Antimicrobial and Antibiofilm Peptides

Non-canonical amino acid bioincorporation into antimicrobial peptides and its challenges

The rise of antimicrobial resistance and multi-drug resistant pathogens has necessitated explorations for novel antibiotic agents as the discovery of conventional antibiotics is becoming economically less viable and technically more challenging for biopharma. Antimicrobial peptides (AMPs) have emerged as a promising alternative because of their particular mode of action, broad spectrum and difficulty that microbes have in becoming resistant to them. The AMPs bacitracin, gramicidin, polymyxins and daptomycin are currently used clinically. However, their susceptibility to proteolytic degradation, toxicity profile, and complexities in large-scale manufacture have hindered their development. To improve their proteolytic stability, methods such as integrating non-canonical amino acids (ncAAs) into their peptide sequence have been adopted, which also improves their potency and spectrum of action. The benefits of ncAA incorporation have been made possible by solid-phase peptide synthesis. However, this method is not always suitable for commercial production of AMPs because of poor yield, scale-up difficulties, and its non-'green' nature. Bioincorporation of ncAA as a method of integration is an emerging field geared towards tackling the challenges of solid-phase synthesis as a green, cheaper, and scalable alternative for commercialisation of AMPs. This review focusses on the bioincorporation of ncAAs; some challenges associated with the methods are outlined, and notes are given on how to overcome these challenges. The review focusses particularly on addressing two key challenges: AMP cytotoxicity towards microbial cell factories and the uptake of ncAAs that are unfavourable to them. Overcoming these challenges will draw us closer to a greater yield and an environmentally friendly and sustainable approach to make AMPs more druggable.

Tetrahedral framework nucleic acid-based small-molecule inhibitor delivery for ecological prevention of biofilm

Biofilm formation constitutes the primary cause of various chronic infections, such as wound infections, gastrointestinal inflammation and dental caries. While preliminary achievement of biofilm inhibition is possible, the challenge lies in the difficulty of eliminating the bactericidal effects of current drugs that lead to microbiota imbalance. This study, utilizing in vitro and in vivo models of dental caries, aims to efficiently inhibit biofilm formation without inducing bactericidal effects, even against pathogenic bacteria. The tetrahedral framework nucleic acid (tFNA) was employed as a delivery vector for a small-molecule inhibitor (smI) specifically targeting the activity of glucosyltransferases C (GtfC). It was observed that tFNA loaded smI in a small-groove binding manner, efficiently transferring it into Streptococcus mutans, thereby inhibiting GtfC activity and extracellular polymeric substances formation without compromising bacterial survival. Furthermore, smI-loaded tFNA demonstrated a reduction in the severity of dental caries in vivo without adversely affecting oral microbial diversity and exhibited desirable topical and systemic biosafety. This study emphasizes the concept of 'ecological prevention of biofilm', which is anticipated to advance the optimization of biofilm prevention strategies and the clinical application of DNA nanocarrier-based drug formulations.

Navigating Antibacterial Frontiers: A Panoramic Exploration of Antibacterial Landscapes, Resistance Mechanisms, and Emerging Therapeutic Strategies

The development of effective antibacterial solutions has become paramount in maintaining global health in this era of increasing bacterial threats and rampant antibiotic resistance. Traditional antibiotics have played a significant role in combating bacterial infections throughout history. However, the emergence of novel resistant strains necessitates constant innovation in antibacterial research. We have analyzed the data on antibacterials from the CAS Content Collection, the largest human-curated collection of published scientific knowledge, which has proven valuable for quantitative analysis of global scientific knowledge. Our analysis focuses on mining the CAS Content Collection data for recent publications (since 2012). This article aims to explore the intricate landscape of antibacterial research while reviewing the advancement from traditional antibiotics to novel and emerging antibacterial strategies. By delving into the resistance mechanisms, this paper highlights the need to find alternate strategies to address the growing concern.

Combating Antimicrobial Resistance by Employing Antimicrobial Peptides: Immunomodulators and Therapeutic Agents against Infectious Diseases

The rising prevalence of multiple-drug-resistant pathogens poses a formidable challenge to conventional antimicrobial treatments. The inability of potent antibiotics to combat these "superbugs" underscores the pressing need for alternative therapeutic agents. Antimicrobial peptides (AMPs) represent an alternative class of antibiotics. AMPs are essential immunomodulatory molecules that are found in various organisms. They play a pivotal role in managing microbial ecosystems and bolstering innate immunity by targeting and eliminating invading microorganisms. AMPs also have applications in the agriculture sector by combating animal as well as plant pathogens. AMPs can be exploited for the targeted therapy of various diseases and can also be used in drug-delivery systems. They can be used in synergy with current treatments like antibiotics and can potentially lead to a lower required dosage. AMPs also have huge potential in wound healing and regenerative medicine. Developing AMP-based strategies with improved safety, specificity, and efficacy is crucial in the battle against alarming global microbial resistance. This review will explore AMPs' increasing applicability, their mode of antimicrobial activity, and various delivery systems enhancing their stability and efficacy.

Biofilm inhibition/eradication: exploring strategies and confronting challenges in combatting biofilm

Biofilms are complex communities of microorganisms enclosed in a self-produced extracellular matrix, posing a significant threat to different sectors, including healthcare and industry. This review provides an overview of the challenges faced due to biofilm formation and different novel strategies that can combat biofilm formation. Bacteria inside the biofilm exhibit increased resistance against different antimicrobial agents, including conventional antibiotics, which can lead to severe problems in livestock and animals, including humans. In addition, biofilm formation also imposes heavy economic pressure on industries. Hence it becomes necessary to explore newer alternatives to eradicate biofilms effectively without applying selection pressure on the bacteria. Excessive usage of antibiotics may also lead to an increase in the number of resistant strains as bacteria employ an advanced antimicrobial resistance mechanism. This review provides insight into multifaceted technologies like quorum sensing inhibition, enzymes, antimicrobial peptides, bacteriophage, phytocompounds, and nanotechnology to neutralize biofilms without developing antimicrobial resistance (AMR). Furthermore, it will pave the way for developing newer therapeutic agents to deal with biofilms more efficiently.

Plumbagin inhibits fungal growth, HMGB1/LOX-1 pathway and inflammatory factors in A. fumigatus keratitis

To investigate the anti-inflammatory and antifungal effects of plumbagin (PL) in Aspergillus fumigatus (A. fumigatus) keratitis, the minimum inhibitory concentration (MIC), time-killing curve, spore adhesion, crystal violet staining, calcium fluoride white staining, and Propidium Iodide (PI) staining were employed to assess the antifungal activity of PL in vitro against A. fumigatus. The cytotoxicity of PL was assessed using the Cell Counting Kit-8 (CCK8). The impact of PL on the expression of HMGB1, LOX-1, TNF-α, IL-1β, IL-6, IL-10 and ROS in A. fumigatus keratitis was investigated using RT-PCR, ELISA, Western blot, and Reactive oxygen species (ROS) assay. The therapeutic efficacy of PL against A. fumigatus keratitis was assessed through clinical scoring, plate counting, Immunofluorescence and Hematoxylin-Eosin (HE) staining. Finally, we found that PL inhibited the growth, spore adhesion, and biofilm formation of A. fumigatus and disrupted the integrity of its cell membrane and cell wall. PL decreased IL-6, TNF-α, and IL-1β levels while increasing IL-10 expression in fungi-infected mice corneas and peritoneal macrophages. Additionally, PL significantly attenuated the HMGB1/LOX-1 pathway while reversing the promoting effect of Boxb (an HMGB1 agonist) on HMGB1/LOX-1. Moreover, PL decreased the level of ROS. In vivo, clinical scores, neutrophil recruitment, and fungal burden were all significantly reduced in infected corneas treated with PL. In summary, the inflammatory process can be inhibited by PL through the regulation of the HMGB-1/LOX-1 pathway. Simultaneously, PL can exert antifungal effects by limiting fungal spore adhesion and biofilm formation, as well as causing destruction of cell membranes and walls.

