Lung antimicrobial proteins and peptides: From host defense to therapeutic strategies.

Representing severe morbidity and mortality globally, respiratory infections associated with chronic respiratory diseases, including complicated pneumonia, asthma, interstitial lung disease, and chronic obstructive pulmonary disease, are a major public health concern. Lung health and the prevention of pulmonary disease rely on the mechanisms of airway surface fluid secretion, mucociliary clearance, and adequate immune response to eradicate inhaled pathogens and particulate matter from the environment. The antimicrobial proteins and peptides contribute to maintaining an antimicrobial milieu in human lungs to eliminate pathogens and prevent them from causing pulmonary diseases. The predominant antimicrobial molecules of the lung environment include human α- and ß-defensins and cathelicidins, among numerous other host defense molecules with antimicrobial and antibiofilm activity such as PLUNC (palate, lung, and nasal epithelium clone) family proteins, elafin, collectins, lactoferrin, lysozymes, mucins, secretory leukocyte proteinase inhibitor, surfactant proteins SP-A, and SP-D, and RNases. It has been demonstrated that changes in antimicrobial molecule expression levels are associated with regulating inflammation, potentiating exacerbations, pathological changes, and modifications in chronic lung disease severity. Antimicrobial molecules also display roles in both anticancer and tumorigenic effects. Lung antimicrobial proteins and peptides are promising alternative therapeutics for treating and preventing multidrug-resistant bacterial infections and anticancer therapies.

Host antimicrobial peptide S100A12 disrupts the fungal membrane by direct binding and inhibits growth and biofilm formation of Fusarium species.

Fungal keratitis is the foremost cause of corneal infections worldwide, of which Fusariumspp. is the common etiological agent that causes loss of vision and warrants surgical intervention. An increase in resistance to the available drugs along with severe side effects of the existing antifungals demands for new effective antimycotics. Here, we demonstrate that antimicrobial peptide S100A12 directly binds to the phospholipids of the fungal membrane, disrupts the structural integrity, and induces generation of reactive oxygen species in fungus. In addition, it inhibits biofilm formation by Fusariumspp. and exhibits antifungal property against Fusariumspp. both in vitro and in vivo. Taken together, our results delve into specific effect of S100A12 against Fusariumspp. with an aim to investigate new antifungal compounds to combat fungal keratitis.

The role of morphine- and fentanyl-induced impairment of intestinal epithelial antibacterial activity in dysbiosis and its impact on the microbiota-gut-brain axis.

Recent evidence suggests that chronic exposure to opioid analgesics such as morphine disrupts the intestinal epithelial layer and causes intestinal dysbiosis. Depleting gut bacteria can preclude the development of tolerance to opioid-induced antinociception, suggesting an important role of the gut-brain axis in mediating opioid effects. The mechanism underlying opioid-induced dysbiosis, however, remains unclear. Host-produced antimicrobial peptides (AMPs) are critical for the integrity of the intestinal epithelial barrier as they prevent the pathogenesis of the enteric microbiota. Here, we report that chronic morphine or fentanyl exposure reduces the antimicrobial activity in the ileum, resulting in changes in the composition of bacteria. Fecal samples from morphine-treated mice had increased levels of Akkermansia muciniphila with a shift in the abundance ratio of Firmicutes and Bacteroidetes. Fecal microbial transplant (FMT) from morphine-naïve mice or oral supplementation with butyrate restored (a) the antimicrobial activity, (b) the expression of the antimicrobial peptide, Reg3γ, (c) prevented the increase in intestinal permeability and (d) prevented the development of antinociceptive tolerance in morphine-dependent mice. Improved epithelial barrier function with FMT or butyrate prevented the enrichment of the mucin-degrading A. muciniphila in morphine-dependent mice. These data implicate impairment of the antimicrobial activity of the intestinal epithelium as a mechanism by which opioids disrupt the microbiota-gut-brain axis.

Structural Classification Insights Into the Plant Defensive Peptides.

