range of 32-512 μg/mL, which is relatively stronger than xiamycin (1) (4.1%-49.9%) as well. Antibacterial/antibiofilm mechanism investigation indicated that chloroxiamycin (2) could disrupt the cell wall and membrane of MRSA, inhibiting the production of biofilm extracellular polysaccharides. All these results illustrated that chloroxiamycin (2) is an effective antibacterial/antibiofilm agent, which makes it an attractive candidate for food preservatives.

Expression, Purification and Biophysical Characterisation of Klebsiella Pneumoniae Protein Adenylyltransferase: A Systematic Integration of Empirical and Computational Modelling Approaches

Infections that are acquired due to a prolonged hospital stay and manifest 2 days following the admission of a patient to a health-care institution can be classified as hospital-acquired infections. Klebsiella pneumoniae (K. pneumoniae) has become a critical pathogen, posing serious concern globally due to the rising incidences of hypervirulent and carbapenem-resistant strains. Glutaredoxin is a redox protein that protects cells from oxidative stress as it associates with glutathione to reduce mixed disulfides. Protein adenylyltransferase (PrAT) is a pseudokinase with a proposed mechanism of transferring an AMP group from ATP to glutaredoxin. Inducing oxidative stress to the bacterium by inhibiting the activity of PrAT is a promising approach to combating its contribution to hospital-acquired infections. Thus, this study aims to overexpress, purify, and analyse the effects of ATP and Mg2+ binding to Klebsiella pneumoniae PrAT (KpPrAT). The pET expression system and nickel affinity chromatography were effective in expressing and purifying KpPrAT. Far-UV CD spectroscopy demonstrates that the protein is predominantly α-helical, even in the presence of Mg2+. Extrinsic fluorescence spectroscopy with ANS indicates the presence of a hydrophobic pocket in the presence of ATP and Mg2+, while mant-ATP studies allude to the potential nucleotide binding ability of KpPrAT. The presence of Mg2+ increases the thermostability of the protein. Isothermal titration calorimetry provides insight into the binding affinity and thermodynamic parameters associated with the binding of ATP to KpPrAT, with or without Mg2+. Conclusively, the presence of Mg2+ induces a conformation in KpPrAT that favours nucleotide binding.

Multifunctional Drug- and AuNRs-Loaded ROS-Responsive Selenium-Containing Polyurethane Nanofibers for Smart Wound Healing

Elevated levels of ROS, bacterial infection, inflammation, and improper regeneration are the factors that need to be addressed simultaneously for achieving effective wound healing without scar formation. This study focuses on the fabrication of electrospun ROS-responsive selenium-containing polyurethane nanofibers incorporating deferoxamine mesylate (Def), indomethacin (Indo), and gold nanorods (AuNRs) as proangiogenesis, anti-inflammatory, and antibacterial agents for synchronized delivery to a full-thickness wound in vivo. The structure of the fabricated nanofibers was analyzed by various techniques. Toxicity was checked by CCK-8 and hemolytic assays. The efficiency of wound healing in vitro was verified by a transwell assay and cell scratch assay. The wound healing efficiency of the nanofibers was assayed in full-thickness wounds in a rat model. The multifunctional nanofibers had a porous structure, enhanced antioxidation, antibacterial activity, and promoted wound healing. They eradicated TNF-α and IL-6, increased IL-10 expression, and revealed the angiogenic potential by increased expression of HIF-1α, VEGF, and CD31.

Characterization of a novel circular bacteriocin from Bacillus velezensis 1-3, and its mode of action against Listeria monocytogenes

In this study, isolate Bacillus velezensis1-3 was selected out for its anti- Listeria potency, from which a novel circular bacteriocin, velezin, was purified out of the fermentate, and then characterized. Facilitated with a broad antibacterial spectrum, velezin has demonstrated decent inhibitive activity against of foodborne pathogen L. monocytogenes ATCC 19115. It exerted the antibacterial activity through damaging the membrane integrity of targeted cell and causing leakage of vital elements, including K+ ion. It was noteworthy that velezin also inhibited the biofilm formation by L. monocytogenes ATCC 19115. At the challenge of velezin, L. monocytogenes ATCC 19115 up-regulated expression of genes associated with membrane, ion transporters, stressing-related proteins as well as the genes responsible for the synthesis of small molecule. Taken together, velezin may have potential to be a candidate as natural additive used in food/feed in the future.

Design of a Novel Lysine Isopeptide 1018KI11 with Potent Antimicrobial Activity as a Safe and Stable Food Preservative Candidate

Antimicrobial peptides are potent food additive candidates, but most of them are sensitive to proteases, which limits their application. Therefore, we substituted arginine for lysine and introduced a lysine isopeptide bond to peptide IDR-1018 in order to improve its enzymatic stability. Subsequently, the protease stability and antimicrobial/antibiofilm activity of the novel peptides (1018K2-1018KI11) were investigated. The data revealed that the antienzymatic potential of 1018KI11 to bromelain and papain increased by 2-8 folds and 16 folds, respectively. The minimum inhibitory concentration (MIC) of 1018KI11 against methicillin-resistant Staphylococcus aureus (MRSA) ATCC43300 and Escherichia coli (E. coli) ATCC25922 was reduced 2-fold compared to 1018K11. Mechanism exploration suggested that 1018KI11 was more effective than 1018K11 in disrupting the cell barrier and damaging genomic DNA. Additionally, 1018KI11 at certain concentration conditions (2-64 μg/mL) reduced biofilm development of MRSA ATCC43300 by 4.9-85.9%. These data indicated that novel peptide 1018KI11 is a potential food preservative candidate.

Pharmacokinetics and pharmacodynamics of antibacterial peptide NZX in Staphylococcus aureus mastitis mouse model

Staphylococcus aureus is associated with dairy mastitis, which causes serious economic losses to dairy farming industry. Antibacterial peptide NZX showed good antibacterial activity against S. aureus. This study aimed to evaluate pharmacokinetics and pharmacodynamics of NZX against S. aureus-induced mouse mastitis. NZX exhibited potent in vitro antibacterial activity against the test S. aureus strains (minimal inhibitory concentration (MIC): 0.23-0.46 μM), low mutant prevention concentration (MPC: 1.18-3.68 μM), and a long post antibiotic effect (PAE: 2.20-8.84 h), which was superior to those of lincomycin and ceftiofur. Antibacterial mechanisms showed that NZX could penetrate the cell membrane, resulting in obvious cell membrane perforation and morphological changes, and bind to intracellular DNA. Furthermore, NZX had a good stability in milk environment (retention rate: 85.36%, 24 h) than that in mammary homogenate (47.90%, 24 h). In mouse mastitis model, NZX (25-400 μg/gland) could significantly reduce the bacterial load of mammary tissue in a dose-dependent manner. In addition, NZX (100 μg/gland) could relieve the inflammatory symptoms of mammary tissue, and significantly decreased its pathological scores. The concentration-time curve of NZX (100 μg/gland) in the mammary tissue was plotted and the corresponding pharmacokinetic parameters were obtained by non-compartment model calculation. Those parameters of Tmax, T1/2, Cmax and AUC were 0.5 h, 35.11 h, 32.49 μg/g and 391 μg·h/g, respectively. Therefore, these results suggest that NZX could act as a promising candidate for treating dairy mastitis disease caused by S. aureus. KEY POINTS: • NZX could kill S. aureus by dual mechanism involved in membrane and DNA disruption • NZX could relieve S. aureus-induced mouse mastitis • Pharmacokinetic parameters of NZX in mouse mammary gland were obtained.