Marine Antimicrobial Peptides: An Emerging Nightmare to the Life-Threatening Pathogens

The emergence of multidrug-resistant pathogens due to improper usage of conventional antibiotics has created a global health crisis. Alternatives to antibiotics being an urgent need, the scientific community is forced to search for new antimicrobials. This exploration has led to the discovery of antimicrobial peptides, a group of small peptides occurring in different phyla such as Porifera, Cnidaria, Annelida, Arthropoda, Mollusca, Echinodermata, and Chordata, as a component of their innate immune system. The marine environment, possessing immense diversity of organisms, is undoubtedly one of the richest sources of unique potential antimicrobial peptides. The distinctiveness of marine antimicrobial peptides lies in their broad-spectrum activity, mechanism of action, less cytotoxicity, and high stability, which form the benchmark for developing a potential therapeutic. This review aims to (1) synthesise the available information on the distinctive antimicrobial peptides discovered from marine organisms, particularly over the last decade, and (2) discuss the distinctiveness of marine antimicrobial peptides and their prospects.

Antimicrobials: An update on new strategies to diversify treatment for bacterial infections

Ninety-five years after Fleming's discovery of penicillin, a bounty of antibiotic compounds have been discovered, modified, or synthesised. Diversification of target sites, improved stability and altered activity spectra have enabled continued antibiotic efficacy, but overwhelming reliance and misuse has fuelled the global spread of antimicrobial resistance (AMR). An estimated 1.27 million deaths were attributable to antibiotic resistant bacteria in 2019, representing a major threat to modern medicine. Although antibiotics remain at the heart of strategies for treatment and control of bacterial diseases, the threat of AMR has reached catastrophic proportions urgently calling for fresh innovation. The last decade has been peppered with ground-breaking developments in genome sequencing, high throughput screening technologies and machine learning. These advances have opened new doors for bioprospecting for novel antimicrobials. They have also enabled more thorough exploration of complex and polymicrobial infections and interactions with the healthy microbiome. Using models of infection that more closely resemble the infection state in vivo, we are now beginning to measure the impacts of antimicrobial therapy on host/microbiota/pathogen interactions. However new approaches are needed for developing and standardising appropriate methods to measure efficacy of novel antimicrobial combinations in these contexts. A battery of promising new antimicrobials is now in various stages of development including co-administered inhibitors, phages, nanoparticles, immunotherapy, anti-biofilm and anti-virulence agents. These novel therapeutics need multidisciplinary collaboration and new ways of thinking to bring them into large scale clinical use.

Microbial anti-biofilms: types and mechanism of action

Biofilms have been recognized as a serious threat to public health as it protects microbes from antimicrobials, immune defence mechanisms, chemical treatments and nutritional stress. Biofilms are also a source of concern in industries and water treatment because their presence compromises the integrity of equipment. To overcome these problems, it is necessary to identify novel anti-biofilm compounds. Products of microorganisms have been identified as promising broad-spectrum anti-biofilm agents. These natural products include biosurfactants, antimicrobial peptides, enzymes and bioactive compounds. Anti-biofilm products of microbial origin are chemically diverse and possess a broad spectrum of activities against biofilms. The objective of this review is to give an overview of the different types of microbial anti-biofilm products and their mechanisms of action.

Molecular Aspects of the Functioning of Pathogenic Bacteria Biofilm Based on Quorum Sensing (QS) Signal-Response System and Innovative Non-Antibiotic Strategies for Their Elimination

One of the key mechanisms enabling bacterial cells to create biofilms and regulate crucial life functions in a global and highly synchronized way is a bacterial communication system called quorum sensing (QS). QS is a bacterial cell-to-cell communication process that depends on the bacterial population density and is mediated by small signalling molecules called autoinducers (AIs). In bacteria, QS controls the biofilm formation through the global regulation of gene expression involved in the extracellular polymeric matrix (EPS) synthesis, virulence factor production, stress tolerance and metabolic adaptation. Forming biofilm is one of the crucial mechanisms of bacterial antimicrobial resistance (AMR). A common feature of human pathogens is the ability to form biofilm, which poses a serious medical issue due to their high susceptibility to traditional antibiotics. Because QS is associated with virulence and biofilm formation, there is a belief that inhibition of QS activity called quorum quenching (QQ) may provide alternative therapeutic methods for treating microbial infections. This review summarises recent progress in biofilm research, focusing on the mechanisms by which biofilms, especially those formed by pathogenic bacteria, become resistant to antibiotic treatment. Subsequently, a potential alternative approach to QS inhibition highlighting innovative non-antibiotic strategies to control AMR and biofilm formation of pathogenic bacteria has been discussed.

A potent candicidal peptide designed based on an encrypted peptide from a proteinase inhibitor

Antimicrobial peptides (AMP) represent an alternative in the treatment of fungal infections associated with countless deaths. Here, we report a new AMP, named KWI-19, which was designed based on a peptide encrypted in the sequence of an Inga laurina Kunitz-type inhibitor (ILTI). KWI-19 inhibited the growth of Candida species and acted as a fungicidal agent from 2.5 to 20 μmol L-1, also showing synergistic activity with amphotericin B. Kinetic assays showed that KWI-19 killed Candida tropicalis cells within 60 min. We also report the membrane-associated mechanisms of action of KWI-19 and its interaction with ergosterol. KWI-19 was also characterized as a potent antibiofilm peptide, with activity against C. tropicalis. Finally, non-toxicity was reported against Galleria mellonella larvae, thus strengthening the interest in all the bioactivities mentioned above. This study extends our knowledge on how AMPs can be engineered from peptides encrypted in larger proteins and their potential as candicidal agents.

Development of a novel hybrid antimicrobial peptide for enhancing antimicrobial spectrum and potency against food-borne pathogens

AIMS

To address the increasingly serious challenge of the transmission of foodbrone pathogens in the food chain.

METHODS AND RESULTS

In this study, we employed rational design strategies, including truncation, amino acid substitution, and heterozygosity, to generate seven engineered peptides with α-helical structure, cationic property, and amphipathic characteristics based on the original Abhisin template. Among them, as the hybird antimicrobial peptide (AMP), AM exhibits exceptional stability, minimal toxicity, as well as broad-spectrum and potent antimicrobial activity against foodborne pathogens. Besides, it was observed that the electrostatic incorporation demonstrates by AM results in its primary targeting and disruption of the cell wall and membrane of Escherichia coli O157: H7 (EHEC) and methicillin-resistant Staphylococcus aureus (MRSA), resulting in membrane perforation and enhanced permeability. Additionally, AM effectively counteracts the deleterious effects of lipopolysaccharide, eradicating biofilms and ultimately inducing the demise of both food spoilage and pathogenic microorganisms.

CONCLUSIONS

The findings highlight the significant potential of AM as a highly promising candidate for a novel food preservative and its great importance in the design and optimization of AMP-related agents.

Release of a novel peptide from ferritin nanocages: A new tool for therapeutic applications

The development of new drug delivery systems for targeted chemotherapy release in cancer cells represents a very promising tool. In this contest, protein-based nanocages have considerable potential as drug delivery devices. Notably, ferritin has emerged as an excellent candidate due to its unique architecture, surface properties and high biocompatibility. A promising strategy might then involve ferritin cargos for specifical release of AntiMicrobial Peptides endowed with anticancer activity to cancer cells. In this paper, we encapsulated the TRIL analogue of Temporin-L peptide within a ferritin nanocage and evaluated the cargo biological properties. The results demonstrated a reduced haemolytic activity of the peptide and a selective cytotoxicity activity on cancer cells likely mediated by oxidative stress while having no effects on non-tumoral cells. The combination of the properties of ferritin with TRIL, might open up the way to the development of novel peptide delivery systems for future pharmaceutical applications.

Fingolimod Inhibits Exopolysaccharide Production and Regulates Relevant Genes to Eliminate the Biofilm of K. pneumoniae

Klebsiella pneumoniae (K. pneumoniae) exhibits the ability to form biofilms as a means of adapting to its adverse surroundings. K. pneumoniae in this biofilm state demonstrates remarkable resistance, evades immune system attacks, and poses challenges for complete eradication, thereby complicating clinical anti-infection efforts. Moreover, the precise mechanisms governing biofilm formation and disruption remain elusive. Recent studies have discovered that fingolimod (FLD) exhibits biofilm properties against Gram-positive bacteria. Therefore, the antibiofilm properties of FLD were evaluated against multidrug-resistant (MDR) K. pneumoniae in this study. The antibiofilm activity of FLD against K. pneumoniae was assessed utilizing the Alamar Blue assay along with confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and crystal violet (CV) staining. The results showed that FLD effectively reduced biofilm formation, exopolysaccharide (EPS), motility, and bacterial abundance within K. pneumoniae biofilms without impeding its growth and metabolic activity. Furthermore, the inhibitory impact of FLD on the production of autoinducer-2 (AI-2) signaling molecules was identified, thereby demonstrating its notable anti-quorum sensing (QS) properties. The results of qRT-PCR analysis demonstrated that FLD significantly decreased the expression of genes associated with the efflux pump gene (AcrB, kexD, ketM, kdeA, and kpnE), outer membrane (OM) porin proteins (OmpK35, OmpK36), the quorum-sensing (QS) system (luxS), lipopolysaccharide (LPS) production (wzm), and EPS production (pgaA). Simultaneously, FLD exhibited evident antibacterial synergism, leading to an increased survival rate of G. mellonella infected with MDR K. pneumoniae. These findings suggested that FLD has substantial antibiofilm properties and synergistic antibacterial potential for colistin in treating K. pneumoniae infections.