This study presents a structural phylogenetic analysis of plant defensive peptides, revealing their evolutionary relationships, structural diversification, and functional adaptations. Utilizing a robust dataset comprising both experimental and predicted structures sourced from the RCSB Protein Data Bank and AlphaFold DB, we constructed a detailed phylogenetic tree to elucidate the distinct evolutionary paths of plant defensive peptide families. Our findings showcase the evolutionary intricacies of defensive peptides, highlighting their diversity and the conservation of key structural motifs critical to their antimicrobial or defensive functions. The results also underscore the adaptive significance of defensive peptides in plant evolution, highlighting their roles in responding to ecological pressures and pathogen interactions.

Intercalated cell function, kidney innate immunity, and urinary tract infections.

Intercalated cells (ICs) in the kidney collecting duct have a versatile role in acid-base and electrolyte regulation along with the host immune defense. Located in the terminal kidney tubule segment, ICs are among the first kidney cells to encounter bacteria when bacteria ascend from the bladder into the kidney. ICs have developed several mechanisms to combat bacterial infections of the kidneys. For example, ICs produce antimicrobial peptides (AMPs), which have direct bactericidal activity, and in many cases are upregulated in response to infections. Some AMP genes with IC-specific kidney expression are multiallelic, and having more copies of the gene confers increased resistance to bacterial infections of the kidney and urinary tract. Similarly, studies in human children demonstrate that those with history of UTIs are more likely to have single-nucleotide polymorphisms in IC-expressed AMP genes that impair the AMP's bactericidal activity. In murine models, depleted or impaired ICs result in decreased clearance of bacterial load following transurethral challenge with uropathogenic E. coli. A 2021 study demonstrated that ICs even act as phagocytes and acidify bacteria within phagolysosomes. Several immune signaling pathways have been identified in ICs which may represent future therapeutic targets in managing kidney infections or inflammation. This review's objective is to highlight IC structure and function with an emphasis on current knowledge of IC's diverse innate immune capabilities.

Significance of CD10 for Mucosal Immunomodulation by ß-Casomorphin-7 in Exacerbation of Ulcerative Colitis.

ß-Casomorphin-7 (BCM), a breakdown product of milk ß-casein, exhibits opioid activity. Opioids are known to affect the immune system, but the effects of BCM on ulcerative colitis (UC) are not clear. We examined the effects of BCM on mucosal immunity using a mouse dextran sulfate sodium-induced colitis model and an in vitro CD8+ T cell activation model. Human UC patients were examined to reveal the relationship between CD10 and mucosal immunity. Combined treatment of the colitis model with thiorphan (TOP) inhibited BCM degradation by suppressing CD10 in the intestinal mucosa, activating mouse mucosal CD8, and suppressing CD4 and Treg. In the CD8+ T cell in vitro activation assay using mouse splenocytes, BCM inhibited the oxidative phosphorylation (OXPHOS) of CD8+ T cells and induced the glycolytic pathway, promoting their activation. Conversely, in a culture system, BCM suppressed OXPHOS and decreased defensin α production in IEC6 mouse intestinal epithelial cells. In the mouse model, BCM reduced defensin α and butyrate levels in the colonic mucosa. During the active phase of human ulcerative colitis, the downward regulation of ileal CD10 expression by CpG methylation of the gene promoter was observed, resulting in increased CD8 activation and decreased defensin α and butyrate levels. BCM is a potential aggravating factor for UC and should be considered in the design of dietary therapy. In addition, decreased CD10 expression may serve as an indicator of UC activity and recurrence, but further clinical studies are needed.

Effect of tryptophan position and lysine/arginine substitution in antimicrobial peptides on antifungal action.

Every year, the overprescription, misuse, and improper disposal of antibiotics have led to the rampant development of drug-resistant pathogens and, in turn, a significant increase in the number of patients who die of drug-resistant fungal infections. Recently, researchers have begun investigating the use of antimicrobial peptides (AMPs) as next-generation antifungal agents to inhibit the growth of drug-resistant fungi. The antifungal activity of alpha-helical peptides designed using the cationic amino acids containing lysine and arginine and the hydrophobic amino acids containing isoleucine and tryptophan were evaluated using 10 yeast and mold fungi. Among these peptides, WIK-14, which is composed of a 14-mer with tryptophan sequences at the amino terminus, showed the best antifungal activity via transient pore formation and ROS generation. In addition, the in vivo antifungal effects of WIK-14 were investigated in a mouse model infected with drug-resistant Candida albicans. The results demonstrate the potential of AMPs as antifungal agents.