Anti-Staphylococcus aureus effects of natural antimicrobial peptides and the underlying mechanisms

Staphylococcus aureus can cause localized infections such as abscesses and pneumonia, as well as systemic infections such as bacteremia and sepsis. Especially, methicillin-resistant S. aureus often presents multidrug resistance, which becomes a major clinical challenge. One of the most common reasons for methicillin-resistant S. aureus antibiotic resistance is the presence of biofilms. Natural antimicrobial peptides derived from different species have shown effectiveness in combating S. aureus biofilms. In this review, we summarize the inhibitory activity of antimicrobial peptides against S. aureus planktonic cells and biofilms. We also summarize the possible inhibitory mechanisms, involving cell adhesion inhibition, membrane fracture, biofilm disruption and DNA disruption. We believe this can provide the basis for further research against S. aureus biofilm-associated infections.

Polylactic Glycolic Acid-Mediated Delivery of Plectasin Derivative NZ2114 in Staphylococcus epidermidis Biofilms

Antimicrobial peptides (AMPs) are antibiotic candidates; however, their instability and protease susceptibility limit clinical applications. In this study, the polylactic acid-glycolic acid (PLGA)-polyvinyl alcohol (PVA) drug delivery system was screened by orthogonal design using the double emulsion-solvent evaporation method. NZ2114 nanoparticles (NZ2114-NPs) displayed favorable physicochemical properties with a particle size of 178.11 ± 5.23 nm, polydispersity index (PDI) of 0.108 ± 0.10, ζ potential of 4.78 ± 0.67 mV, actual drug-loading rate of 4.07 ± 0.37%, encapsulation rate of 81.46 ± 7.42% and cumulative release rate of 67.75% (120 h) in PBS. The results showed that PLGA encapsulation increased HaCaT cell viability by 20%, peptide retention in 50% serum by 24.12%, and trypsin tolerance by 4.24-fold. Meanwhile, in vitro antimicrobial assays showed that NZ2114-NPs had high inhibitory activity against Staphylococcus epidermidis (S. epidermidis) (4-8 μg/mL). Colony counting and confocal laser scanning microscopy (CLSM) confirmed that NZ2114-NPs were effective in reducing the biofilm thickness and bacterial population of S. epidermidis G4 with a 99% bactericidal rate of persister bacteria, which was significantly better than that of free NZ2114. In conclusion, the results demonstrated that PLGA nanoparticles can be used as a reliable NZ2114 delivery system for the treatment of biofilm infections caused by S. epidermidis.

Plectasin: from evolution to truncation, expression, and better druggability

Non-computational classical evolution analysis of plectasin and its functional relatives can especially contribute tool value during access to meet requirements for their better druggability in clinical use. Staphylococcus aureus is a zoonotic pathogen that can infect the skin, blood, and other tissues of humans and animals. The impact of pathogens on humans is exacerbated by the crisis of drug resistance caused by the misuse of antibiotics. In this study, we analyzed the evolution of anti-Staphylococcus target functional sequences, designed a series of plectasin derivatives by truncation, and recombinantly expressed them in Pichia pastoris X-33, from which the best recombinant Ple-AB was selected for the druggability study. The amount of total protein reached 2.9 g/L following 120 h of high-density expression in a 5-L fermenter. Ple-AB was found to have good bactericidal activity against gram-positive bacteria, with minimum inhibitory concentration (MIC) values ranging between 2 and 16 μg/mL. It showed good stability and maintained its bactericidal activity during high temperatures, strong acid and alkali environments. Notably, Ple-AB exhibited better druggability, including excellent trypsin resistance, and still possessed approximately 50% of its initial activity following exposure to simulated intestinal fluids for 1 h. In vitro safety testing of Ple-AB revealed low hemolytic activity against mouse erythrocytes and cytotoxicity against murine-derived macrophages. This study successfully realized the high expression of a new antimicrobial peptide (AMP), Ple-AB, in P. pastoris and the establishment of its oral administration as an additive form with high trypsin resistance; the study also revealed its antibacterial properties, indicating that truncation design is a valuable tool for improving druggability and that the candidate Ple-AB may be a novel promising antimicrobial agent.

High-Yield Preparation of American Oyster Defensin (AOD) via a Small and Acidic Fusion Tag and Its Functional Characterization

The marine peptide, American oyster defensin (AOD), is derived from Crassostrea virginica and exhibits a potent bactericidal effect. However, recombinant preparation has not been achieved due to the high charge and hydrophobicity. Although the traditional fusion tags such as Trx and SUMO shield the effects of target peptides on the host, their large molecular weight (12-20 kDa) leads to the yields lower than 20% of the fusion protein. In this study, a short and acidic fusion tag was employed with a compact structure of only 1 kDa. Following 72 h of induction in a 5 L fermenter, the supernatant exhibited a total protein concentration of 587 mg/L. The recombinant AOD was subsequently purified through affinity chromatography and enterokinase cleavage, resulting in the final yield of 216 mg/L and a purity exceeding 93%. The minimum inhibitory concentrations (MICs) of AOD against Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus galactis ranged from 4 to 8 μg/mL. Moreover, time-killing curves indicated that AOD achieved a bactericidal rate of 99.9% against the clinical strain S. epidermidis G-81 within 0.5 h at concentrations of 2× and 4× MIC. Additionally, the activity of AOD was unchanged after treatment with artificial gastric fluid and intestinal fluid for 4 h. Biocompatibility testing demonstrated that AOD, at a concentration of 128 μg/mL, exhibited a hemolysis rate of less than 0.5% and a cell survival rate of over 83%. Furthermore, AOD's in vivo therapeutic efficacy against mouse subcutaneous abscess revealed its capability to restrain bacterial proliferation and reduce bacterial load, surpassing that of antibiotic lincomycin. These findings indicate AOD's potential for clinical usage.

A cleavable chimeric peptide with targeting and killing domains enhances LPS neutralization and antibacterial properties against multi-drug resistant E. coli

Pathogenic Escherichia coli is one of the most common causes of diarrhea diseases and its characteristic component of the outer membrane-lipopolysaccharide (LPS) is a major inducer of sepsis. Few drugs have been proven to kill bacteria and simultaneously neutralize LPS toxicity. Here, the chimeric peptides-R7, A7 and G7 were generated by connecting LBP14 (LPS-targeting domain) with L7 (killing domain) via different linkers to improve antibacterial and anti-inflammatory activities. Compared to parent LBP14-RKRR and L7, the antibacterial activity of R7 with a cleavable "RKRR" linker and the "LBP14-RKRR + L7" cocktail against Escherichia coli, Salmonella typhimurium and Staphylococcus aureus was increased by 2 ~ 4-fold. Both A7 and G7 with non-cleavable linkers almost lost antibacterial activity. The ability of R7 to neutralize LPS was markedly higher than that of LBP14-RKRR and L7. In vivo, R7 could be cleaved by furin in a time-dependent manner, and release L7 and LBP14-RKRR in serum. In vivo, R7 can enhance mouse survival more effectively than L7 and alleviate lung injuries by selective inhibition of the NF-κB signaling pathways and promoting higher IAP activity. It suggests that R7 may be promising dual-function candidates as antibacterial and anti-endotoxin agents.

