Antimicrobial Peptides: Challenges and Future Perspectives

Antimicrobial Peptides: Challenges and Future Perspectives covers the latest developments about antimicrobial peptides in the scenario of drug resistance. The book is divided into 16 chapters arranged in sequence and preceded by chapters on historical developments and their role as regulatory molecules in innate defense mechanism. Emphasis is given to purification techniques and characterization suitable for interdisciplinary research. Chapters provide an inventory of various antimicrobial peptides, from a diverse array of organisms such as bacteria, fungi, insects, amphibians, plants and mammals. A section on marine ecosystem broadens readers understanding on marine based antimicrobial peptides.

Additional sections provide an informative overview on peptides with antiviral properties and those targeting multi-drug resistant bacteria. Recent reports and mechanism on resistance against antimicrobial peptides are also provided, along with key insights into the challenges and future perspectives of peptide drug development.

• Emphasizes antimicrobial peptides targeting various human viruses and multidrug resistant bacteria
• Written by internationally recognized experts who provide readers with a wide and useful perspective
• Provides in-depth resources for undertaking a research work in antimicrobial peptides with the inclusion of chapters on purification techniques and structural details
• Addresses the possibility and availability of peptide antibiotics in the global drug market
• Serves as a complete resource from the discovery to drug development of peptide antibiotics

• Language: English
• Publisher: Academic Press
• Release date: Nov 23, 2022
• ISBN: 9780323903202

Book preview

Preface

K. Ajesh and K. Sreejith

Among the great discoveries in the field of medicine, none is as prized as penicillin, which is considered the world’s first antibiotic. Mankind is indebted to the great Sir Alexander Fleming, who has saved millions of human beings from untimely deaths since then by this discovery. The discovery of penicillin was not merely accidental. It was the product of turning Sir Fleming’s intelligence into the consequences of an incident of negligence made during his experiments.

Although many great scientists and antibiotics—natural as well as synthetic forms—have been born in the world since penicillin, it remains a fact that microorganisms can survive them through various strategies and the predator–prey game that has been going on from the beginning of life continues to this day between antibiotics and microbes. Hence, in this era of exponentially increasing incidences of multiple drug-resistant infections globally, there is an urgent need to explore new areas in antimicrobial therapy, and peptide antibiotics are unquestionably seen as a potential solution.

It is at this point that peptides with antimicrobial properties are emerging as alternatives to conventional antibiotics. Antimicrobial peptides, as they are having broad-spectrum antimicrobial activity and have been shown to cause only low levels of drug resistance, making them highly promising clinical antibiotics of the future.

In this milieu, Antimicrobial Peptides: Challenges and Future Perspectives provides information pertinent to the antimicrobial peptides discovered through global research. The book presents several chapters starting from the historical developments to the global peptide antibiotic market. It also adds an array of techniques for peptide isolation and peptides from a wide range of organisms, including bacteria, fungi, insects, amphibians, mammals, and plants, and their analysis. Additional sections give a thorough overview of marine antimicrobial peptides, antiviral peptides, and those targeting multidrug-resistant bacteria. With the much recent information in computational biology and data sciences, the authors treat the chapters on antimicrobial peptide resistance and future perspectives of peptide drug development in an effective manner. This book will be a valuable resource for researchers, teachers, and students in microbiology, molecular biology, biochemistry, and other allied disciplines.

In this venture, we are deeply indebted to all the authors for doing an outstanding job in structuring their chapters more informative and understandable to the readers. We also want to thank our friends and colleagues from Kannur University, Kerala who have shared knowledge and concepts across the subject with us.

Finally, we would like to express appreciation to everyone at the Academic Press.

1

Historical developments of antimicrobial peptide research

Benu George¹, S. Pooja¹, T.V. Suchithra¹ and Denoj Sebastian²,    ¹School of Biotechnology, National Institute of Technology Calicut, Kattangal, Kerala, India,    ²Department of Life Sciences, University of Calicut, Thenhipalam, Kerala, India

Abstract

The dawn of the Golden age of antibiotics commenced in the year 1943, and scientists seemed to be incurious about the therapeutic potential of host immune defense mechanisms. Over the years, burgeoned emergence of antimicrobial-resistant microbes mushroomed the need for the discovery of novel antimicrobial agents. As compared to synthetic antibiotics, there are certain advantages to the implication of antimicrobial peptides (AMPs) such as delayed resistance, comprehensive antibiofilm activity, and the capacity to control the host immune response favorably. AMPs can be present in prokaryotes and eukaryotes, and it is believed that AMPs form the first line of the innate immune defense. Where the tissues and organs are exposed to pathogens, the occurrence of AMPs would be quite high. Thus in animals, AMPs play a major role in the defense mechanism before there are any symptoms. This review layouts the timeline for the development of AMPs and highlights its progress in pharmaceutical and various other fields. Further, it also takes into account the strategies attempted for the modification of AMPs during the timeframe of its development.