Vitamin D triggers hCAP18/LL-37 production: Implications for LL-37-induced human osteoblast cytotoxicity.

The human cathelicidin LL-37 shows activity against microorganisms, but it is also cytotoxic to host cells. The CAMP gene codes for the LL-37 precursor hCAP18 which is processed extracellularly to active LL-37. It has previously been shown that vitamin D stimulates CAMP gene activity, but less information is available demonstrating that vitamin D also can increase hCAP18/LL-37 protein production. Here, we show with RT-qPCR that a physiological concentration of vitamin D (50 nM) enhances CAMP mRNA levels by about 170 times in human THP-1 monocyte cells. Stimulation with 50 nM vitamin D increases hCAP18/LL-37 protein contents 3-4 times in THP-1 cell lysates demonstrated by both dot blot analysis and ELISA applying two different hCAP18/LL-37 antibodies. Treatment with the proteasome inhibitor MG132 enhances hCAP18/LL-37 levels, suggesting that turnover of hCAP18/LL-37 protein is regulated by the proteasome. The hCAP18/LL-37 concentration in vitamin D-stimulated THP-1 cells corresponds to 1.04 µM LL-37. Interestingly, synthetic LL-37, at this concentration, reduces viability of human osteoblast-like MG63 cells, whereas the THP-1 cells are less sensitive as demonstrated by the MTT assay. In summary, we show that vitamin D enhances hCAP18/LL-37 production, and that this effect can be of physiological/pathophysiological relevance for LL-37-induced human osteoblast toxicity.

Combined effect of SAR-endolysin LysKpV475 with polymyxin B and Salmonella bacteriophage phSE-5.

Endolysins are bacteriophage (or phage)-encoded enzymes that catalyse the peptidoglycan breakdown in the bacterial cell wall. The exogenous action of recombinant phage endolysins against Gram-positive organisms has been extensively studied. However, the outer membrane acts as a physical barrier when considering the use of recombinant endolysins to combat Gram-negative bacteria. This study aimed to evaluate the antimicrobial activity of the SAR-endolysin LysKpV475 against Gram-negative bacteria as single or combined therapies, using an outer membrane permeabilizer (polymyxin B) and a phage, free or immobilized in a pullulan matrix. In the first step, the endolysin LysKpV475 in solution, alone and combined with polymyxin B, was tested in vitro and in vivo against ten Gram-negative bacteria, including highly virulent strains and multidrug-resistant isolates. In the second step, the lyophilized LysKpV475 endolysin was combined with the phage phSE-5 and investigated, free or immobilized in a pullulan matrix, against Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311. The bacteriostatic action of purified LysKpV475 varied between 8.125 µg ml-1 against Pseudomonas aeruginosa ATCC 27853, 16.25 µg ml-1 against S. enterica Typhimurium ATCC 13311, and 32.50 µg ml-1 against Klebsiella pneumoniae ATCC BAA-2146 and Enterobacter cloacae P2224. LysKpV475 showed bactericidal activity only for P. aeruginosa ATCC 27853 (32.50 µg ml-1) and P. aeruginosa P2307 (65.00 µg ml-1) at the tested concentrations. The effect of the LysKpV475 combined with polymyxin B increased against K. pneumoniae ATCC BAA-2146 [fractional inhibitory concentration index (FICI) 0.34; a value lower than 1.0 indicates an additive/combined effect] and S. enterica Typhimurium ATCC 13311 (FICI 0.93). A synergistic effect against S. enterica Typhimurium was also observed when the lyophilized LysKpV475 at ⅔ MIC was combined with the phage phSE-5 (m.o.i. of 100). The lyophilized LysKpV475 immobilized in a pullulan matrix maintained a significant Salmonella reduction of 2 logs after 6 h of treatment. These results demonstrate the potential of SAR-endolysins, alone or in combination with other treatments, in the free form or immobilized in solid matrices, which paves the way for their application in different areas, such as in biocontrol at the food processing stage, biosanitation of food contact surfaces and biopreservation of processed food in active food packing.