Killing of Staphylococcus aureus persisters by a multitarget natural product chrysomycin A

Staphylococcus aureus poses a severe public health problem as one of the vital causative agents of healthcare- and community-acquired infections. There is a globally urgent need for new drugs with a novel mode of action (MoA) to combat S. aureus biofilms and persisters that tolerate antibiotic treatment. We demonstrate that a benzonaphthopyranone glycoside, chrysomycin A (ChryA), is a rapid bactericide that is highly active against S. aureus persisters, robustly eradicates biofilms in vitro, and shows a sustainable killing efficacy in vivo. ChryA was suggested to target multiple critical cellular processes. A wide range of genetic and biochemical approaches showed that ChryA directly binds to GlmU and DapD, involved in the biosynthetic pathways for the cell wall peptidoglycan and lysine precursors, respectively, and inhibits the acetyltransferase activities by competition with their mutual substrate acetyl-CoA. Our study provides an effective antimicrobial strategy combining multiple MoAs onto a single small molecule for treatments of S. aureus persistent infections.

Site Mutation Improves the Expression and Antimicrobial Properties of Fungal Defense

Although antimicrobial peptides (AMPs) have highly desirable intrinsic characteristics in their commercial product development as new antimicrobials, the limitations of AMPs from experimental to scale development include the low oral bioavailability, and high production costs due to inadequate in vitro/in vivo gene expression- and low scale. Plectasin has good bactericidal activity against Staphylococcus and Streptococcus, and the selective bactericidal activity greatly reduces the damage to the micro-ecosystem when applied in vivo. However, its expression level was relatively low (748.63 mg/L). In view of these situations, this study will optimize and modify the structure of Plectasin, hoping to obtain candidates with high expression, no/low toxicity, and maintain desirable antibacterial activity. Through sequence alignment, Plectasin was used as a template to introduce the degenerate bases, and the screening library was constructed. After three different levels of screening, the candidate sequence PN7 was obtained, and its total protein yield in the supernatant was 5.53 g/L, with the highest value so far for the variants or constructs from the same ancestor source. PN7 had strong activity against several species of Gram-positive bacteria (MIC value range 1~16 μg/mL). It was relatively stable in various conditions in vitro; in addition, the peptide showed no toxicity to mice for 1 week after intraperitoneal injection. Meanwhile, PN7 kills Staphylococcus aureus ATCC 43300 with a mode of a quicker (>99% S. aureus was killed within 2 h, whereas vancomycin at 2× MIC was 8 h.) and longer PAE period. The findings indicate that PN7 may be a novel promising antimicrobial agent, and this study also provides a model or an example for the design, modification, or reconstruction of novel AMPs and their derivatives.

D- and N-Methyl Amino Acids for Modulating the Therapeutic Properties of Antimicrobial Peptides and Lipopeptides

Here we designed and synthesized analogs of two antimicrobial peptides, namely C10:0-A2, a lipopeptide, and TA4, a cationic α-helical amphipathic peptide, and used non-proteinogenic amino acids to improve their therapeutic properties. The physicochemical properties of these analogs were analyzed, including their retention time, hydrophobicity, and critical micelle concentration, as well as their antimicrobial activity against gram-positive and gram-negative bacteria and yeast. Our results showed that substitution with D- and N-methyl amino acids could be a useful strategy to modulate the therapeutic properties of antimicrobial peptides and lipopeptides, including enhancing stability against enzymatic degradation. The study provides insights into the design and optimization of antimicrobial peptides to achieve improved stability and therapeutic efficacy. TA4(dK), C10:0-A2(6-NMeLys), and C10:0-A2(9-NMeLys) were identified as the most promising molecules for further studies.

Molecular Modification of Kex2 P1' Site Enhances Expression and Druggability of Fungal Defensin

Pichia pastoris is the widely used expression system for producing recombinant secretory proteins. It is known that Kex2 protease plays a vital role in the process of protein secretion, in which the P1' site affects its cleavage efficiency. To enhance the expression level of fungal defensin-derived peptide NZ2114, this work attempts to optimize the P1' site of Kex2 by replacing it with 20 amino acids in turn. The results showed that when the amino acid of the P1' site was changed to Phe (F), the yield of target peptide significantly increased from 2.39 g/L to 4.81 g/L. Additionally, the novel peptide F-NZ2114 (short for FNZ) showed strong antimicrobial activity against Gram-positive (G⁺) bacteria, especially for Staphylococcus aureus and Streptococcus agalactiae (MIC: 4-8 μg/mL). The FNZ was very stable and retained high activity in various conditions; in addition, a low cytotoxicity and no hemolysis were observed even at a high concentration of 128 μg/mL, and a longer postantibiotic effect was reached. The above results indicate that this engineering strategy provided a feasible optimization scheme for enhancing the expression level and druggability of this antimicrobial peptide from fungal defensin and other similar targets by this updated recombinant yeast.

Thinking on the Construction of Antimicrobial Peptide Databases: Powerful Tools for the Molecular Design and Screening

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.

The future of recombinant host defense peptides

The antimicrobial resistance crisis calls for the discovery and production of new antimicrobials. Host defense peptides (HDPs) are small proteins with potent antibacterial and immunomodulatory activities that are attractive for translational applications, with several already under clinical trials. Traditionally, antimicrobial peptides have been produced by chemical synthesis, which is expensive and requires the use of toxic reagents, hindering the large-scale development of HDPs. Alternatively, HDPs can be produced recombinantly to overcome these limitations. Their antimicrobial nature, however, can make them toxic to the hosts of recombinant production. In this review we explore the different strategies that are used to fine-tune their activities, bioengineer them, and optimize the recombinant production of HDPs in various cell factories.

D1018 with higher stability and excellent lipopolysaccharide binding affinity has potent anti-bacterial and anti-inflammatory activity

Escherichia coli (E. coli) infection and LPS-induced inflammation are still of severe threat to human health. With the increasing problem of antibiotic resistance, there is a desperate need to develop new approaches to solve the problem. Antimicrobial peptide (AMP) IDR-1018 exhibited potential antimicrobial and immunoregulation activity. However, moderate antimicrobial efficiency and susceptibility to protease cleavage limited its therapeutic application. Therefore, the derived 1018M which has better activity against MRSA and whole sequence D-amino acids substitution peptides (D1018 and D1018M) were synthesized in this study. The resistance of D1018 and D1018M against tested proteases increased (2–4 times), particularly in D1018. The antibacterial activity of D1018 was the same as that of the parent peptide IDR-1018, but the antimicrobial activity of D1018M was slightly increased (2-fold). Though the hemolysis of IDR-1018 and D1018 was about 2%, at the concentration of 8×MIC, the cytotoxicity of IDR-1018, D1018, and 1018M was negligible. The peptides could interact with E. coli cell wall and cytoplasmic membrane, penetrate the membrane, cause leakage of contents, and disrupt genomic DNA. Among them, D1018 is the most prominent one. In addition, IDR-1018 and D1018 showed potent binding ability to LPS, thus leading to excellent inhibition capacity to LPS-induced proinflammation response. Taken together, these data demonstrate that D1018 is a promising peptide candidate for the treatment of E. coli infection.