Keywords

Antimicrobial peptide; AMPs; cathelicidins; defensins; clinical developments; modification; history; timeline

1.1 Introduction

Several pathogenic strains have been well identified over the years. Humankind has also witnessed a friendly as well as a foe nature of pathogens as they are an integral part of the ecological niche. Various therapies based on synthetic sources have been proved beneficial to control these pathogenic invasions. But, would the story end there? As aware of the adapting capability of microbes over the years. The emergence of superbugs that are multidrug resistant has raised concerns about the use of synthetic antibiotics in the long run [1]. Thus improved variants of fluoroquinolones and imipenem have been serving as broad-spectrum drugs, but indeed, bacteria can become resistant to the variants by the alteration of known resistance mechanisms [2]. In the absence of an immune response, human beings and other species manage to stay uninfected because of the effectiveness of nonspecific defenses. The research identifies that organisms use cationic peptides as a nonspecific defense against infections [3]. Thus an urge for new antibiotics or antibacterial resources has directed scientists to explore peptide defense mechanism. Discovered in 1939, antimicrobial peptides (AMPs) or host defense peptides exhibit broad-spectrum and dynamic antimicrobial efficacy against bacteria, fungi, and viruses [4]. These peptides are crucial components of the innate immune system that endures against forging attacks and forms the first-line defense [5]. The antimicrobial mechanism that AMPs offer is unlike traditional antibiotics that make it possible for being functional against microbes that are even drug resistant [6].

The broad range activity for AMPs is attributed to their reduced toxicity and diminished target cell resistance development [7]. The AMPs occur in a varied range of α-helices, β-strands, loops, and extended structures. Such diversified secondary structures have been highly beneficial for AMPs’ broad-spectrum antimicrobial activity [8]. Researchers have observed that rapid diffusion and extracellular secretion of AMPs facilitate instant defense response against pathogenic microbes [9]. Alternatively, the differences in the lipid composition of cell membranes in prokaryotes and eukaryotes signify the targets for AMPs. Thus the specificity of AMPs incited against the target cell is extremely dependent on the interaction of peptides preferentially with the microbial cells, which enable AMPs to be target-specific without affecting the host cells [10]. The net charge and the hydrophobicity of AMPs form a vital component in the cellular association of peptides for target-specific antimicrobial activity [11]. However, to focus our discussion, this chapter reviews the developmental path of AMPs, their ancient origins, and evolution along with their functional development and emergence of the various database that has supported the development of AMPs.

1.2 History and development of antimicrobial peptides

It is fascinating to witness the evolution where every life form is always prayed by microbial infection. The adaptive immune system manages well to protect against infection. Nevertheless, the question is, how do plants and insects endure infections? They lack an adaptive immune system, yet it is all accomplished. Historically, the early report on the production of eukaryotic AMPs was a discovery from plants [12]. In 1896 the eukaryotic AMPs were primarily the research focus and by the mid-20thcentury cecropins from moths and magainins from frogs were discovered. Research on AMPs has flourished over the year 2000, mostly associated with all eukaryotic organisms. By the 1920s, Alexander Fleming identified lysozyme, which was considered the first peptide with antimicrobial activity [13]. However, lysozyme enzymatically destructs the bacterial cell wall; thus the discovery of lysozyme classifies a diverse category of AMPs, due to the mechanism of action [14]. Later in 1928, Fleming, Howard Florey, and Ernst Chain discovered penicillin [15], with the advent of therapeutic use of penicillin and streptomycin in 1943, the Golden Age of antibiotics, resulted in a relapse of curiosity in the therapeutic potential of natural host antibiotics [16].

