Special Issue "Antimicrobial Peptides"

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A special issue of Antibiotics (ISSN 2079-6382).

Deadline for manuscript submissions: closed (31 August 2014)

Special Issue Editor

Guest Editor
Dr. William M. Shafer

Department of Microbiology and Immunology, School of Medicine, Emory University, Rollins Research Center, Atlanta, GA, USA
Website | E-Mail
Phone: 1+404-805-1822
Interests: antimicrobial peptides; evolution; molecular biology; regulation; synthesis; structure-function; host defense; bacterial diseases; immune-modulation; inflammation

Special Issue Information

Dear Colleagues,

This issue of Antibiotics is dedicated to the topic of antimicrobial peptides (AMPs), which are now recognized as important mediators of innate defense against microbial infections. Primary research manuscripts and review articles dealing with AMPs that emphasize their structure-function, biosynthesis and regulation, evolution, contribution to host defense, immune-modulatory activities, contributions to the pathophysiology of diseases, development of AMPs as therapeutic agents or mechanisms of action, as well as systems used by microbes to resist their antimicrobial action and how such resistance contributes to microbial pathogenesis, are invited.Submitted manuscripts will be peer-reviewed to ensure that the issue contains high quality contributions. Collectively, this issue will provide the readership with the most up-to-date information on AMPs.

Dr. William M. Shafer
Guest Editor

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Antibiotics is an international peer-reviewed Open Access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 300 CHF (Swiss Francs). English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

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Keywords

  • antimicrobial peptides
  • evolution, molecular biology
  • regulation
  • synthesis
  • structure-function
  • host defense
  • bacterial diseases
  • immune-modulation
  • inflammation

Published Papers (15 papers)

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Research

Jump to: Review

Open AccessArticle Structure-Dependent Immune Modulatory Activity of Protegrin-1 Analogs
Antibiotics 2014, 3(4), 694-713; doi:10.3390/antibiotics3040694
Received: 12 September 2014 / Revised: 31 October 2014 / Accepted: 13 November 2014 / Published: 27 November 2014
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Abstract
Protegrins are porcine antimicrobial peptides (AMPs) that belong to the cathelicidin family of host defense peptides. Protegrin-1 (PG-1), the most investigated member of the protegrin family, is an arginine-rich peptide consisting of 18 amino acid residues, its main chain adopting a β-hairpin structure
[...] Read more.
Protegrins are porcine antimicrobial peptides (AMPs) that belong to the cathelicidin family of host defense peptides. Protegrin-1 (PG-1), the most investigated member of the protegrin family, is an arginine-rich peptide consisting of 18 amino acid residues, its main chain adopting a β-hairpin structure that is linked by two disulfide bridges. We report on the immune modulatory activity of PG-1 and its analogs in neutralizing bacterial endotoxin and capsular polysaccharides, consequently inhibiting inflammatory mediators’ release from macrophages. We demonstrate that the β-hairpin structure motif stabilized with at least one disulfide bridge is a prerequisite for the immune modulatory activity of this type of AMP. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
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Open AccessArticle Killing of Staphylococci by θ-Defensins Involves Membrane Impairment and Activation of Autolytic Enzymes
Antibiotics 2014, 3(4), 617-631; doi:10.3390/antibiotics3040617
Received: 23 September 2014 / Revised: 30 October 2014 / Accepted: 31 October 2014 / Published: 14 November 2014
Cited by 10 | PDF Full-text (4326 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
θ-Defensins are cyclic antimicrobial peptides expressed in leukocytes of Old world monkeys. To get insight into their antibacterial mode of action, we studied the activity of RTDs (rhesus macaque θ-defensins) against staphylococci. We found that in contrast to other defensins, RTDs do not
[...] Read more.
θ-Defensins are cyclic antimicrobial peptides expressed in leukocytes of Old world monkeys. To get insight into their antibacterial mode of action, we studied the activity of RTDs (rhesus macaque θ-defensins) against staphylococci. We found that in contrast to other defensins, RTDs do not interfere with peptidoglycan biosynthesis, but rather induce bacterial lysis in staphylococci by interaction with the bacterial membrane and/or release of cell wall lytic enzymes. Potassium efflux experiments and membrane potential measurements revealed that the membrane impairment by RTDs strongly depends on the energization of the membrane. In addition, RTD treatment caused the release of Atl-derived cell wall lytic enzymes probably by interaction with membrane-bound lipoteichoic acid. Thus, the premature and uncontrolled activity of these enzymes contributes strongly to the overall killing by θ-defensins. Interestingly, a similar mode of action has been described for Pep5, an antimicrobial peptide of bacterial origin. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Figures