Effect of NZ2114 against Streptococcus dysgalactiae biofilms and its application in murine mastitis model

Bovine mastitis caused by Streptococcus dysgalactiae (S. dysgalactiae) is usually treated with antibiotics, which may potentially increase drug resistance as the abuse. NZ2114, a variant of fungal defensin plectasin, displayed a potent antibacterial activity against S. dysgalactiae. The inhibition/eradication effect of the antimicrobial peptide NZ2114 on the early/mature biofilm of S. dysgalactiae CVCC 3938 was evaluated, as well as the elimination of bacteria in mature biofilms. In this study, NZ2114 displayed potent antibacterial activity against S. dysgalactiae CVCC 3938 and three clinical isolated S. dysgalactiae strains (0.11-0.45 μM). The early biofilm inhibition of S. dysgalactiae CVCC 3938 was 55.5–85.9% after treatment with NZ2114 at concentrations of 1–16 × MIC, which was better than that of vancomycin at the same concentration. The mature biofilm eradication rate was up to 92.7–97.6% with the increasing concentration (2–16 × MIC) of NZ2114, and the eradication rate did not change significantly with further increase of NZ2114 concentration, while the biofilm eradication rate of vancomycin-treated group at the same concentration remained at 92.5%. NZ2114 reduced the number of persister bacteria in biofilm. Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) further demonstrated that NZ2114 could effectively reduce the biofilm thickness and bacterial number of S. dysgalactiae CVCC 3938. In vivo therapeutic effect of NZ2114 on murine mastitis model showed that NZ2114 was better than vancomycin in alleviating mammary gland inflammation by regulating cytokines production, inhibiting bacterial proliferation, and reducing the number of mammary gland bacteria. These data suggested that NZ2114 is a potential peptide candidate for the treatment of mastitis.

Membrane Permeabilization and Antimicrobial Activity of Recombinant Defensin-d2 and Actifensin against Multidrug-Resistant Pseudomonas aeruginosa and Candida albicans

Antimicrobial resistance requires urgent efforts towards the discovery of active antimicrobials, and the development of strategies to sustainably produce them. Defensin and defensin-like antimicrobial peptides (AMPs) are increasingly gaining pharmacological interest because of their potency against pathogens. In this study, we expressed two AMPs: defensin-d2 derived from spinach, and defensin-like actifensin from Actinomyces ruminicola. Recombinant pTXB1 plasmids carrying the target genes encoding defensin-d2 and actifensin were generated by the MEGAWHOP cloning strategy. Each AMP was first expressed as a fusion protein in Escherichia coli, purified by affinity chromatography, and was thereafter assayed for antimicrobial activity against multidrug-resistant (MDR) pathogens. Approximately 985 µg/mL and 2895 µg/mL of recombinant defensin-d2 and actifensin, respectively, were recovered with high purity. An analysis by MALDI-TOF MS showed distinct peaks corresponding to molecular weights of approximately 4.1 kDa for actifensin and 5.8 kDa for defensin-d2. An in vitro antimicrobial assay showed that MDR Pseudomonas aeruginosa and Candida albicans were inhibited at minimum concentrations of 7.5 µg/mL and 23 µg/mL for recombinant defensin-d2 and actifensin, respectively. The inhibitory kinetics of the peptides revealed cidal activity within 4 h of the contact time. Furthermore, both peptides exhibited an antagonistic interaction, which could be attributed to their affinities for similar ligands, as deduced by peptide–ligand profiling. Moreover, both peptides inhibited biofilm formation, and they exhibited no resistance potential and low hemolytic activity. The peptides also possess the ability to permeate and disrupt the cell membranes of MDR P. aeruginosa and C. albicans. Therefore, recombinant actifensin and defensin-d2 exhibit broad-spectrum antimicrobial activity and have the potential to be used as therapy against MDR pathogens.

Pharmacokinetics and Pharmacodynamics of Fungal Defensin NZX Against Staphylococcus aureus-Induced Mouse Peritonitis Model

Staphylococcus aureus (S. aureus) is one of the most common pathogenic bacteria responsible for causing a life-threatening peritonitis disease. NZX, as a variant of fungal defensin plectasin, displayed potent antibacterial activity against S. aureus. In this study, the antibacterial and resistance characteristics, pharmacokinetics, and pharmacodynamics of NZX against the S. aureus E48 and S. aureus E48-induced mouse peritonitis model were studied, respectively. NZX exhibited a more rapid killing activity to S. aureus (minimal inhibitory concentration, 1 μg/ml) compared with linezolid, ampicillin and daptomycin, and serial passaging of S. aureus E48 for 30 days at 1/2 × MIC, NZX had a lower risk of resistance compared with ampicillin and daptomycin. Also, it displayed a high biocompatibility and tolerance to physiological salt, serum environment, and phagolysosome proteinase environment, except for acid environment in phagolysosome. The murine serum protein-binding rate of NZX was 89.25% measured by ultrafiltration method. Based on the free NZX concentration in serum after tail vein administration, the main pharmacokinetic parameters for T_1/2, C_max, V_d, MRT, and AUC ranged from 0.32 to 0.45 h, 2.85 to 20.55 μg/ml, 1469.10 to 2073.90 ml/kg, 0.32 to 0.56 h, and 1.11 to 8.89 μg.h/ml, respectively. Additionally, the in vivo pharmacodynamics against S. aureus demonstrated that NZX administrated two times by tail vein at 20 mg/kg could rescue all infected mice in the lethal mouse peritonitis model. And NZX treatment (20 mg/kg) significantly reduced CFU counts in the liver, lung, and spleen, especially for intracellular bacteria in the peritoneal fluid, which were similar or superior to those of daptomycin. In vivo efficacies of NZX against total bacteria and intracellular bacteria were significantly correlated with three PK/PD indices of ƒAUC/MIC, ƒC_max/MIC, and ƒT% > MIC analyzed by a sigmoid maximum-effect model. These results showed that NZX may be a potential candidate for treating peritonitis disease caused by intracellular S. aureus.

C-terminal mini-PEGylation of a marine peptide N6 had potent antibacterial and anti-inflammatory properties against Escherichia coli and Salmonella strains in vitro and in vivo

Background

Enteropathogenic Escherichia coli and Salmonella pullorum are two important groups of zoonotic pathogens. At present, the treatment of intestinal pathogenic bacteria infection mainly relies on antibiotics, which directly inhibit or kill the pathogenic bacteria. However, due to long-term irrational, excessive use or abuse, bacteria have developed different degrees of drug resistance. N6, an arenicin-3 derivative isolated from the lugworm, has potent antibacterial activity and is poorly resistant to enzymatic hydrolysis and distribution in vivo. Polyethylene glycol (PEG) is an extensively studied polymer and commonly used in protein or peptide drugs to improve their therapeutic potential. Here, we modified the N-/C-terminal or Cys residue of N6 with liner PEGn of different lengths (n = 2, 6,12, and 24), and the effects of PEGylation of N6 on the stability, toxicity, bactericidal mechanism, distribution and efficacy were investigated in vitro and in vivo.