Strategies for combating antibiotic resistance in bacterial biofilms

Biofilms, which are complexes of microorganisms that adhere to surfaces and secrete protective extracellular matrices, wield substantial influence across diverse domains such as medicine, industry, and environmental science. Despite ongoing challenges posed by biofilms in clinical medicine, research in this field remains dynamic and indeterminate. This article provides a contemporary assessment of biofilms and their treatment, with a focus on recent advances, to chronicle the evolving landscape of biofilm research.

Machine learning assisted rational design of antimicrobial peptides based on human endogenous proteins and their applications for cosmetic preservative system optimization

Preservatives are essential components in cosmetic products, but their safety issues have attracted widespread attention. There is an urgent need for safe and effective alternatives. Antimicrobial peptides (AMPs) are part of the innate immune system and have potent antimicrobial properties. Using machine learning-assisted rational design, we obtained a novel antibacterial peptide, IK-16-1, with significant antibacterial activity and maintaining safety based on β-defensins. IK-16-1 has broad-spectrum antimicrobial properties against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans, and has no haemolytic activity. The use of IK-16-1 holds promise in the cosmetics industry, since it can serve as a preservative synergist to reduce the amount of other preservatives in cosmetics. This study verified the feasibility of combining computational design with artificial intelligence prediction to design AMPs, achieving rapid screening and reducing development costs.

Rational Design and Antimicrobial Potency Assessment of Abaecin Analogues

The widespread and escalating emergence of multidrug resistance is now recognized as one of the most severe global threats to human health. To address the urgent issue of drug-resistant bacteria and the limitation of effective clinical treatments, antimicrobial peptides (AMPs) have been developed as promising substituents of conventional antibiotics. In this study, rational design strategies were employed to acquire seven cationic and α-helical engineered peptides based on the original template of Abaecin. After investigation, we found that AC7 (LLRRWKKLFKKIIRWPRPLPNPGH) demonstrated potent and broad-spectrum antimicrobial activity. Additionally, it demonstrated low cytotoxicity and hemolysis while maintaining good stability. Notably, AC7 displays the antibacterial mechanism with superior abilities in cell membrane disruption and potential DNA binding in vitro, as well as effectively disrupting biofilms. Moreover, the murine skin wound model infected with drug-resistant Pseudomonas aeruginosa was employed to evaluate the anti-infective efficacy and therapeutic potential of AC7. It was observed that AC7 displays a remarkable capacity to inhibit wound colonization, reduce levels of inflammatory cytokines (TNF-α) and inflammatory cells (white blood cells (WBC), monocytes (MONO), lymphocytes (LYMPH), neutrophils (GRAN)), promote the levels of IL-10 and VEGF, and enhance wound healing. Overall, these findings demonstrate the potential of AC7 as a viable alternative to traditional antibiotics.

The natriuretic peptide receptor agonist osteocrin disperses Pseudomonas aeruginosa biofilm

Biofilms are highly tolerant to antimicrobials and host immune defense, enabling pathogens to thrive in hostile environments. The diversity of microbial biofilm infections requires alternative and complex treatment strategies. In a previous work we demonstrated that the human Atrial Natriuretic Peptide (hANP) displays a strong anti-biofilm activity toward Pseudomonas aeruginosa and that the binding of hANP by the AmiC protein supports this effect. This AmiC sensor has been identified as an analog of the human natriuretic peptide receptor subtype C (h-NPRC). In the present study, we evaluated the anti-biofilm activity of the h-NPRC agonist, osteocrin (OSTN), a hormone that displays a strong affinity for the AmiC sensor at least in vitro. Using molecular docking, we identified a pocket in the AmiC sensor that OSTN reproducibly docks into, suggesting that OSTN might possess an anti-biofilm activity as well as hANP. This hypothesis was validated since we observed that OSTN dispersed established biofilm of P. aeruginosa PA14 strain at the same concentrations as hANP. However, the OSTN dispersal effect is less marked than that observed for the hANP (-61% versus -73%). We demonstrated that the co-exposure of P. aeruginosa preformed biofilm to hANP and OSTN induced a biofilm dispersion with a similar effect to that observed with hANP alone suggesting a similar mechanism of action of these two peptides. This was confirmed by the observation that OSTN anti-biofilm activity requires the activation of the complex composed by the sensor AmiC and the regulator AmiR of the ami pathway. Using a panel of both P. aeruginosa laboratory reference strains and clinical isolates, we observed that the OSTN capacity to disperse established biofilms is highly variable from one strain to another. Taken together, these results show that similarly to the hANP hormone, OSTN has a strong potential to be used as a tool to disperse P. aeruginosa biofilms.

Antimicrobial Peptides as Immunomodulators and Antimycobacterial Agents to Combat Mycobacterium tuberculosis: a Critical Review

Tuberculosis (TB) is a devastating disease foisting a significantly high morbidity, prepotent in low- and middle-income developing countries. Evolution of drug resistance among Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, has made the TB treatment more complicated. The protracted nature of present TB treatment, persistent and tolerant Mtb populations, interaction with antiretroviral therapy and existing toxicity concerned with conventional anti-TB drugs are the four major challenges inflicted with emergence of drug-resistant mycobacterial strains, and the standard medications are unable to combat these strains. These factors emphasize an exigency to develop new drugs to overcome these barriers in current TB therapy. With this regard, antimycobacterial peptides derived from various sources such as human cells, bacterial sources, mycobacteriophages, fungal, plant and animal sources could be considered as antituberculosis leads as most of these peptides are associated with dual advantages of having both bactericidal activity towards Mtb as well as immuno-regulatory property. Some of the peptides possess the additional advantage of interacting synergistically with antituberculosis medications too, thereby increasing their efficiency, underscoring the vigour of antimicrobial peptides (AMPs) as best possible alternative therapeutic candidates or adjuvants in TB treatment. Albeit the beneficiary features of these peptides, few obstacles allied with them like cytotoxicity and proteolytic degradation are matter of concerns too. In this review, we have focused on structural hallmarks, targeting mechanisms and specific structural aspects contributing to antimycobacterial activity and discovered natural and synthetic antimycobacterial peptides along with their sources, anti-TB, immuno-regulatory properties, merits and demerits and possible delivery methods of AMPs.

Influence of a D-enantiomeric peptide on the anticorrosion ability of titanium with different surface roughness against Streptococcus mutans biofilms

OBJECTIVE

To investigate the effectiveness of a d-enantiomeric antibiofilm peptide (DJK-5) on the anticorrosion ability of titanium (Ti) with different surface roughness against Streptococcus mutans biofilms.

METHODS

Commercially pure Ti disks with machined (MA, smooth) or sandblasted + acid-etched (SLA, rough) surfaces were prepared and characterized. All disks were divided into three groups: a positive control (PC) group with S. mutans, a DJK-5-treated group, and a negative control (NC) group without S. mutans. Biofilm formation and corrosion on Ti surfaces were determined by confocal laser scanning microscopy and scanning electron microscopy after 2 and 6 days, and the electrochemical properties were evaluated.

RESULTS

Ten μg/mL of DJK-5 killed 83.3 % and 87.4 % of biofilms on SLA and MA Ti surfaces, respectively after 2 days, and 72.9 % and 77.7 % after 6 days, with more bacteria surviving on SLA surfaces with higher roughness (p < 0.05). DJK-5 treatment induced less surface defects with tiny pit corrosion than PC. DJK-5 treatment when compared to PC, led to electrochemical properties more reflecting NC surfaces, including significantly less negative corrosion potential, lower corrosion current, and higher passive film resistance (p < 0.05). SLA surfaces exhibited higher current density and lower resistance than MA surfaces (p < 0.05).