Recognition of AMPs since 1939 emerged with gramicidins isolated from Bacillus brevis that were potent against a broad class of Gram-positive bacteria. As research flourished, gramicidins showed effectiveness to cure infected wounds on the skin of guinea pigs, demonstrating a clinical use [17], and thus first AMPs to be manufactured as antibiotics were established [18]. In the year 1942, the antimicrobial substance from the wheat endosperm (Triticum aestivum) was established as a peptide that inhibited the phytopathogens like Pseudomonas solanacearum and Xanthomonas campestris [19]. Far along, a peptide, purothionin (mid-1970s) [20], from the family of thionins was discovered [12]. However, with the dusk of age antibiotics due to the emergence of multidrug-resistant microbial pathogens, that is superbugs an awakening of host defense molecules was prompted [21]. At this point in history, the true origin of research into AMPs [22] emerged. And in the commencement of the 1950s and 1960s, it was learned that human neutrophils possess a cationic protein to kill bacteria via oxygen-independent mechanisms [23,24].

An increase in bacterial resistance to antibiotics led to the discovery of new therapeutic molecules that focus not only on drug prospection but also on its improved immune potential from the existing antibiotics. Chemical modifications of AMPs improve their stability, efficacy, as well as physical properties. Various analogous modification experiments resulted in designing peptides based on sequence and amphipathicity. In 1997 various natural peptides were investigated, and by observing the most predominant amino acids among 20 N-terminus residues of 80 different peptides, a model alpha-helical antibacterial peptide was synthesized [25].

Such chemically synthesized peptides are privileged and can undertake desired modification, specificity, stability, and toxicity. Thus the synthesized peptide in a hydrophobic environment adopts an alpha-helix, which many other alpha-helical peptides fail. Modification of AMPs offers a broad scope for developing cytotoxic peptide into a biocompatible peptide. Chemical modification of pardaxin achieved in 1999 enabled the peptide to retain its antimicrobial activity. Pardaxin displays lytic activity with both microbial and mammalian cells, but the addition of D-amino acid residues into the peptide alters the α-helix structure of pardaxin into β-structure [26]. Thus the β-structured pardaxin fails to display hemolytic activity as well as retains the antimicrobial activity.

It has been recognized that the chemical synthesis of peptides is a preferably beneficial method for preparing AMPs. In 2001 an investigation observed that a medium-sized peptide synthesis can be achieved by a standard way of solid-phase peptide synthesis method. Large and complex AMPs synthesis requires a combination of solid-phase peptide synthesis and in-solution fragment condensation or ligation techniques [27]. A report on 2016 signifies the importance of cyclization-based modifications in linear peptides and their effectiveness in improving membrane permeating ability of AMPs. Several linear peptides were cyclized and their stability, hydrophobicity, amphipathicity, and charge index were significantly enhanced, which resulted in increased membrane permeation of bacterial cells [28]. The reduced conformational flexibility of cyclic peptides enhances membrane disruption, thereby making AMPs an effective alternative to antibiotics. A site-elective modification of dehydroalanine and dehydrobutyrine by employing photoredox catalysis to natural peptide was achieved in 2018. Such site-selective change is meant to be a promising strategy since potential targets are often products of sophisticated biological posttranslational machinery, making it difficult to modify by means of common bio-orthogonal chemistry bioengineering approaches [29]. A study in 2020 evaluated the need for chemical modifications for a peptide, KR-12 minimalized antimicrobial fragment of human host peptide LL-37. The original activity of LL-37 was related to wound healing and biofilm activity. Further investigations on specific active fragments of peptides revealed that KR-12 exhibit similar antimicrobial potential as that of LL-37. Key positions of the fragment were Gln5 and Asp9, when substituted with Lys or Ala increased the broad-spectrum activity up to eightfold. Reversing the sequence of KR-12 and introducing cyclic dimers were found to increase the antifungal activity 4- to 16-fold. The addition of N-terminal cysteine and N-benzymidazolinone groups facilitate peptide cyclization and increases the ligation nature, which in turn improves the hydrophobicity and strengthens the disulfide bonds, resulting in increased cytotoxic activity [30].

Significantly chemical synthesized or modified AMPs are of great interest and a survey conducted in 2019 on small therapeutic peptides (less than 50 amino acids) approved by the Food and Drug Administration (FDA) in the previous two decades (Table 1.1) mostly consisted of receptor binding and inhibitor category [31]. Modifications can achieve precision in achieving the desired function for example, KYPROLIS approved in 2012 function as an inhibitor for multiple myeloma treatment. Development of such synthetic AMP or modified analogs helps in improving biological activities and metabolic stability of AMPs, which leads to arise smart antibiotics that aim to improve the therapies and industrial role of AMPs.