Open AccessArticle Position-Dependent Influence of the Three Trp Residues on the Membrane Activity of the Antimicrobial Peptide, Tritrpticin
Antibiotics 2014, 3(4), 595-616; doi:10.3390/antibiotics3040595
Received: 15 September 2014 / Revised: 23 October 2014 / Accepted: 23 October 2014 / Published: 6 November 2014
Cited by 1 | PDF Full-text (4442 KB) | HTML Full-text | XML Full-text
Abstract
Antimicrobial peptides (AMPs) constitute promising candidates for the development of new antibiotics. Among the ever-expanding family of AMPs, tritrpticin has strong antimicrobial activity against a broad range of pathogens. This 13-residue peptide has an unusual amino acid sequence that is almost symmetrical and
[...] Read more.
Antimicrobial peptides (AMPs) constitute promising candidates for the development of new antibiotics. Among the ever-expanding family of AMPs, tritrpticin has strong antimicrobial activity against a broad range of pathogens. This 13-residue peptide has an unusual amino acid sequence that is almost symmetrical and features three central Trp residues with two Arg residues near each end of the peptide. In this work, the role of the three sequential Trp residues in tritrpticin was studied in a systematic fashion by making a series of synthetic peptides with single-, double- and triple-Trp substitutions to Tyr or Ala. 1H NMR and fluorescence spectroscopy demonstrated the ability of all of the tritrpticin-analog peptides to interact with negatively-charged membranes. Consequently, most tritrpticin analogs exhibited the ability to permeabilize synthetic ePC:ePG (egg-yolk phosphatidylcholine (ePC), egg-yolk phosphatidylglycerol (ePG)) vesicles and live Escherichia coli bacteria. The membrane perturbation characteristics were highly dependent on the location of the Trp residue substitution, with Trp6 being the most important residue and Trp8 the least. The membrane permeabilization activity of the peptides in synthetic and biological membranes was directly correlated with the antimicrobial potency of the peptides against E. coli. These results contribute to the understanding of the role of each of the three Trp residues to the antimicrobial activity of tritrpticin. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Figures