CONCLUSION

DJK-5 effectively enhanced the corrosion resistance of Ti with different surface roughness while killing S. mutans biofilms, and smooth surfaces were more susceptible to peptide treatment.

CLINICAL SIGNIFICANCE

The antibiofilm peptide is promising for promoting the anticorrosion ability of Ti against biofilms, thereby preventing biofilm-related infections.

Application of coliphage as biocontrol agent in combination with gamma irradiation to eliminate multi-drug-resistant E. coli in minimally processed vegetables

Biofilm formation is a rising concern in the food industry. Escherichia coli (E. coli) is one of the most important food-borne pathogens that can survive in food and food-related environments and eventually produce biofilms. This study suggested that both coliphages used were successful in preventing the creation of new biofilms as well as removing existing ones. Confocal laser scanning microscopy verified these findings. According to the findings, neither coliphage survived at 37 °C, but both remained stable at 4 °C and - 20 °C for extended periods of time. The study revealed that both coliphages demonstrated a greater degree of gamma irradiation resistance when compared to E. coli. The study's results indicate that the implementation of a dual method, which incorporates gamma irradiation (1.5 kGy) and coliphage treatment, on various kinds of vegetables that were infected with E. coli, resulted in a significant reduction in bacterial count (surpassing 99.99%) following a 24-h incubation period. Combining gamma irradiation and the coliphage approach was significantly effective at lowering polysaccharide concentrations and proteins in the biofilm matrix. The results revealed that the pairing of gamma irradiation and coliphages acted in conjunction to cause disruptions in the matrix of biofilm, thereby promoting cell removal compared with either of the individual treatments. Ca+ ions strengthen the weak virion interaction with the relevant bacterial host cell receptors during the adsorption process. In conclusion, use of coliphage in combination with gamma irradiation treatment can be applied to improve fresh produce's microbial safety and enhance its storability in supermarkets.

Confronting the Threat: Designing Highly Effective bis-Benzimidazolium Agents to Overcome Biofilm Persistence and Antimicrobial Resistance

The objective of this study is to take the initial steps toward developing novel antibiotics to counteract the escalating problem of antimicrobial and bacterial persistence, particularly in relation to biofilms. Our approach involves emulating the structural characteristics of cationic antimicrobial peptides. To circumvent resistance development, we have designed a library of bis-benzimidazolium salts that selectively target the microbial membranes in a nonspecific manner. To explore their structure-activity relationship, we conducted experiments using these compounds on various pathogens known for their resistance to conventional antibiotics, including Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), and Gram-negative Escherichia coli (E. coli). Notably, two bis-benzimidazolium salts exhibited robust antimicrobial activity while maintaining a high level of selectivity compared with mammalian cells. Our investigations revealed significant antibiofilm activity, as these compounds rapidly acted against established biofilms. In addition, bis-benzimidazolium compounds exhibited consistent results in resistance development and cross-resistance studies. Consequently, amphiphilic bis-benzimidazolium salts hold promise as potential candidates to combat resistance-associated infections.

Plant-derived rennet: research progress, novel strategies for their isolation, identification, mechanism, bioactive peptide generation, and application in cheese manufacturing

Rennet, an aspartate protease found in the stomach of unweaned calves, effectively cuts the peptide bond between Phe105-Met106 in κ-casein, hydrolyzing the casein micelles to coagulate the milk and is a crucial additive in cheese production. Rennet is one of the most used enzymes of animal origin in cheese making. However, using rennet al.one is insufficient to meet the increasing demand for cheese production worldwide. Numerous studies have shown that plant rennet can be an alternative to bovine rennet and exhibit a good renneting effect. Therefore, it is crucial and urgent to find a reliable plant rennet. Based on our team's research on rennet enzymes of plant origin, such as from Dregea sinensis Hemsl. and Moringa oleifer Lam., for more than ten years, this paper reviews the relevant literature on rennet sources, isolation, identification, rennet mechanism, functional active peptide screening, and application in cheese production. In addition, it proposes the various techniques for targeted isolation and identification of rennet and efficient screening of functionally active peptides, which show excellent prospects for development.

The Antimicrobial, Antibiofilm and Anti-Inflammatory Activities of P13#1, a Cathelicidin-like Achiral Peptoid

Cationic antimicrobial peptides (CAMPs) are powerful molecules with antimicrobial, antibiofilm and endotoxin-scavenging activities. These properties make CAMPs very attractive drugs in the face of the rapid increase in multidrug-resistant (MDR) pathogens, but they are limited by their susceptibility to proteolytic degradation. An intriguing solution to this issue could be the development of functional mimics of CAMPs with structures that enable the evasion of proteases. Peptoids (N-substituted glycine oligomers) are an important class of peptidomimetics with interesting benefits: easy synthetic access, intrinsic proteolytic stability and promising bioactivities. Here, we report the characterization of P13#1, a 13-residue peptoid specifically designed to mimic cathelicidins, the best-known and most widespread family of CAMPs. P13#1 showed all the biological activities typically associated with cathelicidins: bactericidal activity over a wide spectrum of strains, including several ESKAPE pathogens; the ability to act in combination with different classes of conventional antibiotics; antibiofilm activity against preformed biofilms of Pseudomonas aeruginosa, comparable to that of human cathelicidin LL-37; limited toxicity; and an ability to inhibit LPS-induced proinflammatory effects which is comparable to that of "the last resource" antibiotic colistin. We further studied the interaction of P13#1 with SDS, LPSs and bacterial cells by using a fluorescent version of P13#1. Finally, in a subcutaneous infection mouse model, it showed antimicrobial and anti-inflammatory activities comparable to ampicillin and gentamicin without apparent toxicity. The collected data indicate that P13#1 is an excellent candidate for the formulation of new antimicrobial therapies.

Novel cationic cryptides in Penaeus vannamei demonstrate antimicrobial and anti-cancer activities

Cryptides are a subfamily of bioactive peptides that exist in all living organisms. They are latently encrypted in their parent sequences and exhibit a wide range of biological activities when decrypted via in vivo or in vitro proteases. Cationic cryptides tend to be drawn to the negatively charged membranes of microbial and cancer cells, causing cell death through various mechanisms. This makes them promising candidates for alternative antimicrobial and anti-cancer therapies, as their mechanism of action is independent of gene mutations. In the current study, we employed an in silico approach to identify novel cationic cryptides with potential antimicrobial and anti-cancer activities in atypical and systematic strategy by reanalysis of a publicly available RNA-seq dataset of Pacific white shrimp (Penaus vannamei) in response to bacterial infection. Out of 12 cryptides identified, five were selected based on their net charges and potential for cell penetration. Following chemical synthesis, the cryptides were assayed in vitro to test for their biological activities. All five cryptides demonstrated a wide range of selective activity against the tested microbial and cancer cells, their anti-biofilm activities against mature biofilms, and their ability to interact with Gram-positive and negative bacterial membranes. Our research provides a framework for a comprehensive analysis of transcriptomes in various organisms to uncover novel bioactive cationic cryptides. This represents a significant step forward in combating the crisis of multi-drug-resistant microbial and cancer cells, as these cryptides neither induce mutations nor are influenced by mutations in the cells they target.

Antibacterial activities of anthraquinones: structure-activity relationships and action mechanisms

With the increasing prevalence of untreatable infections caused by antibiotic-resistant bacteria, the discovery of new drugs from natural products has become a hot research topic. The antibacterial activity of anthraquinones widely distributed in traditional Chinese medicine has attracted much attention. Herein, the structure and activity relationships (SARs) of anthraquinones as bacteriostatic agents are reviewed and elucidated. The substituents of anthraquinone and its derivatives are closely related to their antibacterial activities. The stronger the polarity of anthraquinone substituents is, the more potent the antibacterial effects appear. The presence of hydroxyl groups is not necessary for the antibacterial activity of hydroxyanthraquinone derivatives. Substitution of di-isopentenyl groups can improve the antibacterial activity of anthraquinone derivatives. The rigid plane structure of anthraquinone lowers its water solubility and results in the reduced activity. Meanwhile, the antibacterial mechanisms of anthraquinone and its analogs are explored, mainly including biofilm formation inhibition, destruction of the cell wall, endotoxin inhibition, inhibition of nucleic acid and protein synthesis, and blockage of energy metabolism and other substances.