Table 1.1

1.3 Antimicrobial peptides as host innate defense barricade

As we know the evolutionary adaptability to withstand a foreign invasion from external sources is established by all life forms [32]. In higher organisms, AMPs develop as an element of innate immunity to protect against infection occurring in the host, which in contrast, for bacteria AMPs are triggered to survive in the same ecological niche [33]. AMPs extraordinarily exhibit a broad range of antimicrobial activity against organisms such as Gram-positive, Gram-negative bacteria, fungi, viruses, and unicellular protozoa [34,35]. Recently, several AMPs research has promising display results of pathogen clearance by modulating host innate immune response [36].

AMPs are a natural product of ribosomal translation of mRNA or nonribosomal peptide synthesis. Bacteria mainly form the nonribosomal peptides but the ribosomal AMPs synthesis is encoded genetically, which is found in all species, including bacteria [37]. The nonribosomal AMPs are well known as antibiotics (e.g., polymyxins and gramicidin S) and the ribosomal AMPs have been commonly known for their part in innate immunity [32,37,38].

The mammalian AMPs are typically found within the skin and mucosal epithelial cell secretions and neutrophil granules. [38–40]. The AMPs are mostly encoded in clusters and co-expressed, which results in the accumulation of numerous AMPs at a single site [41]. Fascinatingly, most AMPs are inactive precursor products that require a proteolytic cleavage to become active [42], so their expression depends on regulation as well as the surplus presence of suitable proteases [41]. In multicellular organisms, AMPs are stockpiled in greater concentrations as granules, which are inactive and released at the site of inflammation. Surprisingly, the AMPs in higher mammals are also an expression that is associated with pathogen-associated molecular patterns or cytokines responses [34,41].

1.4 Peptide-based database: barn house for AMPs

Several databases make it possible to learn about naturally occurring AMPs; these databases cover more than 23,253 peptides [43]. The sequences for AMPs are easily retrieved from UniProt database (http://www.uniprot.org) that contains peptide sequences in a large number with broad origins and functions. However, due to the comprehensive classification of peptides available, the AMPs databases are designed and modified to gather, and filter the information available for example, BACTIBASE for bacteriocins peptide sources and PhytAMP for plant-based peptide sources [44]. The database mostly classifies AMPs into two main groups: general and specific databases. The general databases are a depositary of all types of AMPs, irrespective of source and type. Specific databases are conserved to a specific number of peptides belonging to a particular source or family. The search option of the database utilizes sequence alignment tools to recognize likenesses between a given template and the deposited AMPs. However, the results are not promising due to low sequence similarity [45]. These databases also provide physicochemical profiles that help in evaluating the AMPs features.

Recently developed database, LAMP2 has an overall of unique 23,253 AMPs [43]. The unique designed AMPs database cross-link various databases and provide options to select individual databases as per the users’ need on the subject of interest. As the database updates, it would include details such as structure, collection, composition, source, and function activities of AMPs [43]. Similarly, the THPdb (http://crdd.osdd.net/raghava/thpdb/) represents a comprehensive database which is based on the Food Drug Administration approved or investigational therapeutic peptides [46]. The THPdb entries of AMPs are categorized into various classes based on function (Table 1.1). The entries in THPdb information are compiled from research papers, patents, the pharmaceutical company, drug bank, USFDA, and others. The database statically (Fig. 1.1B) shows that most of the entries of AMPs are intravenous, subcutaneous, and intramuscular administration. Only 5% of developed AMPs classes are orally administered. It can be observed that the AMPs entry in THPdb is mostly associated with receptor targets (47.6%) followed by protein and factors as targets (Fig. 1.1C). The entries of AMPs base on function (Fig. 1.1A) is classified as, Group Ia—replacing a protein that is deficient or abnormal; Group Ib—augmenting an existing pathway; Group Ic—providing a novel function or activity; Group IIa—interfering with a molecule or organism; Group IIb—delivering other compounds or proteins; Group IIIa—protecting against a deleterious foreign agent; Group IIIb—treating an autoimmune disease; Group IIIc—treating cancer; and Group IV—protein diagnostics.

Figure 1.1 Statistical distribution of AMPs in THPdb (A) based on function, (B) based on the route of administration, and (C) based on the target of AMPs. AMPs, Antimicrobial peptides.