Open AccessArticle Antimicrobial Activity of Chemokine CXCL10 for Dermal and Oral Microorganisms
Antibiotics 2014, 3(4), 527-539; doi:10.3390/antibiotics3040527
Received: 4 September 2014 / Revised: 3 October 2014 / Accepted: 14 October 2014 / Published: 23 October 2014
Cited by 2 | PDF Full-text (587 KB) | HTML Full-text | XML Full-text
Abstract
CXCL10 (IP-10) is a small 10 kDa chemokine with antimicrobial activity. It is induced by IFN-γ, chemoattracts mononuclear cells, and promotes adhesion of T cells. Recently, we detected CXCL10 on the surface of the skin and in the oral cavity. In the current
[...] Read more.
CXCL10 (IP-10) is a small 10 kDa chemokine with antimicrobial activity. It is induced by IFN-γ, chemoattracts mononuclear cells, and promotes adhesion of T cells. Recently, we detected CXCL10 on the surface of the skin and in the oral cavity. In the current study, we used broth microdilution and radial diffusion assays to show that CXCL10 inhibits the growth of Escherichia coli, Staphylococcus aureus, Corynebacterium jeikeium, Corynebacterium striatum, and Candida albicans HMV4C, but not Corynebacterium bovis, Streptococcus mutans, Streptococcus mitis, Streptococcus sanguinis, Fusobacterium nucleatum, Aggregatibacter actinomycetemcomitans, Poryphromonas gingivalis, or C. albicans ATCC 64124. The reason for the selective antimicrobial activity is not yet known. However, antimicrobial activity of CXCL10 may be related to its composition and structure, as a cationic 98 amino acid residue molecule with 10 lysine residues, 7 arginine residues, a total net charge of +11, and a theoretical pI of 9.93. Modeling studies revealed that CXCL10 contains an α-helix at the N-terminal, three anti-parallel β-strands in the middle, and an α-helix at the C-terminal. Thus, CXCL10, when produced on the surface of the skin or in the oral cavity, likely has antimicrobial activity and may enhance innate antimicrobial and cellular responses to the presence of select commensal or opportunistic microorganisms. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessArticle Anti-Biofilm and Immunomodulatory Activities of Peptides That Inhibit Biofilms Formed by Pathogens Isolated from Cystic Fibrosis Patients
Antibiotics 2014, 3(4), 509-526; doi:10.3390/antibiotics3040509
Received: 18 August 2014 / Revised: 8 October 2014 / Accepted: 14 October 2014 / Published: 20 October 2014
Cited by 5 | PDF Full-text (1149 KB) | HTML Full-text | XML Full-text
Abstract
Cystic fibrosis (CF) patients often acquire chronic respiratory tract infections due to Pseudomonas aeruginosa and Burkholderia cepacia complex (Bcc) species. In the CF lung, these bacteria grow as multicellular aggregates termed biofilms. Biofilms demonstrate increased (adaptive) resistance to conventional antibiotics, and there are
[...] Read more.
Cystic fibrosis (CF) patients often acquire chronic respiratory tract infections due to Pseudomonas aeruginosa and Burkholderia cepacia complex (Bcc) species. In the CF lung, these bacteria grow as multicellular aggregates termed biofilms. Biofilms demonstrate increased (adaptive) resistance to conventional antibiotics, and there are currently no available biofilm-specific therapies. Using plastic adherent, hydroxyapatite and flow cell biofilm models coupled with confocal and scanning electron microscopy, it was demonstrated that an anti-biofilm peptide 1018 prevented biofilm formation, eradicated mature biofilms and killed biofilms formed by a wide range of P. aeruginosa and B. cenocepacia clinical isolates. New peptide derivatives were designed that, compared to their parent peptide 1018, showed similar or decreased anti-biofilm activity against P. aeruginosa biofilms, but increased activity against biofilms formed by the Gram-positive bacterium methicillin resistant Staphylococcus aureus. In addition, some of these new peptide derivatives retained the immunomodulatory activity of 1018 since they induced the production of the chemokine monocyte chemotactic protein-1 (MCP-1) and suppressed lipopolysaccharide-mediated tumor necrosis factor-α (TNF-α) production by human peripheral blood mononuclear cells (PBMC) and were non-toxic towards these cells. Peptide 1018 and its derivatives provide promising leads for the treatment of chronic biofilm infections and hyperinflammatory lung disease in CF patients. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessArticle Differential Susceptibility of Bacteria to Mouse Paneth Cell a-Defensins under Anaerobic Conditions