Results

The antimicrobial activity of the peptide showed that PEGylated N6 at the C-terminus (n = 2, N6-COOH-miniPEG) had potent activity against Gram-negative bacteria; PEGylated N6 at the N-terminus and Cys residues showed low or no activity with increasing lengths of PEG. N6-COOH-miniPEG has higher stability in trypsin than the parent peptide-N6. N6-COOH-miniPEG significantly regulated cytokine expression in lipopolysaccharides (LPS)-induced RAW 264.7 cells, and the levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-1β were reduced by 31.21%, 65.62% and 44.12%, respectively, lower than those of N6 (-0.06%, -12.36% and -12.73%); N6-COOH-miniPEG increased the level of IL-10 (37.83%), higher than N6 (-10.21%). The data indicated that N6-COOH-miniPEG has more potent anti-inflammatory and immune-regulatory effect than N6 in LPS-stimulated RAW 264.7 cells. N6-COOH-miniPEG exhibited a much wider biodistribution in mice and prolonged in vivo half-time. FITC-labeled N6-COOH-miniPEG was distributed throughout the body of mice in the range of 0.75 – 2 h after injection, while FITC-labeled N6 only concentrated in the abdominal cavity of mice after injection, and the distribution range was narrow. N6-COOH-miniPEG improved the survival rates of mice challenged with E. coli or S. pullorum, downregulated the levels of TNF-α, IL-6, IL-1β and IL-10 in the serum of LPS-infected mice, and alleviated multiple-organ injuries (the liver, spleen, kidney, and lung), superior to antibiotics, but slightly inferior to N6.

Conclusions

The antibacterial activity, bactericidal mechanism and cytotoxicity of N6-COOH-miniPEG and N6 were similar. N6-COOH-miniPEG has a higher resistance to trysin than N6. The distribution of N6-COOH-miniPEG in mice was superior to that of N6. In exploring the modulatory effects of antimicrobial peptides on cytokines, N6-COOH-miniPEG had stronger anti-inflammatory and immunomodulatory effects than N6. The results suggested that C-terminal PEGylated N6 may provide an opportunity for the development of effective anti-inflammatory and antibacterial peptides.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02534-w.

In Vitro Pharmacodynamics and Bactericidal Mechanism of Fungal Defensin-Derived Peptides NZX and P2 against Streptococcus agalactiae

(1) Background: Based on the hazard of Streptococcus agalactiae to human and animal health and the increasing drug resistance, it is urgent to develop new antimicrobial agents with high bactericidal activity and low drug resistance against S. agalactiae. This study aims to investigate in vitro pharmacodynamics and bactericidal mechanism of fungal defensin-derived peptides NZX and P2 against S. agalactiae. (2) Methods: Minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) were determined by broth dilution method and AGAR plate dilution method. Cell membrane integrity was determined by flow cytometer. Cell morphological changes were observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). (3) Results: MIC values (NZX: 0.11 μM, P2: 0.91 μM) and MPC (NZX: 1.82 μM) showed their higher antibacterial activity and stronger inhibition ability of drug resistance mutation. The bactericidal mechanism was elucidated that P2 caused S. agalactiae ACCC 61733 cells to deform, bound to the cell wall, and perturbed cell membrane, resulting in K⁺ leakage, membrane hyperpolarization, ATP release, and reduced cell contents. Compared with P2, NZX focuses on the cell wall, and it bound to the cell wall causing cells boundary disappearance. (4) Conclusion: NZX and P2 are promising antimicrobial agents for streptococcicosis treatment.

Anti-persister strategies against stress induced bacterial persistence

The increase in antibiotic non-responsive bacteria is the leading concern in current research-oriented to eliminate pathogens. Nowadays, the excess use of antibiotics without specifically understanding the potentiality of killing pathogens and bacterial survival patterns has helped bacteria emerge indefatigably. Bacteria use various mechanisms such as resistance, persistence, and tolerance to ensure survival. Among these, persistence is a mechanism by which bacteria reside in their dormant state, bypassing the effects of treatments, making it crucial for bacterial survival. Persistent bacterial cells arise from the normal bacterial population as a slow-growing subset of bacteria with no metabolic flux. This behavior renders it to survive for a longer duration and at higher concentrations of antibiotics. They are one of the underlying causes of recurrence of bacterial infections. The present article explains the detailed molecular mechanisms and strategies of bacterial persistence, including the toxin-antitoxin modules, DNA damage, the formation of inactive ribosomal complexes, (p)ppGpp network, antibiotic-induced persistence, which are triggered by drug-induced stress. The article also comprehensively covers the epigenetic memory of persistence in bacteria, and anti-persistent therapeutics like antimicrobial molecules, synthetic peptides, acyldepsipeptide antibiotics, and endolysin therapy to reduce persister cell formation and control their frequency. These strategies could be utilized in combating the pathogenic bacteria undergoing persistence.

Fascaplysin derivatives binding to DNA via unique cationic five-ring coplanar backbone showed potent antimicrobial/antibiofilm activity against MRSA in vitro and in vivo

Methicillin-resistant Staphylococcus aureus (MRSA) is considered as one of the most dangerous clinical pathogens. Biofilms forming ability of MRSA is also a major cause of drug resistance. Hence, it is in urgent need to develop novel antibacterial/antibiofilm drugs. Fascaplysin with a unique cationic five-ring coplanar backbone is emerging as a potential antibacterial compound. In this study, aiming at developing novel and more effective agents, a series of fascaplysin derivatives and their corresponding β-carboline precursors have been synthesized. Then their antibacterial/antibiofilm activity and mechanisms against MRSA were investigated for the first time. The results showed that most fascaplysins rather than β-carboline precursors exhibit superior antimicrobial activity against MRSA ATCC43300, demonstrating the important role of cationic five-ring coplanar backbone playing in antibacterial activity. Among them, 14 and 18 are the most potent compounds with MIC value of 0.098 μg/ml (10-fold lower than vancomycin), and 18 featuring the lowest toxicity. Subsequent mechanisms exploration indicates that 18 has relatively stronger ability to destroy bacterial cell wall and membrane, higher binding affinity to bacterial genomic DNA. Molecular docking study revealed that besides the key role of cationic five-ring coplanar backbone, introduction of N-aryl amide at 9-position of fascaplysin promoted the combination of compound 18 and DNA via additional π-π stacking and hydrogen bonding of the naphthyl group. Moreover, fascaplysins could inhibit MRSA biofilm formation in vitro and bacterial infection in vivo. All these results illustrate that fascaplysin derivative 18 is a strong and safe multi-target antibacterial agent, which makes it an attractive candidate for the treatment of MRSA and its biofilm infections.