Endogenous Antimicrobial-Immunomodulatory Molecules: Networking Biomolecules of Innate Immunity.

Endogenous antimicrobial-immunomodulatory molecules (EAIMs) are essential to immune-mediated human health and evolution. Conventionally, antimicrobial peptides (AMPs) have been regarded as the dominant endogenous antimicrobial molecule; however, AMPs are not sufficient to account for the full spectrum of antimicrobial-immunomodulatory duality occurring within the human body. The threat posed by pathogenic microbes is pervasive with the capacity for widespread impact across many organ systems and multiple biochemical pathways; accordingly, the host needs the capacity to react with an equally diverse response. This can be attained by having EAIMs that traverse the full range of molecular size (small to large molecules) and structural diversity (including molecules other than peptides). This review identifies multiple molecules (peptide/protein, lipid, carbohydrate, nucleic acid, small organic molecule, and metallic cation) as EAIMs and discusses the possibility of cooperative, additive effects amongst the various EAIM classes during the host response to a microbial assault. This comprehensive consideration of the full molecular diversity of EAIMs enables the conclusion that EAIMs constitute a previously uncatalogued structurally diverse and collectively underappreciated immuno-active group of integrated molecular responders within the innate immune system's first line of defence.

Ursoricin, a bacteriocin of Streptococcus ursoris, has potent activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci.

The emergence of drug-resistant bacteria, particularly methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE), has increased the need to discover novel antimicrobial agents that are effective against these species. Here, we describe the identification and purification of the mutacin BHT-B-like gene locus and bacteriocin peptide from Streptococcus ursoris, which is closely related to Streptococcus ratti; hence, we named this bacteriocin ursoricin. Ursoricin is a cationic, chromosome-encoded peptide that has potent antimicrobial effects against Gram-positive pathogens, including MRSA and VRE, with minimum inhibitory concentrations in the micromolar range. Ursoricin also inhibits the biofilm formation of high biofilm-forming S. aureus. Antibacterial activity was retained after treatment at 100°C for 60 min at a pH range of 3-9 and was partially reduced by treatment with proteinase K for 2 h (63% residual activity). The potent anti-MRSA, anti-VRE, and antibiofilm effects of ursoricin suggest that it is a possible candidate for the treatment of MRSA, VRE, and biofilm-associated infections. IMPORTANCE: The emergence of multidrug-resistant bacteria worldwide has posed a significant public health threat and economic burdens that make the identification and development of novel antimicrobial agents urgent. Bacteriocins are promising new agents that exhibit antibacterial activity against a wide range of human pathogens. In this study, we report that the bacteriocin produced by Streptococcus ursoris showed good antibacterial activity against a wide range of Staphylococcus aureus and enterococcus strains, particularly methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and high biofilm-forming S. aureus. Interestingly, this bacteriocin had a stronger effect on S. aureus than on Staphylococcus epidermidis, which is a major commensal bacterium in human skin; this result is important when considering the disturbance of bacterial flora, especially on the skin, mediated by the application of antibacterial agents.

Acute salivary antimicrobial peptide secretion response to different exercise intensities and durations.