Antibiotics 2014, 3(4), 493-508; doi:10.3390/antibiotics3040493
Received: 9 September 2014 / Revised: 28 September 2014 / Accepted: 8 October 2014 / Published: 17 October 2014
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Abstract
Small intestinal Paneth cells secrete a-defensin peptides, termed cryptdins (Crps) in mice, into the intestinal lumen, where they confer immunity to oral infections and define the composition of the ileal microbiota. In these studies, facultative bacteria maintained under aerobic or anaerobic conditions displayed
[...] Read more.
Small intestinal Paneth cells secrete a-defensin peptides, termed cryptdins (Crps) in mice, into the intestinal lumen, where they confer immunity to oral infections and define the composition of the ileal microbiota. In these studies, facultative bacteria maintained under aerobic or anaerobic conditions displayed differential sensitivities to mouse a-defensins under in vitro assay conditions. Regardless of oxygenation, Crps 2 and 3 had robust and similar bactericidal activities against S. typhimurium and S. flexneri, but Crp4 activity against S. flexneri was attenuated in the absence of oxygen. Anaerobic bacteria varied in their susceptibility to Crps 2-4, with Crp4 showing less activity than Crps 2 and 3 against Enterococcus faecalis, and Bacteroides fragilis in anaerobic assays, but Fusobacterium necrophorum was killed only by Crp4 and not by Crps 2 and 3. The influence of anaerobiosis in modulating Crp bactericidal activities in vitro suggests that a-defensin effects on the enteric microbiota may be subject to regulation by local oxygen tension. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessArticle Ciprofloxacin Affects Host Cells by Suppressing Expression of the Endogenous Antimicrobial Peptides Cathelicidins and Beta-Defensin-3 in Colon Epithelia
Antibiotics 2014, 3(3), 353-374; doi:10.3390/antibiotics3030353
Received: 27 May 2014 / Revised: 14 July 2014 / Accepted: 15 July 2014 / Published: 25 July 2014
Cited by 1 | PDF Full-text (1727 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Antibiotics exert several effects on host cells including regulation of immune components. Antimicrobial peptides (AMPs), e.g., cathelicidins and defensins display multiple functions in innate immunity. In colonic mucosa, cathelicidins are induced by butyrate, a bacterial fermentation product. Here, we investigated the effect of
[...] Read more.
Antibiotics exert several effects on host cells including regulation of immune components. Antimicrobial peptides (AMPs), e.g., cathelicidins and defensins display multiple functions in innate immunity. In colonic mucosa, cathelicidins are induced by butyrate, a bacterial fermentation product. Here, we investigated the effect of antibiotics on butyrate-induced expression of cathelicidins and beta-defensins in colon epithelial cells. Real-time PCR analysis revealed that ciprofloxacin and clindamycin reduce butyrate-induced transcription of the human cathelicidin LL-37 in the colonic epithelial cell line HT-29. Suppression of LL-37 peptide/protein by ciprofloxacin was confirmed by Western blot analysis. Immunohistochemical analysis demonstrated that ciprofloxacin suppresses the rabbit cathelicidin CAP-18 in rectal epithelia of healthy and butyrate-treated Shigella-infected rabbits. Ciprofloxacin also down-regulated butyrate-induced transcription of the human beta-defensin-3 in HT-29 cells. Microarray analysis of HT-29 cells revealed upregulation by butyrate with subsequent down-regulation by ciprofloxacin of additional genes encoding immune factors. Dephosphorylation of histone H3, an epigenetic event provided a possible mechanism of the suppressive effect of ciprofloxacin. Furthermore, LL-37 peptide inhibited Clostridium difficile growth in vitro. In conclusion, ciprofloxacin and clindamycin exert immunomodulatory function by down-regulating AMPs and other immune components in colonic epithelial cells. Suppression of AMPs may contribute to the overgrowth of C. difficile, causing antibiotic-associated diarrhea. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available