The effect of metalation on antimicrobial piscidins imbedded in normal and oxidized lipid bilayers

Metalation of the N-terminal Amino Terminal Cu(ii)- and Ni(ii)-binding (ATCUN) motif may enhance the antimicrobial properties of piscidins. Molecular dynamics simulations of free and nickelated piscidins 1 and 3 (P1 and P3) were performed in 3 : 1 POPC/POPG and 2.6 : 1 : 0.4 POPC/POPG/aldo-PC bilayers (POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine: POPG, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol; aldo-PC, 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphocholine) bilayer models. Nickel(ii) binding decreases the conformation dynamics of the ATCUN motif and lowers the charge of the N-terminus to allow it to embed deeper in the bilayer without significantly changing the overall depth due to interactions of the charged half-helix of the peptide with the headgroups. Phe1⋯Ni2+ cation-π and Phe2-Phe1 CH-π interactions contribute to a small fraction of structures within the nickelated P1 simulations and may partially protect a bound metal from metal-centered chemical activity. The substitution of Phe2 for Ile2 in P3 sterically blocks conformations with cation-π interactions offering less protection to the metal. This difference between metalated P1 and P3 may indicate a mechanism by which peptide sequence can influence antimicrobial properties. Any loss of bilayer integrity due to chain reversal of the oxidized phospholipid chains of aldo-PC may be enhanced in the presence of metalated piscidins.

Microbial Biofilms: Applications, Clinical Consequences, and Alternative Therapies

Biofilms are complex communities of microorganisms that grow on surfaces and are embedded in a matrix of extracellular polymeric substances. These are prevalent in various natural and man-made environments, ranging from industrial settings to medical devices, where they can have both positive and negative impacts. This review explores the diverse applications of microbial biofilms, their clinical consequences, and alternative therapies targeting these resilient structures. We have discussed beneficial applications of microbial biofilms, including their role in wastewater treatment, bioremediation, food industries, agriculture, and biotechnology. Additionally, we have highlighted the mechanisms of biofilm formation and clinical consequences of biofilms in the context of human health. We have also focused on the association of biofilms with antibiotic resistance, chronic infections, and medical device-related infections. To overcome these challenges, alternative therapeutic strategies are explored. The review examines the potential of various antimicrobial agents, such as antimicrobial peptides, quorum-sensing inhibitors, phytoextracts, and nanoparticles, in targeting biofilms. Furthermore, we highlight the future directions for research in this area and the potential of phytotherapy for the prevention and treatment of biofilm-related infections in clinical settings.

Alternate Antimicrobial Therapies and Their Companion Tests

New antimicrobial approaches are essential to counter antimicrobial resistance. The drug development pipeline is exhausted with the emergence of resistance, resulting in unsuccessful trials. The lack of an effective drug developed from the conventional drug portfolio has mandated the introspection into the list of potentially effective unconventional alternate antimicrobial molecules. Alternate therapies with clinically explicable forms include monoclonal antibodies, antimicrobial peptides, aptamers, and phages. Clinical diagnostics optimize the drug delivery. In the era of diagnostic-based applications, it is logical to draw diagnostic-based treatment for infectious diseases. Selection criteria of alternate therapeutics in infectious diseases include detection, monitoring of response, and resistance mechanism identification. Integrating these diagnostic applications is disruptive to the traditional therapeutic development. The challenges and mitigation methods need to be noted. Applying the goals of clinical pharmacokinetics that include enhancing efficacy and decreasing toxicity of drug therapy, this review analyses the strong correlation of alternate antimicrobial therapeutics in infectious diseases. The relationship between drug concentration and the resulting effect defined by the pharmacodynamic parameters are also analyzed. This review analyzes the perspectives of aligning diagnostic initiatives with the use of alternate therapeutics, with a particular focus on companion diagnostic applications in infectious diseases.

Green fabrication of chitosan nanoparticles using Lavendula angustifolia, optimization, characterization and in‑vitro antibiofilm activity

Chitosan nanoparticles (CNPs) are promising polymeric nanoparticles with exceptional physicochemical, antimicrobial and biological characteristics. The CNPs are preferred for a wide range of applications in the food industry, cosmetics, agriculture, medical, and pharmaceutical fields due to their biocompatibility, biodegradability, eco-friendliness, and non-toxicity. In the current study, a biologically based approach was used to biofabricate CNPs using an aqueous extract of Lavendula angustifolia leaves as a reducing agent. The TEM images show that the CNPs were spherical in shape and ranged in size from 7.24 to 9.77 nm. FTIR analysis revealed the presence of several functional groups, including C-H, C-O, CONH₂, NH₂, C-OH and C-O-C. The crystalline nature of CNPs is demonstrated by X-ray diffraction. The thermogravimetric analysis revealed that CNPs are thermally stable. The CNPs' surface is positively charged and has a Zeta potential of 10 mV. For optimising CNPs biofabrication, a face-centered central composite design (FCCCD) with 50 experiments was used. The artificial intelligence-based approach was used to analyse, validate, and predict CNPs biofabrication. The optimal conditions for maximum CNPs biofabrication were theoretically determined using the desirability function and experimentally verified. The optimal conditions that maximize CNPs biofabrication (10.11 mg/mL) were determined to be chitosan concentration 0.5%, leaves extract 75%, and initial pH 4.24. The antibiofilm activity of CNPs was evaluated in‑vitro. The results show that 1500 μg/mL of CNPs suppressed P. aeruginosa, S. aureus and C. albicans biofilm formation by 91.83 ± 1.71%, 55.47 ± 2.12% and 66.4 ± 1.76%; respectively. The promising results of the current study in biofilm inhibition by necrotizing biofilm architecture, reducing its significant constituents and inhibiting microbial cell proliferation encourage their use as natural biosafe and biocompatible anti-adherent coating in antibiofouling membranes, medical bandage/tissues and food packaging materials.

New Strategies to Kill Metabolically-Dormant Cells Directly Bypassing the Need for Active Cellular Processes

Antibiotic therapy failure is often caused by the presence of persister cells, which are metabolically-dormant bacteria capable of surviving exposure to antimicrobials. Under favorable conditions, persisters can resume growth leading to recurrent infections. Moreover, several studies have indicated that persisters may promote the evolution of antimicrobial resistance and facilitate the selection of specific resistant mutants; therefore, in light of the increasing numbers of multidrug-resistant infections worldwide, developing efficient strategies against dormant cells is of paramount importance. In this review, we present and discuss the efficacy of various agents whose antimicrobial activity is independent of the metabolic status of the bacteria as they target cell envelope structures. Since the biofilm-environment is favorable for the formation of dormant subpopulations, anti-persister strategies should also include agents that destroy the biofilm matrix or inhibit biofilm development. This article reviews examples of selected cell wall hydrolases, polysaccharide depolymerases and antimicrobial peptides. Their combination with standard antibiotics seems to be the most promising approach in combating persistent infections.

AMPFinder: A computational model to identify antimicrobial peptides and their functions based on sequence-derived information

Antimicrobial peptides (AMPs) called host defense peptides have existed among all classes of life with 5-100 amino acids generally and can kill mycobacteria, envelop viruses, bacteria, fungi, cancerous cells and so on. Owing to the non-drug resistance of AMP, it has been a wonderful agent to find novel therapies. Therefore, it is urgent to identify AMPs and predict their function in a high-throughput way. In this paper, we propose a cascaded computational model to identify AMPs and their functional type based on sequence-derived and life language embedding, called AMPFinder. Compared with other state-of-the-art methods, AMPFinder obtains higher performance both on AMP identification and AMP function prediction. AMPFinder shows better performance with improvement of F1-score (1.45%-6.13%), MCC (2.92%-12.86%) and AUC (5.13%-8.56%) and AP (9.20%-21.07%) on an independent test dataset. And AMPFinder achieve lower bias of R² on a public dataset by 10-fold cross-validation with an improvement of (18.82%-19.46%). The comparison with other state-of-the-art methods shows that AMP can accurately identify AMP and its function types. The datasets, source code and user-friendly application are available at https://github.com/abcair/AMPFinder.

Impact of the host microbiota on fungal infections: new possibilities for intervention?

Many human fungal pathogens are opportunistic. They are primarily benign residents of the human body and only become infectious when the host's immunity and microbiome are compromised. Bacteria dominate the human microbiome, playing an essential role in keeping fungi harmless and acting as the first line of defense against fungal infection. The Human Microbiome Project, launched by NIH in 2007, has stimulated extensive investigation and significantly advanced our understanding of the molecular mechanisms governing the interaction between bacteria and fungi, providing valuable insights for developing future antifungal strategies by exploiting the interaction. This review summarizes recent progress in this field and discusses new possibilities and challenges. We must seize the opportunities presented by researching bacterial-fungal interplay in the human microbiome to address the global spread of drug-resistant fungal pathogens and the drying pipelines of effective antifungal drugs.