Antimicrobial peptides, key players of innate mucosal immunity in the oral cavity, exert antibacterial and bacteriolytic effects. This study aimed to clarify the effects of acute exercise at different intensities and durations on salivary antimicrobial peptide levels. In a randomized crossover trial, 14 young healthy untrained men performed intensity trials (cycling at 35%, 55%, and 75% of maximal oxygen uptake [VO2max] for 30 min) and duration trials (cycling at 55% VO2max for 30, 60, and 90 min). Saliva samples were collected at baseline and 0 and 60 min after exercise. In intensity trials, the change in salivary Lactoferrin levels from baseline to 0 min after 30-min exercise was greater at 75% VO2max exercise intensity compared to that at 35% VO2max. Furthermore, the change in salivary human beta defensin-2 (HBD-2) levels was greater at 75% VO2max compared to that at 35% and 55% VO2max. Salivary Lysozyme levels increased after exercise, independent of exercise intensity. However, salivary LL-37 levels did not change after exercise at any intensity. Additionally, in duration trials, the change in salivary levels of LL-37 and HBD-2 from baseline to 0 min after exercise at 55% VO2max was greater after 60 min and 90 min of exercise compared to that after 30 min of exercise. However, salivary Lactoferrin and Lysozyme levels increased after exercise, independent of exercise duration. Our findings suggest that secretory responses to acute exercise with exercise intensity and duration differ among salivary antimicrobial peptides.

Genetically-clustered antifungal phytocytokines and receptor protein family members cooperate to trigger plant immune signaling.

Phytocytokines regulate plant immunity by cooperating with cell-surface proteins. Populus trichocarpa RUST INDUCED SECRETED PEPTIDE 1 (PtRISP1) exhibits an elicitor activity in poplar, as well as a direct antimicrobial activity against rust fungi. PtRISP1 gene directly clusters with a gene encoding a leucine-rich repeat receptor protein (LRR-RP), that we termed RISP-ASSOCIATED LRR-RP (PtRALR). In this study, we used phylogenomics to characterize the RISP and RALR gene families, and molecular physiology assays to functionally characterize RISP/RALR pairs. Both RISP and RALR gene families specifically evolved in Salicaceae species (poplar and willow), and systematically cluster in the genomes. Despite a low sequence identity, Salix purpurea RISP1 (SpRISP1) shows properties and activities similar to PtRISP1. Both PtRISP1 and SpRISP1 induced a reactive oxygen species (ROS) burst and mitogen-activated protein kinases (MAPKs) phosphorylation in Nicotiana benthamiana leaves expressing the respective clustered RALR. PtRISP1 also triggers a rapid stomatal closure in poplar. Altogether, these results suggest that plants evolved phytocytokines with direct antimicrobial activities, and that the genes coding these phytocytokines co-evolved and physically cluster with genes coding LRR-RPs required to initiate immune signaling.

Antibacterial mechanism and structure-activity relationships of Bombyx mori cecropin A.

Bombyx mori cecropin A (Bmcecropin A) has antibacterial, antiviral, anti-filamentous fungal and tumour cell inhibition activities and is considered a potential succedaneum for antibiotics. We clarified the antibacterial mechanism and structure-activity relationships and then directed the structure-activity optimization of Bmcecropin A. Firstly, we found Bmcecropin A shows a strong binding force and permeability to cell membranes like a detergent; Bmcecropin A could competitively bind to the cell membrane with the cell membrane-specific dye DiI, then damaged the membrane for the access of DiI into the cytoplasm and leading to the leakage of electrolyte and proteins. Secondly, we found Bmcopropin A could also bind to and degrade DNA; furthermore, DNA library polymerase chain reaction (PCR) results indicated that Bmcecropin A inhibited DNA replication by non-specific binding. In addition, we have identified C-terminus amidation and serine-lysine- glycine (SLG) amino acids of Bmcecropin A played critical roles in the membrane damage and DNA degradation. Based on the above results, we designed a mutant of Bmcecropin A (E9 to H, D17 to K, K33 to A), which showed higher antibacterial activity, thermostability and pH stability than ampicillin but no haemolytic activity. Finally, we speculated that Bmcecropin A damaged the cell membrane through a carpet model and drew the schematic diagram of its antibacterial mechanism, based on the antibacterial mechanism and the three-dimensional configuration. These findings yield insights into the mechanism of antimicrobial peptide-pathogen interaction and beneficial for the development of new antibiotics.

Structure-Activity Relationship Study to Develop Peptide Amphiphiles as Species-Specific Antimicrobials.