Review

Jump to: Research

Open AccessReview Host Defense Peptides from Asian Frogs as Potential Clinical Therapies
Antibiotics 2015, 4(2), 136-159; doi:10.3390/antibiotics4020136
Received: 10 November 2014 / Revised: 28 February 2015 / Accepted: 4 March 2015 / Published: 30 March 2015
Cited by 1 | PDF Full-text (1806 KB) | HTML Full-text | XML Full-text
Abstract
Host defense peptides (HDPs) are currently major focal points of medical research as infectious microbes are gaining resistance to existing drugs. They are effective against multi-drug resistant pathogens due to their unique primary target, biological membranes, and their peculiar mode of action. Even
[...] Read more.
Host defense peptides (HDPs) are currently major focal points of medical research as infectious microbes are gaining resistance to existing drugs. They are effective against multi-drug resistant pathogens due to their unique primary target, biological membranes, and their peculiar mode of action. Even though HDPs from 60 Asian frog species belonging to 15 genera have been characterized, research into these peptides is at a very early stage. The purpose of this review is to showcase the status of peptide research in Asia. Here we provide a summary of HDPs from Asian frogs. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessReview NETs and CF Lung Disease: Current Status and Future Prospects
Antibiotics 2015, 4(1), 62-75; doi:10.3390/antibiotics4010062
Received: 30 October 2014 / Accepted: 5 January 2015 / Published: 15 January 2015
Cited by 3 | PDF Full-text (831 KB) | HTML Full-text | XML Full-text
Abstract
Cystic Fibrosis (CF) is the most common fatal monogenic disease among Caucasians. While CF affects multiple organ systems, the principle morbidity arises from progressive destruction of lung architecture due to chronic bacterial infection and inflammation. It is characterized by an innate immune defect
[...] Read more.
Cystic Fibrosis (CF) is the most common fatal monogenic disease among Caucasians. While CF affects multiple organ systems, the principle morbidity arises from progressive destruction of lung architecture due to chronic bacterial infection and inflammation. It is characterized by an innate immune defect that results in colonization of the airways with bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa from an early age. Within the airway microenvironment the innate immune cells including epithelial cells, neutrophils, and macrophages have all been implicated in the host defense defect. The neutrophil, however, is the principal effector cell facilitating bacterial killing, but also participates in lung damage. This is evidenced by a disproportionately elevated neutrophil burden in the airways and increased neutrophil products capable of tissue degradation, such as neutrophil elastase. The CF airways also contain an abundance of nuclear material that may be originating from neutrophils. Neutrophil extracellular traps (NETs) are the product of a novel neutrophil death process that involves the expulsion of nuclear material embedded with histones, proteases, and antimicrobial proteins and peptides. NETs have been postulated to contribute to the bacterial killing capacity of neutrophils, however they also function as a source of proteases and other neutrophil products that may contribute to lung injury. Targeting nuclear material with inhaled DNase therapy improves lung function and reduces exacerbations in CF and some of these effects may be due to the degradation of NETs. We critically discuss the evidence for an antimicrobial function of NETs and their potential to cause lung damage and inflammation. We propose that CF animal models that recapitulate the human CF phenotype such as the CFTR−/− pig may be useful in further elucidating a role for NETs. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessReview Augmentation of Cationic Antimicrobial Peptide Production with Histone Deacetylase Inhibitors as a Novel Epigenetic Therapy for Bacterial Infections
Antibiotics 2015, 4(1), 44-61; doi:10.3390/antibiotics4010044
Received: 4 October 2014 / Accepted: 23 December 2014 / Published: 12 January 2015
Cited by 2 | PDF Full-text (677 KB) | HTML Full-text | XML Full-text
Abstract
The emergence of antibiotic resistance seriously threatens our ability to treat many common and medically important bacterial infections. Novel therapeutics are needed that can be used alone or in conjunction with antibiotics. Cationic antimicrobial peptides (CAMPs) are important effectors of the host innate
[...] Read more.
The emergence of antibiotic resistance seriously threatens our ability to treat many common and medically important bacterial infections. Novel therapeutics are needed that can be used alone or in conjunction with antibiotics. Cationic antimicrobial peptides (CAMPs) are important effectors of the host innate defense that exhibit broad-spectrum activity against a wide range of microorganisms. CAMPs are carried within phagocytic granules and are constitutively or inducibly expressed by multiple cell types, including epithelial cells. The role of histone modification enzymes, specifically the histone deacetylases (HDAC), in down-regulating the transcription of CAMP-encoding genes is increasingly appreciated as is the capacity of HDAC inhibitors (HDACi) to block the action of HDACs to increase CAMP expression. The use of synthetic and natural HDACi molecules to increase CAMPs on mucosal surfaces, therefore, has potential therapeutic applications. Here, we review host and pathogen regulation of CAMP expression through the induction of HDACs and assess the therapeutic potential of natural and synthetic HDACi based on evidence from tissue culture systems, animal models, and clinical trials. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessReview Mechanisms of Antimicrobial Peptide Resistance in Gram-Negative Bacteria