1.5 Current timeline of antimicrobial peptide approvals

The peptide discovery in recent years has been trending among researchers. The research evolves from academic groups to create new peptide-focused companies and businesses to solve much of pharma drug alternatives [47,48]. Intestinally, of 208 new drugs approved by the USFDA, 15 drugs were peptides, or peptide-containing molecules (Fig. 1.2) and the rest belonged principle were 150 new chemical entities and 58 biologics in the last 5 years (2015–19) [49,50]. The unique place shared by peptide-approved drugs is with small molecules in completion. The peptide approvals by the FDA are an indication of pharmaceutical relevance as an active that display the diversity of the peptide realm.

Figure 1.2 Recent peptide-based drugs approved by the FDA (2015–19).

1.6 Chemical developments in AMPs

The stability of AMPs can be improved with the help of certain chemical modifications. Posttranslational modifications of natural peptides have significantly improved the bioactivity of peptides to a greater extent. Some of the common chemical modifications include terminal capping, D-amino acid modifications, halogenation, hydroxylation, oxidation, phosphorylation, glycosylation, sulfation, reduction, disulfide bridges, thioether bridges, and cyclization. AMPs can be conjugated (Table 1.2) with polymers such as polyethylene glycol, chitosan, hyaluronic acid, and hyperbranched glycerol (HPG) to develop drug conjugates with improved efficacy. A study conducted in 2017 showed the immunomodulatory effect of HPG-amine conjugates on red blood cells, which showed a tremendous therapeutic advantage over synthetic ones, owing to its lesser toxicity and antibiofilm activity [60]. Since then, HPG-based AMPs are screened for their activities. Despite having several advantages of conjugated/modified AMPs, there are certain demerits to it. Right from reduction of antimicrobial activity to loss of specificity of targets several issues have to be rectified to make the new-gen AMPs into the market. Considering the bioavailability and toxicity issues, certain posttranslational modifications for linear peptides have to be done before conjugating them with polymers [61].

Table 1.2

1.7 Antimicrobial peptides modification for medical application

The AMPs are potent against several multidrug-resistant bacteria and the mechanism of AMPs depends on their size, membrane permeability, and low anionic charge. There are four families of AMPs: cathelicidins, defensins, cercopins, and magainins. Peptides derived from eukaryotes are found to have more effective antimicrobial properties than those of commercial antibiotics [62]. Some of the AMPs from eukaryotes such as cathelicidins, bacitracin, telaprevir, and oritavancin are used for therapeutic applications.

Cathelicidins exhibit direct antimicrobial and excellent wound-healing activities by inducing chemotaxis and phagocytosis activities. Human cathelicidin (LL37), chicken cathelicidin (CATH), and porcine cathelicidin (protegrin, prophenin, and porcine myeloid antibacterial peptide) have a C-terminal domain rich in proline/arginine residues, which penetrates bacterial membranes and activates macrophages [63]. In addition to its antimicrobial and antibiofilm properties, they exhibit tissue repair and wound-healing properties. The origin of secretion and C-terminal domain of cathelicidins play a major role in determining its activity. For example, human cathelicidin (LL 37) has been linked with lung cancer due to its formyl-peptide receptors, which stimulates chemotaxis and suppresses tumorigenesis and plays a prominent role in metastasis of several types of cancer. On contrary, mouse cathelicidin-based AMPs are essential in downregulating azoxymethane-induced colon carcinogenesis [64]. Such drastic deviation in properties usually occurs in synthetic peptides than in natural ones. In some cases, immunotolerance of organism might chemically modify the amino acid terminal regions of peptides, resulting in downregulation of peptides. Halogenation is a common chemical modification occurring in cathelicidin from hagfish and centrocins, which exhibit lesser antimicrobial activity than their natural form [65].

Defensin peptides are another well-studied class of peptides, which is found excessively in plants, insects, and humans. The origin of human defensin occurs from neutrophils, as a part of innate immune response. First isolated human defensins (HD 5 and HD 6) were secreted from intestinal crypts and are found to exhibit antimicrobial and anti-tumor properties. There are two types of defensins existing in all organisms: α- and β-defensins, with different terminal amino acid residues contributing to their clinical applications. The change in alanine to aspartate in N-terminal domain of HDs results in reduced antimicrobial activity. Such single nucleotide changes reduce the net charge of peptide, limiting the antimicrobial activity. But, such modified natural defensins were found to be efficient in balancing the composition of intestinal microbiota. β-defensins, in addition to their bactericidal properties, were reported to be a protective agent against respiratory disorders, diarrhea, and sexual diseases. Human β-defensins (hBD), especially hBD-2,5, and 6, use lactoferrin and NaCl as co-factors to block viral replication. hBD-19,23 and 27 are modified forms of HD 6 that help in protecting male reproductive tract against colon infections. θ-defensin, identified in Macaca mulatta leukocytes exhibit stronger antiviral action against HIV and influenza virus. Similarly, rhesus θ-defensins exhibit bactericidal action against methicillin-resistant Staphylococcus aureus ((((MRSA) and Pseudomonas aeruginosa, which are resistant to several commercial antibiotics [66].