Implant-associated biofilm infection established in an experimental Galleria mellonella model

The study reports in vivo biofilm infection implemented in an insect model. We mimicked implant-associated biofilm infections in Galleria mellonella larvae using toothbrush bristles and methicillin-resistant Staphylococcus aureus (MRSA). In vivo biofilm formation on bristle was achieved by sequentially injecting a bristle and MRSA into the larval hemocoel. It was found that biofilm formation was in progress without any external sign of infection in most of the bristle-bearing larvae for 12 h after MRSA inoculation. Whereas the activation of the prophenoloxidase system did not affect the preformed in vitro MRSA biofilms, an antimicrobial peptide interfered with in vivo biofilm formation when injected into bristle-bearing larvae infected with MRSA. Finally, our confocal laser scanning microscopic analysis revealed that the biomass of the in vivo biofilm is greater compared to that of the in vitro biofilm and harbors a distribution of dead cells, which might be bacteria and/or host cells.

Deciphering anti-biofilm property of Arthrospira platensis-origin peptides against Staphylococcusaureus

Arthrospira platensis is a valuable natural health supplement consisting of various types of vitamins, dietary minerals, and antioxidants. Although different studies have been conducted to explore the hidden benefits of this bacterium, its antimicrobial property has been poorly understood. To decipher this important feature, here, we extended our recently introduced optimization algorithm (Trader) for aligning amino acid sequences associated with the antimicrobial peptides (AMPs) of Staphylococcus aureus and A.platensis. As a result, similar amino acid sequences were identified, and several candidate peptides were generated accordingly. The obtained peptides were then filtered based on their potential biochemical and biophysical properties, and their 3D structures were simulated based on homology modeling techniques. Next, to investigate how the generated peptides can interact with S. aureus proteins (i.e., heptameric state of the hly and homodimeric form of the arsB), molecular docking approaches were used. The results indicated that four peptides included better molecular interactions relative to the other generated ones in terms of the number/average length of hydrogen bonds and hydrophobic interactions. Based on the outcomes, it can be concluded that the antimicrobial property of A.platensis might be associated with its capability in disturbing the membrane of pathogens and their functions.

Complex Networks Analyses of Antibiofilm Peptides: An Emerging Tool for Next-Generation Antimicrobials' Discovery

Microbial biofilms cause several environmental and industrial issues, even affecting human health. Although they have long represented a threat due to their resistance to antibiotics, there are currently no approved antibiofilm agents for clinical treatments. The multi-functionality of antimicrobial peptides (AMPs), including their antibiofilm activity and their potential to target multiple microbes, has motivated the synthesis of AMPs and their relatives for developing antibiofilm agents for clinical purposes. Antibiofilm peptides (ABFPs) have been organized in databases that have allowed the building of prediction tools which have assisted in the discovery/design of new antibiofilm agents. However, the complex network approach has not yet been explored as an assistant tool for this aim. Herein, a kind of similarity network called the half-space proximal network (HSPN) is applied to represent/analyze the chemical space of ABFPs, aiming to identify privileged scaffolds for the development of next-generation antimicrobials that are able to target both planktonic and biofilm microbial forms. Such analyses also considered the metadata associated with the ABFPs, such as origin, other activities, targets, etc., in which the relationships were projected by multilayer networks called metadata networks (METNs). From the complex networks' mining, a reduced but informative set of 66 ABFPs was extracted, representing the original antibiofilm space. This subset contained the most central to atypical ABFPs, some of them having the desired properties for developing next-generation antimicrobials. Therefore, this subset is advisable for assisting the search for/design of both new antibiofilms and antimicrobial agents. The provided ABFP motifs list, discovered within the HSPN communities, is also useful for the same purpose.

Collagen hydrogel with multiple antimicrobial mechanisms as anti-bacterial wound dressing

Wound infection by multidrug-resistant bacteria seriously threatens human life. Chronic wounds, with necrosis, persistent inflammation, and covered by hypoxic tissue, seriously hinder anti-infection treatments. Herein, we have developed a multifunctional hydrogel dressing with antibacterial activity in the hypoxia environment to promote wound healing. The hydrogel comprises Cypate-conjugated antimicrobial peptides (AMP-Cypates), liposome-encapsulated perfluorodecalin, and recombinant type III collagen. AMP-Cypates exhibited outstanding antibacterial activity, jointly achieved through antimicrobial peptide (AMP) activity, photothermal therapy (PTT), and photodynamic therapy (PDT). The perfluorodecalin liposomes act as the oxygen carrier to mitigate wound hypoxia condition and enhance the efficacy of PDT. The recombinant type III collagen in the hydrogel further promoted the healing of the wounds together with the eradication of bacterial infection. Taken together, the hydrogel dressing provides a platform for integrating multiple antimicrobial mechanisms for the rapid removal of bacterial infection and the healing of chronic wounds.

Prediction and bioactivity of small-molecule antimicrobial peptides from Protaetia brevitarsis Lewis larvae

Antimicrobial peptides (AMPs) are widely recognized as promising natural antimicrobial agents. Insects, as the group of animals with the largest population, have great potential as a source of AMPs. Thus, it is worthwhile to investigate potential novel AMPs from Protaetia brevitarsis Lewis larvae, which is a saprophagous pest prevalent in China. In this study, comparing the whole-genome sequence of Protaetia brevitarsis Lewis larvae with the Antimicrobial Peptide Database (APD3) led to the identification of nine peptide templates that were potentially AMPs. Next, based on the peptide templates, 16 truncated sequences were predicted to the AMPs by bioinformatics software and then underwent structural and physicochemical property analysis. Thereafter, candidate small-molecule AMPs were artificially synthesized and their minimal inhibitory concentration (MIC) values were assessed. A candidate peptide, designated FD10, exhibited strong antimicrobial activity against both bacteria and fungi comprising Escherichia coli (MIC: 8 μg/mL), Pseudomonas aeruginosa (MIC: 8 μg/mL), Bacillus thuringiensis (MIC: 8 μg/mL), Staphylococcus aureus (MIC: 16 μg/mL), and Candida albicans (MIC: 16 μg/mL). Additionally, two other candidate peptides, designated FD12 and FD15, exhibited antimicrobial activity against both E. coli (MIC: both 32 μg/mL) and S. aureus (MIC: both 16 μg/mL). Moreover, FD10, FD12, and FD15 killed almost all E. coli and S. aureus cells within 1 h, and the hemolytic effect of FD10 (0.31%) and FD12 (0.40%) was lower than that of ampicillin (0.52%). These findings indicate that FD12, FD15, and especially FD10 are promising AMPs for therapeutic application. This study promoted the development of antibacterial drugs and provided a theoretical basis for promoting the practical application of antimicrobial peptides in the Protaetia brevitarsis Lewis larvae.

Artificial intelligence-based optimization for chitosan nanoparticles biosynthesis, characterization and in‑vitro assessment of its anti-biofilm potentiality

Chitosan nanoparticles (CNPs) are promising biopolymeric nanoparticles with excellent physicochemical, antimicrobial, and biological properties. CNPs have a wide range of applications due to their unique characteristics, including plant growth promotion and protection, drug delivery, antimicrobials, and encapsulation. The current study describes an alternative, biologically-based strategy for CNPs biosynthesis using Olea europaea leaves extract. Face centered central composite design (FCCCD), with 50 experiments was used for optimization of CNPs biosynthesis. The artificial neural network (ANN) was employed for analyzing, validating, and predicting CNPs biosynthesis using Olea europaea leaves extract. Using the desirability function, the optimum conditions for maximum CNPs biosynthesis were determined theoretically and verified experimentally. The highest experimental yield of CNPs (21.15 mg CNPs/mL) was obtained using chitosan solution of 1%, leaves extract solution of 100%, initial pH 4.47, and incubation time of 60 min at 53.83°C. The SEM and TEM images revealed that CNPs had a spherical form and varied in size between 6.91 and 11.14 nm. X-ray diffraction demonstrates the crystalline nature of CNPs. The surface of the CNPs is positively charged, having a Zeta potential of 33.1 mV. FTIR analysis revealed various functional groups including C-H, C-O, CONH2, NH2, C-OH and C-O-C. The thermogravimetric investigation indicated that CNPs are thermally stable. The CNPs were able to suppress biofilm formation by P. aeruginosa, S. aureus and C. albicans at concentrations ranging from 10 to 1500 µg/mL in a dose-dependent manner. Inhibition of biofilm formation was associated with suppression of metabolic activity, protein/exopolysaccharide moieties, and hydrophobicity of biofilm encased cells (r ˃ 0.9, P = 0.00). Due to their small size, in the range of 6.91 to 11.14 nm, CNPs produced using Olea europaea leaves extract are promising for applications in the medical and pharmaceutical industries, in addition to their potential application in controlling multidrug-resistant microorganisms, especially those associated with post COVID-19 pneumonia in immunosuppressed patients.