Antibiotics 2015, 4(1), 18-41; doi:10.3390/antibiotics4010018
Received: 26 September 2014 / Accepted: 21 November 2014 / Published: 25 December 2014
Cited by 12 | PDF Full-text (1887 KB) | HTML Full-text | XML Full-text
Abstract
Cationic antimicrobial peptides (CAMPs) are important innate immune defenses that inhibit colonization by pathogens and contribute to clearance of infections. Gram-negative bacterial pathogens are a major target, yet many of them have evolved mechanisms to resist these antimicrobials. These resistance mechanisms can be
[...] Read more.
Cationic antimicrobial peptides (CAMPs) are important innate immune defenses that inhibit colonization by pathogens and contribute to clearance of infections. Gram-negative bacterial pathogens are a major target, yet many of them have evolved mechanisms to resist these antimicrobials. These resistance mechanisms can be critical contributors to bacterial virulence and are often crucial for survival within the host. Here, we summarize methods used by Gram-negative bacteria to resist CAMPs. Understanding these mechanisms may lead to new therapeutic strategies against pathogens with extensive CAMP resistance. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessReview The Role of Cationic Polypeptides in Modulating HIV-1 Infection of the Cervicovaginal Mucosa
Antibiotics 2014, 3(4), 677-693; doi:10.3390/antibiotics3040677
Received: 3 September 2014 / Revised: 17 September 2014 / Accepted: 13 November 2014 / Published: 26 November 2014
Cited by 1 | PDF Full-text (591 KB) | HTML Full-text | XML Full-text
Abstract
The mucosa and overlying fluid of the female reproductive tract (FRT) are portals for the heterosexual transmission of HIV-1. Toward the ongoing development of topically applied microbicides and mucosal vaccines against HIV-1, it is evermore important to understand how the dynamic FRT mucosa
[...] Read more.
The mucosa and overlying fluid of the female reproductive tract (FRT) are portals for the heterosexual transmission of HIV-1. Toward the ongoing development of topically applied microbicides and mucosal vaccines against HIV-1, it is evermore important to understand how the dynamic FRT mucosa is involved in controlling transmission and infection of HIV-1. Cationic peptides and proteins are the principal innate immune effector molecules of mucosal surfaces, and interact in a combinatorial fashion to modulate HIV-1 infection of the cervix and vagina. While cationic peptides and proteins have historically been categorized as antimicrobial or have other host-benefitting roles, an increasing number of these molecules have been found to augment HIV-1 infection and potentially antagonize host defense. Complex environmental factors such as hormonal fluctuations and/or bacterial and viral co-infections provide additional challenges to both experimentation and interpretation of results. In the context of heterosexual transmission of HIV-1, this review explores how various cationic peptides and proteins participate in modulating host defense against HIV-1 of the cervicovaginal mucosa. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessReview Host Antimicrobial Peptides in Bacterial Homeostasis and Pathogenesis of Disease
Antibiotics 2014, 3(4), 645-676; doi:10.3390/antibiotics3040645
Received: 29 September 2014 / Revised: 5 November 2014 / Accepted: 5 November 2014 / Published: 17 November 2014
Cited by 2 | PDF Full-text (1294 KB) | HTML Full-text | XML Full-text
Abstract
Innate immune responses function as a first line of host defense against the development of bacterial infection, and in some cases to preserve the sterility of privileged sites in the human host. Bacteria that enter these sites must counter host responses for colonization.
[...] Read more.
Innate immune responses function as a first line of host defense against the development of bacterial infection, and in some cases to preserve the sterility of privileged sites in the human host. Bacteria that enter these sites must counter host responses for colonization. From the host’s perspective, the innate immune system works expeditiously to minimize the bacterial threat before colonization and subsequent dysbiosis. The multifactorial nature of disease further challenges predictions of how each independent variable influences bacterial pathogenesis. From bacterial colonization to infection and through disease, the microenvironments of the host are in constant flux as bacterial and host factors contribute to changes at the host-pathogen interface, with the host attempting to eradicate bacteria and the bacteria fighting to maintain residency. A key component of this innate host response towards bacterial infection is the production of antimicrobial peptides (AMPs). As an early component of the host response, AMPs modulate bacterial load and prevent establishment of infection. Under quiescent conditions, some AMPs are constitutively expressed by the epithelium. Bacterial infection can subsequently induce production of other AMPs in an effort to maintain sterility, or to restrict colonization. As demonstrated in various studies, the absence of a single AMP can influence pathogenesis, highlighting the importance of AMP concentration in maintaining homeostasis. Yet, AMPs can increase bacterial virulence through the co-opting of the peptides or alteration of bacterial virulence gene expression. Further, bacterial factors used to subvert AMPs can modify host microenvironments and alter colonization of the residential flora that principally maintain homeostasis. Thus, the dynamic interplay between host defense peptides and bacterial factors produced to quell peptide activity play a critical role in the progression and outcome of disease. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