Many skin infections such as dermatitis, psoriasis, acne vulgaris, folliculitis, and rosacea can be treated/regulated with the help of AMPs. The wound healing and tissue repair ability of AMPs helps in maintaining the homeostasis of epithelial layer and increases the levels of cytokinins and interferons in the body, thereby stimulating innate immunity. Natural or synthetic modifications in AMPs resulted in more specific and targeted modes of action, thereby reduces the need for antibiotics. Some examples of therapeutic AMPs to treat skin infections are LL37, HD-6, Psoriasin, Pexiganan, Omiganan, Protegren-1, HBD-1,2, and P-novospirin G10 [66].

1.8 Antimicrobial peptides modification for industrial applications

Because of their antimicrobial nature, AMPs serve a direct linkage to crop protection. Cecropin and defensins isolated from several plant sources offer resistance to several crop infections. Alfalfa antifungal peptide isolated from the seeds of Alfalfa shows resistance toward Vetricillium dahliae, a harmful fungal pathogen of potatoes. Tachyplesin, an AMP isolated from crab, has been evaluated for its antifungal ability against Sclerotinia sclerotiorum. Inoculation of a specific AMP melittin to tobacco leaves helps in preventing the Tobacco mosaic virus entry into cells. The similarity of viral coat proteins with peptide sequence strengthens the immunity, thereby heightening the immune response. Expression of Attacin E in transgenic apple and pear resulted in bactericidal activity against fire blight disease. The introduction of magainin in grapevine resists the crown gall disease at a very early stage. AMPs also exhibit insecticidal activity and postharvest crop management. HP peptide derived from ribosomal protein of Helicobacter pylori has nematocidal activity against roundworm and insecticidal activity. To prevent postharvest crop decay, defensin genes in plants have to be activated, which gives long-term protection to crops. The use of AMPs such as tachyplesin 1, cecropin B, defensin A, and some antifungal peptides can be an environmental-friendly alternative to synthetic pesticides [67].

Despite having several advantages, peptides have certain undesirable characteristics which make it difficult to work on the targeted applications. Those reasons are low yield, toxicity index, and pharmacokinetic stability. Such issues can be dealt with the help of nanotechnology. Nanostructured peptides have lesser cytotoxicity, higher stability, and desired properties toward targeted applications. Some examples of nanostructured peptides are Cyclosporin A encapsulated with poly lactic acid-co-glycolide co-caprolactone, liposome-encapsulated nisin, vancomycin encapsulated with polycaprolactone or polylactic acid, and phospholipid encapsulated Polymyxin B. All these nanostructured peptides have higher cellular uptake, lesser toxicity, higher stability, and greater bioavailability than their free form [68].

Because of its greater antimicrobial potential, AMPs possess higher scope in food industry as well. Milk-derived AMPs were more promising food preservatives than other peptides. Lactoferrin and Lactoferricin B control spoilage of mozzarella cheese by limiting the growth of mesophilic bacteria. Lactoferrin-based spray has been utilized in carcass processing to prevent spoilage due to bacterial contamination. Several reports of using milk-based peptides in fruits and vegetables help in preventing food spoilage [69].

Several other AMPs have been discovered from marine microbiota, which controls pathogens in aquaculture as well as helps in maintaining immunity. Recent advancements of AMPs in aquaculture are in grafting process for the pearl industry. Tachyplesin when combined with exopolysaccharides can be used as a filming agent to reduce oyster postoperative mortality, thereby increasing pearl quantity. In case of seafood sectors, shrimps get contaminated with Vibrio penaeicida which makes it unsuitable for consumption, as it can cause several infections while consumed. This issue can be sorted by using Type II crustin, making it naturally immune to Vibrio infections. Other AMPs identified from Stylicins, Crustins, and Penaeidins have antimicrobial and anticancer applications. Interestingly, these marine classes of AMPs have reported wound healing and antiprotease activities. A special class of AMPs called arminins defines the host–pathogen interaction in marine microbiota and maintains the homeostasis of beneficial microbiota