Antibacterial peptides-loaded bioactive materials for the treatment of bone infection

Bacterial bone infection in open fractures is an urgent problem to solve in orthopedics. Antimicrobial peptides (AMPs), as a part of innate immune defense, have good biocompatibility. Their antibacterial mechanism and therapeutic application against bacteria have been widely studied. Compared with traditional antibiotics, AMPs do not easily cause bacterial resistance and can be a reliable substitute for antibiotics in the future. Therefore, various physical and chemical strategies have been developed for the combined application of AMPs and bioactive materials to infected sites, which are conducive to maintaining the local stability of AMPs, reducing many complications, and facilitating bone infection resolution. This review explored the molecular structure, function, and direct and indirect antibacterial mechanisms of AMPs, introduced two important AMPs (LL-37 and β-defensins) in bone tissues, and reviewed advanced AMP loading strategies and different bioactive materials. Finally, the latest progress and future development of AMPs-loaded bioactive materials for the promotion of bone infection repair were discussed. This study provided a theoretical basis and application strategy for the treatment of bone infection with AMP-loaded bioactive materials.

Antibacterial and anti-biofilm properties of carvacrol alone and in combination with cefixime against Escherichia coli

BACKGROUND

Plant-derived compounds can be used as antimicrobial agents in medicines and as food preservatives. These compounds can be applied along with other antimicrobial agents to strengthen the effect and/or reduce the required treatment dose.

RESULTS

In the present study, the antibacterial, anti-biofilm and quorum sensing inhibitory activity of carvacrol alone and in combination with the antibiotic cefixime against Escherichia coli was investigated. The MIC and MBC values for carvacrol were 250 μg/mL. In the checkerboard test, carvacrol showed a synergistic interaction with cefixime against E. coli (FIC index = 0.5). Carvacrol and cefixime significantly inhibited biofilm formation at MIC/2 (125 and 62.5 μg/mL), MIC/4 (62.5 and 31.25 μg/mL) and MIC/8 (31.25 and 15.625 μg/mL) for carvacrol and cefixime, respectively. The antibacterial and anti-biofilm potential effect of carvacrol confirmed by the scanning electron microscopy. Real-time quantitative reverse transcription PCR revealed significant down-regulation of the luxS and pfs genes following treatment with a MIC/2 (125 μg/mL) concentration of carvacrol alone and of only pfs gene following treatment with MIC/2 of carvacrol in combination with MIC/2 of cefixime (p < 0.05).

CONCLUSIONS

Because of the significant antibacterial and anti-biofilm activity of carvacrol, the present study examines this agent as an antibacterial drug of natural origin. The results indicate that in this study the best antibacterial and anti-biofilm properties are for the combined use of cefixime and carvacrol.

Effects of Four Antibiotics on Pseudomonas aeruginosa Motility, Biofilm Formation, and Biofilm-Specific Antibiotic Resistance Genes Expression

The aim of this study was to determine the effects of 4 antibiotics (tobramycin, fosfomycin, ciprofloxacin, and piperacillin/tazobactam) against Pseudomonas aeruginosa motility, biofilm formation, and biofilm resistance gene expression changes using different methods including microscopy, microdilution, crystal violet staining, and qRT-PCR. Although the antibiotics reduced swarming motility, they inhibited biofilm formation to a greater extent than the minimum inhibitory concentration (MIC) value. The qRT-PCR results showed that the antibiotics, other than fosfomycin, decreased the expression levels of the selected biofilm resistance genes (ndvB, tssC1, PA5033 and PA2070) in the biofilm structure compared to planktonic cells. Furthermore, it was found that there was an increase in the expression levels of biofilm resistance genes in the antibiotic application groups compared to the biofilm structure that was not treated with antibiotics. These results showed for the first time that the treatment of antibiotics at sub-MIC concentrations increases the expression levels of biofilm-specific resistance genes and contributes to resistance and motility.

Natural Medicine a Promising Candidate in Combating Microbial Biofilm

Studies on biofilm-related infections are gaining prominence owing to their involvement in most clinical infections and seriously threatening global public health. A biofilm is a natural form of bacterial growth ubiquitous in ecological niches, considered to be a generic survival mechanism adopted by both pathogenic and non-pathogenic microorganisms and entailing heterogeneous cell development within the matrix. In the ecological niche, quorum sensing is a communication channel that is crucial to developing biofilms. Biofilm formation leads to increased resistance to unfavourable ecological effects, comprising resistance to antibiotics and antimicrobial agents. Biofilms are frequently combated with modern conventional medicines such as antibiotics, but at present, they are considered inadequate for the treatment of multi-drug resistance; therefore, it is vital to discover some new antimicrobial agents that can prevent the production and growth of biofilm, in addition to minimizing the side effects of such therapies. In the search for some alternative and safe therapies, natural plant-derived phytomedicines are gaining popularity among the research community. Phytomedicines are natural agents derived from natural plants. These plant-derived agents may include flavonoids, terpenoids, lectins, alkaloids, polypeptides, polyacetylenes, phenolics, and essential oils. Since they are natural agents, they cause minimal side effects, so could be administered with dose flexibility. It is vital to discover some new antimicrobial agents that can control the production and growth of biofilms. This review summarizes and analyzes the efficacy characteristics and corresponding mechanisms of natural-product-based antibiofilm agents, i.e., phytochemicals, biosurfactants, antimicrobial peptides, and their sources, along with their mechanism, quorum sensing signalling pathways, disrupting extracellular matrix adhesion. The review also provides some other strategies to inhibit biofilm-related illness. The prepared list of newly discovered natural antibiofilm agents could help in devising novel strategies for biofilm-associated infections.

Antimicrobial Resistance and Recent Alternatives to Antibiotics for the Control of Bacterial Pathogens with an Emphasis on Foodborne Pathogens

Antimicrobial resistance (AMR) is one of the most important global public health problems. The imprudent use of antibiotics in humans and animals has resulted in the emergence of antibiotic-resistant bacteria. The dissemination of these strains and their resistant determinants could endanger antibiotic efficacy. Therefore, there is an urgent need to identify and develop novel strategies to combat antibiotic resistance. This review provides insights into the evolution and the mechanisms of AMR. Additionally, it discusses alternative approaches that might be used to control AMR, including probiotics, prebiotics, antimicrobial peptides, small molecules, organic acids, essential oils, bacteriophage, fecal transplants, and nanoparticles.

Advances in Research on Titanium and Titanium Alloys with Antibacterial Functionality for Medical Use—A Review

Materials based on titanium and its alloys are widely used in the medical and dental fields because of their excellent physical properties such as hardness, ductility and elastic modulus, etc. However, because commonly used titanium alloy internal plants do not have antibacterial properties, when these implants are implanted into the human body, there is a certain risk of infection. Such infections are extremely painful for the patient and problematic for the attending physician. In the past, infections of implants were usually treated with systemic antibiotics in combination with thorough debridement or implant replacement. However, these are passive treatments and typically cause huge physical and economic burdens on the patient. Therefore, attempts towards the development of implants with antibacterial functionality have been increasing, with the combination of titanium alloys with antibiotics, antibacterialmetals, and antibacterial peptides being the main research direction. Therefore, this paper will discuss the latest research progress in the preparation of titanium alloys with antibacterial strategies such as combining antibiotics or antimicrobial peptides, adding antimicrobial metals, and the antibacterial properties and biocompatibility of proposed systems are summarised and discussed herein. This review should serve as a reference for further research on antibacterial titanium alloy implants.