Antimicrobial peptide amphiphiles (PAs) are a promising class of molecules that can disrupt the bacterial membrane or act as drug nanocarriers. In this study, we prepared 33 PAs to establish supramolecular structure-activity relationships. We studied the morphology and activity of the nanostructures against different Gram-positive and Gram-negative bacterial strains (such as Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii). Next, we used principal component analysis (PCA) to determine the key contributors to activity. We found that for S. aureus, the zeta potential was the major contributor to the activity while Gram-negative bacteria were more influenced by the partition coefficient (LogP) with the following order P. aeruginosa>E. coli>A. baumannii. We also performed a study of the mechanism of action of selected PAs on the bacterial membrane assessing the membrane permeability and depolarization, changes in zeta potential and overall integrity. We studied the toxicity of the nanostructures against mammalian cells. Finally, we performed an in vivo study using the wax moth larvae to determine the therapeutic efficacy of the active PAs. This study shows cationic PA nanostructures can be an intriguing platform for the development of nanoantibacterials.

Functionalization of Alginate Hydrogels with a Multifunctional Peptide Supports Mesenchymal Stem Cell Adhesion and Reduces Bacterial Colonization.

Hydrogels with cell adhesive moieties stand out as promising materials to enhance tissue healing and regeneration. Nonetheless, bacterial infections of the implants represent an unmet major concern. In the present work, we developed an alginate hydrogel modified with a multifunctional peptide containing the RGD cell adhesive motif in combination with an antibacterial peptide derived from the 1-11 region of lactoferrin (LF). The RGD-LF branched peptide was successfully anchored to the alginate backbone by carbodiimide chemistry, as demonstrated by 1H NMR and fluorescence measurements. The functionalized hydrogel presented desirable physicochemical properties (porosity, swelling and rheological behavior) to develop biomaterials for tissue engineering. The viability of mesenchymal stem cells (MSCs) on the peptide-functionalized hydrogels was excellent, with values higher than 85 % at day 1, and higher than 95 % after 14 days in culture. Moreover, the biological characterization demonstrated the ability of the hydrogels to significantly enhance ALP activity of MSCs as well as to decrease bacterial colonization of both Gram-positive and Gram-negative models. Such results prove the potential of the functionalized hydrogels as novel biomaterials for tissue engineering, simultaneously displaying cell adhesive activity and the capacity to prevent bacterial contamination, a dual bioactivity commonly not found for these types of hydrogels.

Computer-made peptide RQ18 acts as a dual antifungal and antibiofilm peptide though membrane-associated mechanisms of action.

The spread of fungi resistant to conventional drugs has become a threatening problem. In this context, antimicrobial peptides (AMPs) have been considered as one of the main alternatives for controlling fungal infections. Here, we report the antifungal and antibiofilm activity and some clues about peptide RQ18's mechanism of action against Candida and Cryptococcus. This peptide inhibited yeast growth from 2.5 µM and killed all Candida tropicalis cells within 2 h incubation. Moreover, it showed a synergistic effect with antifungal agent the amphotericin b. RQ18 reduced biofilm formation and promoted C. tropicalis mature biofilms eradication. RQ18's mechanism of action involves fungal cell membrane damage, which was confirmed by the results of RQ18 in the presence of free ergosterol in the medium and fluorescence microscopy by Sytox green. No toxic effects were observed in murine macrophage cell lines and Galleria mellonella larvae, suggesting fungal target selectivity. Therefore, peptide RQ18 represents a promising strategy as a dual antifungal and antibiofilm agent that contributes to infection control without damaging mammalian cells.

Promising antibacterial efficacy of arenicin peptides against the emerging opportunistic pathogen Mycobacterium abscessus.