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Open AccessReview Resistance to Antimicrobial Peptides in Vibrios
Antibiotics 2014, 3(4), 540-563; doi:10.3390/antibiotics3040540
Received: 16 September 2014 / Revised: 25 September 2014 / Accepted: 8 October 2014 / Published: 27 October 2014
Cited by 3 | PDF Full-text (832 KB) | HTML Full-text | XML Full-text
Abstract
Vibrios are associated with a broad diversity of hosts that produce antimicrobial peptides (AMPs) as part of their defense against microbial infections. In particular, vibrios colonize epithelia, which function as protective barriers and express AMPs as a first line of chemical defense against
[...] Read more.
Vibrios are associated with a broad diversity of hosts that produce antimicrobial peptides (AMPs) as part of their defense against microbial infections. In particular, vibrios colonize epithelia, which function as protective barriers and express AMPs as a first line of chemical defense against pathogens. Recent studies have shown they can also colonize phagocytes, key components of the animal immune system. Phagocytes infiltrate infected tissues and use AMPs to kill the phagocytosed microorganisms intracellularly, or deliver their antimicrobial content extracellularly to circumvent tissue infection. We review here the mechanisms by which vibrios have evolved the capacity to evade or resist the potent antimicrobial defenses of the immune cells or tissues they colonize. Among their strategies to resist killing by AMPs, primarily vibrios use membrane remodeling mechanisms. In particular, some highly resistant strains substitute hexaacylated Lipid A with a diglycine residue to reduce their negative surface charge, thereby lowering their electrostatic interactions with cationic AMPs. As a response to envelope stress, which can be induced by membrane-active agents including AMPs, vibrios also release outer membrane vesicles to create a protective membranous shield that traps extracellular AMPs and prevents interaction of the peptides with their own membranes. Finally, once AMPs have breached the bacterial membrane barriers, vibrios use RND efflux pumps, similar to those of other species, to transport AMPs out of their cytoplasmic space. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available
Open AccessReview Antimicrobial Peptide Resistance Mechanisms of Gram-Positive Bacteria
Antibiotics 2014, 3(4), 461-492; doi:10.3390/antibiotics3040461
Received: 28 August 2014 / Revised: 25 September 2014 / Accepted: 28 September 2014 / Published: 13 October 2014
Cited by 12 | PDF Full-text (996 KB) | HTML Full-text | XML Full-text
Abstract
Antimicrobial peptides, or AMPs, play a significant role in many environments as a tool to remove competing organisms. In response, many bacteria have evolved mechanisms to resist these peptides and prevent AMP-mediated killing. The development of AMP resistance mechanisms is driven by direct
[...] Read more.
Antimicrobial peptides, or AMPs, play a significant role in many environments as a tool to remove competing organisms. In response, many bacteria have evolved mechanisms to resist these peptides and prevent AMP-mediated killing. The development of AMP resistance mechanisms is driven by direct competition between bacterial species, as well as host and pathogen interactions. Akin to the number of different AMPs found in nature, resistance mechanisms that have evolved are just as varied and may confer broad-range resistance or specific resistance to AMPs. Specific mechanisms of AMP resistance prevent AMP-mediated killing against a single type of AMP, while broad resistance mechanisms often lead to a global change in the bacterial cell surface and protect the bacterium from a large group of AMPs that have similar characteristics. AMP resistance mechanisms can be found in many species of bacteria and can provide a competitive edge against other bacterial species or a host immune response. Gram-positive bacteria are one of the largest AMP producing groups, but characterization of Gram-positive AMP resistance mechanisms lags behind that of Gram-negative species. In this review we present a summary of the AMP resistance mechanisms that have been identified and characterized in Gram-positive bacteria. Understanding the mechanisms of AMP resistance in Gram-positive species can provide guidelines in developing and applying AMPs as therapeutics, and offer insight into the role of resistance in bacterial pathogenesis. Full article
(This article belongs to the Special Issue Antimicrobial Peptides) Print Edition available

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