Synergistic effect and antibiofilm activity of the antimicrobial peptide K11 with conventional antibiotics against multidrug-resistant and extensively drug-resistant Klebsiella pneumoniae

Introduction

Infections caused by drug-resistant Klebsiella pneumoniae are now a serious problem for public health, associated with high morbidity and mortality due to limited treatment options. Therefore, new antibacterial agents or a combination of agents as the first line of treatment are urgently needed. K11 is a novel antimicrobial peptide (AMP) that has demonstrated in vitro antimicrobial activity against several types of bacteria. Additionally, K11 has previously shown no hemolytic activity. Herein, the antibacterial activity, the synergistic action of K11 in combination with different conventional antibiotics and the antibiofilm activity of K11 against multidrug-resistant (MDR) and extensively drug-resistant (XDR) K. pneumoniae were investigated. Meanwhile, the stability and ability to induce the bacterial resistance of K11 were also tested.

Methods

Fifteen clinical isolates of MDR/XDR K. pneumoniae were used in this study. The minimum inhibitory concentration (MIC) of K11 against these isolates was determined by the broth microdilution method. In vitro synergy between K11 and antibiotics was evaluated using the checkerboard methodology. The antibiofilm activity of K11 against K. pneumoniae strong biofilm producers were explored by the crystal violet staining. The stability in different environments and resistance induction of K11 were evaluated by MIC determination.

Results

The MIC values of K11 against MDR/XDR K. pneumoniae isolates were 8-512 μg/mL. Intriguingly, the synergistic effects were clearly observed for K11 in combination with chloramphenicol, meropenem, rifampicin, or ceftazidime, whereas no synergy was observed when K11 was combined with colistin. Besides, K11 effectively prevented biofilm formation against K. pneumoniae strong biofilm producers in a concentration-dependent manner starting at 0.25×MIC and exerted an enhancing effect when administered in combination with meropenem, chloramphenicol, or rifampicin. Additionally, K11 demonstrated high thermal and wide pH stability along with good stability in serum and physiological salts. Significantly, K. pneumoniae showed no induction of resistance even after prolonged exposure to a sub-inhibitory concentration of K11.

Conclusion

These findings indicate that K11 is a promising candidate with potent antibacterial and antibiofilm activities without inducing resistance and acts synergistically with conventional antibiotics against drug-resistant K. pneumoniae.

Effects of Conjugation of Ferrocene and Gallic Acid On desCys11/Lys12/Lys13-(p-BthTX-I)2K Peptide: Structure, Permeabilization and Antibacterial Activity

BACKGROUND

Antimicrobial resistance is an emerging global health challenge that has led researchers to study alternatives to conventional antibiotics. A promising alternative is antimicrobial peptides (AMPs), produced as the first line of defense by almost all living organisms. To improve its biological activity, the conjugation of AMPs is a promising approach.

OBJECTIVE

In this study, we evaluated the N-terminal conjugation of p-Bt (a peptide derived from Bothrops Jararacuçu`s venom) with ferrocene (Fc) and gallic acid (GA). Acetylated and linear versions of p-Bt were also synthesized to evaluate the importance of N-terminal charge and dimeric structure.

METHODS

The compounds were obtained using solid-phase peptide synthesis. Circular dichroism, vesicle permeabilization, antimicrobial activity, and cytotoxicity studies were conducted.

RESULTS

No increase in antibacterial activity against Escherichia coli was observed by adding either Fc or GA to p-Bt. However, Fc-p-Bt and GA-p-Bt exhibited improved activity against Staphylococcus aureus. No cytotoxicity upon fibroblast was observed for GA-p-Bt. On the other hand, conjugation with Fc increased cytotoxicity. This toxicity may be related to the membrane permeabilization capacity of this bioconjugate, which showed the highest carboxyfluorescein leakage in vesicle permeabilization experiments.

CONCLUSION

Considering these observations, our findings highlight the importance of adding bioactive organic compounds in the N-terminal position as a tool to modulate the activity of AMPs.

Tryptone-stabilized silver nanoparticles' potential to mitigate planktonic and biofilm growth forms of Serratia marcescens

Several microbial pathogens are capable of forming biofilms. These microbial communities pose a serious challenge to the healthcare sector as they are quite difficult to combat. Given the challenges associated with the antibiotic-based management of biofilms, the research focus has now been shifted towards finding alternate treatment strategies that can replace or complement the antibacterial properties of antibiotics. The field of nanotechnology offers several novel and revolutionary approaches to eradicate biofilm-forming microbes. In this study, we evaluated the antibacterial and antibiofilm efficacy of in-house synthesized, tryptone-stabilized silver nanoparticles (Ts-AgNPs) against the superbug Serratia marcescens. The nanoparticles were of spherical morphology with an average hydrodynamic diameter of 170 nm and considerable colloidal stability with a Zeta potential of - 24 ± 6.15 mV. Ts-AgNPs showed strong antibacterial activities with a minimum inhibitory concentration (MIC₅₀) of 2.5 µg/mL and minimum bactericidal concentration (MBC) of 12.5 µg/mL against S. marcescens. The nanoparticles altered the cell surface hydrophobicity and inhibited biofilm formation. The Ts-AgNPs were also effective in distorting pre-existing biofilms by degrading the extracellular DNA (eDNA) component of the extracellular polymeric substance (EPS) layer. Furthermore, reduction in quorum-sensing (QS)-induced virulence factors produced by S. marcescens indicated that Ts-AgNPs attenuated the QS pathway. Together, these findings suggest that Ts-AgNPs are an important anti-planktonic and antibiofilm agent that can be explored for both the prevention and treatment of infections caused by S. marcescens.

In Silico and In Vitro Analyses Reveal Promising Antimicrobial Peptides from Myxobacteria

Antimicrobial resistance (AMR) is a global concern, and as soon as new antibiotics are introduced, resistance to those agents emerges. Therefore, there is an increased appetite for alternative antimicrobial agents to traditional antibiotics. Here, we used in silico methods to investigate potential antimicrobial peptides (AMPs) from predatory myxobacteria. Six hundred seventy-two potential AMP sequences were extracted from eight complete myxobacterial genomes. Most putative AMPs were predicted to be active against Klebsiella pneumoniae with least activity being predicted against Staphylococcus aureus. One hundred seventeen AMPs (defined here as 'potent putative AMPs') were predicted to have very good activity against more than two bacterial pathogens, and these were characterized further in silico. All potent putative AMPs were predicted to have anti-inflammatory and antifungal properties, but none was predicted to be active against viruses. Twenty six (22%) of them were predicted to be hemolytic to human erythrocytes, five were predicted to have anticancer properties, and 56 (47%) were predicted to be biofilm active. In vitro assays using four synthesized AMPs showed high MIC values (e.g. So_ce_56_913 250 µg/ml and Coral_AMP411 125 µg/ml against E. coli). However, antibiofilm assays showed a substantial reduction in numbers (e.g. Coral_AMP411 and Myxo_mac104 showed a 69% and 73% reduction, respectively, at the lowest concentration against E. coli) compared to traditional antibiotics. Fourteen putative AMPs had high sequence similarity to proteins which were functionally associated with proteins of known function. The myxobacterial genomes also possessed a variety of biosynthetic gene clusters (BGCs) that can encode antimicrobial secondary metabolites, but their numbers did not correlate with those of the AMPs. We suggest that AMPs from myxobacteria are a promising source of novel antimicrobial agents with a plethora of biological properties.

Antimicrobial Peptides Therapy: An Emerging Alternative for Treating Drug-Resistant Bacteria

Microbial resistance to antibiotics is an ancient and dynamic issue that has brought a situation reminiscent of the pre-antibiotic era to the limelight. Currently, antibiotic resistance and the associated infections are widespread and pose significant global health and economic burden. Thus, the misuse of antibiotics, which has increased resistance, has necessitated the search for alternative therapeutic agents for combating resistant pathogens. Antimicrobial peptides (AMPs) hold promise as a viable therapeutic approach against drug-resistant pathogens. AMPs are oligopeptides with low molecular weight. They have broad-spectrum antimicrobial activities against pathogenic microorganisms. AMPs are nonspecific and target components of microbes that facilitate immune response by acting as the first-line defense mechanisms against invading pathogenic microbes. The diversity and potency of AMPs make them good candidates for alternative use. They could be used alone or in combination with several other biomaterials for improved therapeutic activity. They can also be employed in vaccine production targeting drug-resistant pathogens. This review covers the opportunities and advances in AMP discovery and development targeting antimicrobial resistance (AMR) bacteria. Briefly, it presents an overview of the global burden of the antimicrobial resistance crisis, portraying the global magnitude, challenges, and consequences. After that, it critically and comprehensively evaluates the potential roles of AMPs in addressing the AMR crisis, highlighting the major potentials and prospects.