New Perspectives on Old and New Therapies of Staphylococcal Skin Infections: The Role of Biofilm Targeting in Wound Healing

Among the most common complications of both chronic wound and surgical sites are staphylococcal skin infections, which slow down the wound healing process due to various virulence factors, including the ability to produce biofilms. Furthermore, staphylococcal skin infections are often caused by methicillin-resistant Staphylococcus aureus (MRSA) and become a therapeutic challenge. The aim of this narrative review is to collect the latest evidence on old and new anti-staphylococcal therapies, assessing their anti-biofilm properties and their effect on skin wound healing. We considered antibiotics, quorum sensing inhibitors, antimicrobial peptides, topical dressings, and antimicrobial photo-dynamic therapy. According to our review of the literature, targeting of biofilm is an important therapeutic choice in acute and chronic infected skin wounds both to overcome antibiotic resistance and to achieve better wound healing.

Fatty acid modified-antimicrobial peptide analogues with potent antimicrobial activity and topical therapeutic efficacy against Staphylococcus hyicus

There is an urgent need to explore new antimicrobial agents due to the looming threat of bacteria resistance. Bovine lactoferricin (LfcinB), as a multifunctional peptide, has the potential to be a new active drug in the future. In this study, it aims to investigate the effect of fatty acid conjugation on antimicrobial peptide activity and topical therapeutic efficacy in a mouse model infected with Staphylococcus hyicus. Both Lfcin4 and Lfcin5 were conjugated with the unsaturated fatty acid linoleic acid (18-C) at their N-terminus and modified by acylation at the C-terminus. The derived peptides of Lin-Lf4NH2 and Lin-Lf5NH2 showed better antibacterial activity (MICs of 3.27 to 6.64 μM) than their parent peptides (MICs of 1.83 to 59.57 μM). Lin-Lf4NH2 (63.2%, 5 min) and Lin-Lf5NH2 (35.8%, 5 min) could more rapidly penetrate bacterial membrane than Lf4NH2 (2.34%, 5 min) and Lf5NH2 (1.94%, 5 min), which further confirmed by the laser scanning confocal microscopy (LSCM). Electron microscopy observations showed Lin-Lf4NH2 and Lin-Lf5NH2 disrupted S. hyicus cell membranes and led to the leakage of contents. Furthermore, after treatment with Lin-Lf4NH2 and Lin-Lf5NH2, the abscess symptoms of mice were significantly alleviated; the recovery rate of abscesses scope of Lin-Lf4NH2 (73.25%) and Lin-Lf5NH2 (71.71%) were 38.8 and 37.9-fold higher than that of untreated group (1.89%), respectively, and superior to Lf4NH2 (46.87%) and Lf5NH2 (58.75%). They significantly reduced the bacterial load and the levels of the pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and chemokine (MCP-1) in S. hyicus skin lesions. This study provides evidence that conjugation of a fatty acid to antimicrobial peptides can improve the activity and have potential for topical therapeutic of S. hyicus skin infections. KEY POINTS: • Lin-Lfcin4NH2/Lfcin5NH2 showed stronger antimicrobial activity than parent peptides. • Lin-Lfcin4NH2/Lfcin5NH2 had a more effective ability to destroy bacterial membranes. • Lin-Lfcin4NH2/Lfcin5NH2 showed a topically higher efficacy than parent peptides.

Pulmonary biofilm-based chronic infections and inhaled treatment strategies

Certain pulmonary diseases, such as cystic fibrosis (CF), non-CF bronchiectasis, chronic obstructive pulmonary disease, and ventilator-associated pneumonia, are usually accompanied by respiratory tract infections due to the physiological alteration of the lung immunological defenses. Recurrent infections may lead to chronic infection through the formation of biofilms. Chronic biofilm-based infections are challenging to treat using antimicrobial agents. Therefore, effective ways to eradicate biofilms and thus relieve respiratory tract infection require the development of efficacious agents for biofilm destruction, the design of delivery carriers with biofilm-targeting and/or penetrating abilities for these agents, and the direct delivery of them into the lung. This review provides an in-depth description of biofilm-based infections caused by pulmonary diseases and focuses on current existing agents that are administered by inhalation into the lung to treat biofilm, which include i) inhalable antimicrobial agents and their combinations, ii) non-antimicrobial adjuvants such as matrix-targeting enzymes, mannitol, glutathione, cyclosporin A, and iii) liposomal formulations of anti-biofilm agents. Finally, novel agents that have shown promise against pulmonary biofilms as well as traditional and new devices for pulmonary delivery of anti-biofilm agents into the lung are also discussed.

Design and Pharmacodynamics of Recombinant Fungus Defensin NZL with Improved Activity against Staphylococcus hyicus In Vitro and In Vivo

Staphylococcus hyicus is recognized as a leading pathogen of exudative epidermitis in modern swine industry. Antimicrobial peptides are attractive candidates for development as potential therapeutics to combat the serious threats of the resistance of S. hyicus. In this study, a series of derivatives were designed based on the NZ2114 template with the aim of obtaining peptides with more potent antimicrobial activity through changing net positive charge or hydrophobicity. Among them, a variant designated as NZL was highly expressed in Pichia pastoris (P. pastoris) with total secreted protein of 1505 mg/L in a 5-L fermenter and exhibited enhanced antimicrobial activity relative to parent peptide NZ2114. Additionally, NZL could kill over 99% of S. hyicus NCTC10350 in vitro within 8 h and in Hacat cells. The results of membrane permeabilization assay, morphological observations, peptide localization assay showed that NZL had potent activity against S. hyicus, which maybe kill S. hyicus through action on the cell wall. NZL also showed an effective therapy in a mouse peritonitis model caused by S. hyicus, superior to NZ2114 or ceftriaxone. Overall, these findings can contribute to explore a novel potential candidate against S. hyicus infections.

Design and High Expression of Non-glycosylated Lysostaphins in Pichia pastoris and Their Pharmacodynamic Study

Lysostaphin is an effective antimicrobial agent to Staphylococcus, especially for the methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Staphylococcus aureus (MDRSA). In this study, the seven lysostaphin derived mutants (rLys) were designed to overcome the barrier of glycosylation during expression in Pichia pastoris. Among them, 127A and 127A232Q had highest antimicrobial activity (MIC values 0.07–0.3 μM) to S. aureus than others and the commercial lysostaphins (1–15.8 times). There was no glycosylation during the expression in 5-L fermenter level, with the high yield of 1315 mg/L (127A) and 1141 mg/L (127A232Q), respectively. Meanwhile, 127A and 127A232Q effectively killed 99.9% of S. aureus at low concentration (1 × MIC) within 30 min, without the regrowth of pathogen. They also showed low toxicity, high pH and temperature stability. The results of in vivo therapeutic effect of 127A and 127A232Q against high virulent S. aureus CVCC546 showed that 127A and 127A232Q increased the survival rate of infected mice up to 100% at the dose of 10 mg/kg than the untreated group, reduced the bacterial translocation by 5-7 log CFU (over 99%) in organs compared to the untreated group and alleviated multiple-organ injuries (liver, kidney and spleen). These data indicated that the non-glycosylated lysostaphin 127A and 127A232Q may be a promising therapeutic agent against MDR staphylococcal infections.