BACKGROUND: Mycobacterium abscessus, a fast-growing non-tuberculous mycobacterium, is an emerging opportunistic pathogen responsible for chronic bronchopulmonary infections in people with respiratory diseases such as cystic fibrosis (CF). Due to its intrinsic polyresistance to a wide range of antibiotics, most treatments for M. abscessus pulmonary infections are poorly effective. In this context, antimicrobial peptides (AMPs) active against bacterial strains and less prompt to cause resistance, represent a good alternative to conventional antibiotics. Herein, we evaluated the effect of three arenicin isoforms, possessing two or four Cysteines involved in one (Ar-1, Ar-2) or two disulfide bonds (Ar-3), on the in vitro growth of M. abscessus. METHODS: The respective disulfide-free AMPs, were built by replacing the Cysteines with alpha-amino-n-butyric acid (Abu) residue. We evaluated the efficiency of the eight arenicin derivatives through their antimicrobial activity against M. abscessus strains, their cytotoxicity towards human cell lines, and their hemolytic activity on human erythrocytes. The mechanism of action of the Ar-1 peptide was further investigated through membrane permeabilization assay, electron microscopy, lipid insertion assay via surface pressure measurement, and the induction of resistance assay. RESULTS: Our results demonstrated that Ar-1 was the safest peptide with no toxicity towards human cells and no hemolytic activity, and the most active against M. abscessus growth. Ar-1 acts by insertion into mycobacterial lipids, resulting in a rapid membranolytic effect that kills M. abscessus without induction of resistance. CONCLUSION: Overall, the present study emphasized Ar-1 as a potential new alternative to conventional antibiotics in the treatment of CF-associated bacterial infection related to M. abscessus.

Antibacterial activity of a short de novo designed peptide against fish bacterial pathogens.

In the face of increasing antimicrobial resistance in aquaculture, researchers are exploring novel substitutes to customary antibiotics. One potential solution is the use of antimicrobial peptides (AMPs). We aimed to design and evaluate a novel, short, and compositionally simple AMP with potent activity against various bacterial pathogens in aquaculture. The resulting peptide, KK12YW, has an amphipathic nature and net charge of + 7. Molecular docking experiments disclosed that KK12YW has a strong affinity for aerolysin, a virulence protein produced by the bacterial pathogen Aeromonas sobria. KK12YW was synthesized using Fmoc chemistry and tested against a range of bacterial pathogens, including A. sobria, A. salmonicida, A. hydrophila, Edwardsiella tarda, Vibrio parahaemolyticus, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, and methicillin-resistant S. aureus. The AMP showed promising antibacterial activity, with MIC and MBC values ranging from 0.89 to 917.1 µgmL-1 and 3.67 to 1100.52 µgmL-1, respectively. In addition, KK12YW exhibited resistance to high temperatures and remained effective even in the presence of serum and salt, indicating its stability. The peptide also demonstrated minimal hemolysis toward fish RBCs, even at higher concentrations. Taken together, these findings indicate that KK12YW could be a highly promising and viable substitute for conventional antibiotics to combat microbial infections in aquaculture.

Size-Controlled Synthesis of Gold Nanoparticles Tethering Antimicrobial Peptides with Potent Broad-Spectrum Antimicrobial and Antibiofilm Activities.

New antimicrobials are urgently needed to combat the rising global health concern of antibiotic resistance. Antimicrobial peptides (AMPs) are one of the leading candidates as new antimicrobials since they target bacterial membranes and are therefore less prone to bacterial resistance. However, poor enzymatic stability, high production costs, and toxicity are drawbacks that limit their clinical use. Conjugation of AMPs to gold nanoparticles (NPs) may help to improve enzymatic stability and, thus, their overall antimicrobial efficiency. We did a one-pot synthesis of size-controlled (10 nm) gold NPs selectively conjugated to lipopeptides and determined their antibacterial activity. The conjugates exhibited potent (0.13-1.25 µM) antimicrobial activity against clinical isolates, including Gram-positive methicillin-resistant Staphylococcus aureus (S. aureus) ATCC33593, Gram-negative Escherichia coli (E. coli) CTX-M-14, multidrug-resistant Pseudomonas aeruginosa LESB58 and Acinetobacter baumannii ATCC19606, and showed promising activity (90% inhibition of initial biofilms and 80% reduction of preformed biofilms) against S. aureus and E. coli DH5α biofilms at low micromolar concentrations. The conjugates were stable in rat serum and not toxic to representative mammalian cell lines in vitro (≤64 µM) and in vivo (≤100 µM).