Repurposing celecoxib analogues as leads for antibiotics

There is an urgent need for new antibiotics and alternative strategies to combat bacterial pathogens. Molecular docking, antibacterial evaluation in vitro and in vivo, cytotoxicity assessment and enzyme inhibition analyses were performed. Compound 12 exhibited antimicrobial activity against Staphylococcus aureus (MIC: 4 μg/ml), various clinically isolated strains of MRSA (MIC: 4-16 μg/ml) and Acinetobacter baumannii (MIC: 4 μg/ml) when combined with subinhibitory concentrations of colistin B. Compound 12 (20 mg/kg) yielded mild improvement in survival of methicillin-resistant Staphylococcus aureus (MRSA)-infected mice. Additionally, enzyme inhibition tests showed that compound 12 exhibited inhibitory effects against S. aureus dihydrofolate reductase (105.1 μg/ml) and DNA gyrase (122.8 μg/ml). Compound 12 is a promising antibacterial candidate for further development.

Design of a novel antimicrobial peptide 1018M targeted ppGpp to inhibit MRSA biofilm formation

Methicillin-resistant staphylococcus aureus (MRSA) and its biofilm infection were considered as one of the main international health issues. There are still many challenges for treatment using traditional antibiotics. In this study, a mutant peptide of innate defense regulator (IDR-)1018 named 1018M was designed based on molecular docking and amino acid substitution technology. The antibacterial/biofilm activity and mechanisms against MRSA of 1018M were investigated for the first time. The minimum inhibitory concentration (MIC) of 1018M was reduced 1 time (MIC = 2 μg/mL) compared to IDR-1018. After treatment with 32 μg/mL 1018M for 24 h, the percentage of biofilm decreased by 78.9%, which was more effective than the parental peptide. The results of mechanisms exploration showed that 1018M was more potent than IDR-1018 at destructing bacterial cell wall, permeating cell membrane (20.4%–50.1% vs 1.45%–10.6%) and binding to stringent response signaling molecule ppGpp (increased 27.9%). Additionally, the peptides could also exert their activity by disrupting genomic DNA, regulating the expression of ppGpp metabolism and biofilm forming related genes (RSH, relP, relQ, rsbU, sigB, spA, codY, agrA and icaD). Moreover, the higher temperature, pH and pepsase stabilities provide 1018M better processing, storage and internal environmental tolerance. These data indicated that 1018M may be a potential candidate peptide for the treatment of MRSA and its biofilm infections.

Marine Peptide-N6NH2 and Its Derivative-GUON6NH2 Have Potent Antimicrobial Activity Against Intracellular Edwardsiella tarda in vitro and in vivo

Edwardsiella tarda is a facultative intracellular pathogen in humans and animals. There is no effective way except vaccine candidates to eradicate intracellular E. tarda. In this study, four derivatives of marine peptide-N6NH2 were designed by an introduction of unnatural residues or substitution of natural ones, and their intracellular activities against E. tarda were evaluated in macrophages and in mice, respectively. The minimum inhibitory concentration (MIC) value of N6NH2 and GUON6NH2 against E. tarda was 8 μg/mL. GUON6NH2 showed higher stability to trypsin, lower toxicity (<1%) and longer post-antibiotic effect (PAE) than N6NH2 and other derivatives. Antibacterial mechanism results showed that GUON6NH2 could bind to LPS and destroyed outer/inner cell membranes of E. tarda, superior to N6NH2 and norfloxacin. Both N6NH2 and GUON6NH2 were internalized into macrophages mainly via lipid rafts, micropinocytosis, and microtubule polymerization, respectively, and distributed in the cytoplasm. The intracellular inhibition rate of GUON6NH2 against E. tarda was 97.05–100%, higher than that in case of N6NH2 (96.82–100%). In the E. tarda-induced peritonitis mouse model, after treatment with of 1 μmol/kg N6NH2 and GUON6NH2, intracellular bacterial numbers were reduced by 1.54- and 1.97-Log₁₀ CFU, respectively, higher than norfloxacin (0.35-Log₁₀ CFU). These results suggest that GUON6NH2 may be an excellent candidate for novel antimicrobial agents to treat infectious diseases caused by intracellular E. tarda.

A Novel Ivermectin-Derived Compound D4 and Its Antimicrobial/Biofilm Properties against MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) and its biofilms infection is still a serious threat to global health. It is urgent to develop efficient drugs by repositioning or designing drugs to solve this problem. In this study, the antibacterial/biofilm activity and mechanisms of ivermectin (D) and its 4″-position amino substitution derivative (D4) against MRSA were investigated. The minimum inhibitory concentration (MIC) of D was 20 μg/mL, which is four times higher than D4 (MIC = 5 μg/mL). The mechanism research demonstrated that D4 was more potent than D at destroying bacterial cell wall, permeating cell membrane (6.25-36.0% vs 1.92-6.04%) and binding to MRSA genomic DNA. Moreover, after incubation with 10-40 μg/mL D4 for 24 h, the percentages of biofilm decreased by 21.2-92.9%, which was more effective than D (no significant change at 40 μg/mL). The antibiofilm effect is achieved by regulating the expression of related genes (RSH, relQ, rsbU, sigB, spA, and icaD). Additionally, though the higher hemolysis makes D4 a safety risk for intravenous injection, other administration options could be considered as well. Therefore, all the results have indicated that D4 may be a potential candidate compound for the treatment of MRSA and its biofilm infections.

A recombinant fungal defensin-like peptide-P2 combats Streptococcus dysgalactiae and biofilms

Streptococcus dysgalactiae, considered one of the main pathogens that causes bovine mastitis, is a serious threat to humans and animals. However, the excessive use of antibiotics and the characteristic of S. dysgalactiae forming biofilms in mastitic teat canal have serious clinical implications. In this study, in vivo and in vitro multiple mechanisms of action of P2, a mutant of fungal defensin plectasin, against S. dysgalactiae were systematically and comprehensively investigated for the first time. P2 showed potent antibacterial activity against S. dysgalactiae (minimum inhibitory concentration, MIC = 0.23-0.46 μM) and rapid bactericidal action by 3.0 lg units reduction in 2-4 h. No resistant mutants appeared after 30-d serial passage of S. dysgalactiae in the presence of P2. The results of electron microscopy and flow cytometer showed that P2 induced membrane damage of S. dysgalactiae, causing the leakage of cellular content and eventually cell death. Besides, P2 effectively inhibited early biofilm formation, eradicated mature biofilms, and killed 99.9% persisters which were resistant to 100 × MIC vancomycin; and confocal laser scanning microscopy (CLSM) also revealed the potent antibacterial and antibiofilm activity of P2 (the thickness of biofilm reduced from 18.82 to 7.94 μm). The in vivo therapeutic effect of P2 in mouse mastitis model showed that it decreased the number of mammary bacteria and alleviated breast inflammation by regulating cytokines and inhibiting bacterial proliferation, which were superior to vancomycin. These data indicated that P2 maybe a potential candidate peptide for mastitis treatment of S. dysgalactiae infections. KEY POINTS: •P2 showed potential in vitro antibacterial characteristics towards S. dysgalactiae. •P2 eradicated biofilms, killed persisters, and induced cell death of S. dysgalactiae. •P2 could effectively protect mice from S. dysgalactiae infection in gland.

Dual Antibacterial Activities and Biofilm Eradication of a Marine Peptide-N6NH2 and Its Analogs against Multidrug-Resistant Aeromonas veronii

Aeromonas veronii is one of the main pathogens causing various diseases in humans and animals. It is currently difficult to eradicate drug-resistant A. veronii due to the biofilm formation by conventional antibiotic treatments. In this study, a marine peptide-N6NH2 and its analogs were generated by introducing Orn or replacing with D-amino acids, Val and Pro; their enzymic stability and antibacterial/antibiofilm ability against multi-drug resistant (MDR) A. veronii ACCC61732 were detected in vitro and in vivo, respectively. The results showed that DN6NH2 more rapidly killed A. veronii ACCC61732 and had higher stability in trypsin, simulated gastric/intestinal fluid, proteinase K, and mouse serum than the parent peptide-N6NH2. DN6NH2 and other analogs significantly improved the ability of N6NH2 to penetrate the outer membrane of A. veronii ACCC61732. DN6NH2, N6PNH2 and V112N6NH2 protected mice from catheter-associated biofilm infection with MDR A. veronii ACCC61732, superior to N6NH2 and CIP. DN6NH2 had more potent efficacy at a dose of 5 μmol/kg (100% survival) in a mouse peritonitis model than other analogs (50-66.67%) and CIP (83.33%), and it inhibited the bacterial translocation, downregulated pro-inflammatory cytokines, upregulated the anti-inflammatory cytokine, and ameliorated multiple-organ injuries (including the liver, spleen, lung, and kidney). These data suggest that the analogs of N6NH2 may be a candidate for novel antimicrobial and antibiofilm agents against MDR A. veronii infections.

A Review on the Use of Antimicrobial Peptides to Combat Porcine Viruses

Viral infectious diseases pose a serious threat to animal husbandry, especially in the pig industry. With the rapid, continuous variation of viruses, a series of therapeutic measures, including vaccines, have quickly lost their efficacy, leading to great losses for animal husbandry. Therefore, it is urgent to find new drugs with more stable and effective antiviral activity. Recently, it has been reported that antimicrobial peptides (AMPs) have great potential for development and application in animal husbandry because of their significant antibacterial and antiviral activity, and the antiviral ability of AMPs has become a research hotspot. This article aims to review the research situation of AMPs used to combat viruses in swine production of animal husbandry, clarify the mechanism of action of AMPs on viruses and raise some questions, and explore the future potential of AMPs in animal husbandry.

An Enhanced Variant Designed From DLP4 Cationic Peptide Against Staphylococcus aureus CVCC 546

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 was 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 MIC 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 potassium ion leakage; it bound to genomic DNA (gDNA) and led 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 post-antibiotic effect (PAE) of 12.78 ± 0.28 h, and 10 mg/kg ID13 caused a 1.8 log10 (CFU/g) (CFU: colony-forming units) reduction of S. aureus in infected mouse thigh 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.

Strategies to Combat Multidrug-Resistant and Persistent Infectious Diseases

Antibiotic failure is one of the most worrying health problems worldwide. We are currently facing an international crisis with several problematic facets: new antibiotics are no longer being discovered, resistance mechanisms are occurring in almost all clinical isolates of bacteria, and recurrent infections caused by persistent bacteria are hampering the successful treatment of infections. In this context, new anti-infectious strategies against multidrug-resistant (MDR) and persistent bacteria, as well as the rescue of Food and Drug Administration (FDA)-approved compounds (drug repurposing), are being explored. Among the highlighted new anti-infectious strategies, in this review, we focus on antimicrobial peptides, anti-virulence compounds, phage therapy, and new molecules. As drugs that are being repurposed, we highlight anti-inflammatory compounds, anti-psychotics, anti-helminthics, anti-cancerous drugs, and statins.

Recombinant of the Staphylococcal Bacteriophage Lysin CHAPk and Its Elimination against Streptococcus agalactiae Biofilms

Bovine mastitis is the most important infectious disease, causing significant losses in the dairy industry, in which Streptococcus agalactiae is a major pathogen. In this study, lysin CHAP_k, derived from bacteriophage K, was expressed heterogeneously, and its antimicrobial and anti-biofilm effects against S. agalactiae isolated from bovine mastitis were further analyzed. CHAP_k was expressed in Escherichia coli BL21 (DE3), in which the purified yield of CHAP_k was up to 14.6 mg/L with the purity of 95%. Time-killing kinetic curves showed that CHAP_k fastly killed S. agalactiae in TSB medium and in milk within 25 min (by 3.3 log₁₀ CFU/mL and 2.4 log₁₀ CFU/mL, respectively). Observation of scanning electron microscope (SEM) showed cells wrinkled and ruptured after the treatment of CHAP_k. CHAP_k effectively inhibited early biofilms by 95% in 8 × MIC, and eradicated mature biofilms by 89.4% in 16 × MIC. Moreover, CHAP_k killed 99% bacteria in mature biofilms. Confocal laser scanning microscopy (CLSM) also demonstrated the potent antimicrobial and anti-biofilm action of CHAP_k. It was firstly demonstrated CHAP_k had the characters of inhibition/elimination of S. agalactiae biofilms and killing the bacteria in biofilms. CHAP_k has the potential to develop a new antibacterial agent for mastitis treatment of S. agalactiae infections.

A new high-yielding antimicrobial peptide NZX and its antibacterial activity against Staphylococcus hyicus in vitro/vivo

Staphylococcus hyicus, considered as a leading pathogen of exudative epidermitis, is a serious threat to humans and animals. The emergency of bacterial resistance to antibiotics, especially in human and animal health fields, leads to an urgent need of exploration of new antimicrobial agents. In this study, NZX, a plectasin-derived peptide, was firstly expressed in Pichia pastoris X-33 and was purified by cation exchange chromatography, followed by detection of its antibacterial activity in vitro and in vivo. The results showed that the total secreted protein concentration in fermentation supernatant was up to 2820 mg/L (29 °C) after 120-h induction in a 5-L fermentor. The yield of NZX reached up to 965 mg/L with a purity of 92.6%. The recombinant expressed NZX had a strong antimicrobial activity, high stability, and low toxicity. The minimal inhibitory concentrations (MICs) of NZX and ceftriaxone (CRO) against Gram-positive bacteria were 0.46 to 0.91 μM and 6.04 to 12.09 μM, respectively. The time-killing curves showed that S. hyicus NCTC10350 was killed completely by 2× and 4 × MIC of NZX within 24 h. NZX also exhibited the intracellular activity against S. hyicus in Hacat cells. After treatment with NZX (10 mg/kg) and CRO (60 mg/kg), the survival rates of mice were 100% and 83.3%, respectively. NZX inhibited the bacterial translocation, downregulated pro-inflammatory cytokines (TNF-α/IL-1β/IL-6), upregulated the anti-inflammatory cytokine (IL-10), and ameliorated multiple-organ injuries (the liver, spleen, lung, and kidney). This study provides evidence that the expressed NZX has the potential to become a powerful candidate as novel antimicrobial agents against S. hyicus infections.