Evaluation of susceptibility of gram-positive and -negative bacteria to human defensins by using radial diffusion assay

In vitro activity of human defensins HNP-1 and hBD-3 against multidrug-resistant ESKAPE Gram-negatives of clinical origin and selected peptidoglycan recycling-defective mutants

The use of immune compounds as antimicrobial adjuvants is a classic idea recovering timeliness in the current antibiotic resistance scenario. However, the activity of certain antimicrobial peptides against ESKAPE Gram-negatives has not been sufficiently investigated. The objective of this study was to determine the activities of human defensins HNP-1 and hBD-3 alone or combined with permeabilizing/peptidoglycan-targeting agents against clinical ESKAPE Gram-negatives [Acinetobacter baumannii (AB), Enterobacter cloacae (EC), Klebsiella pneumoniae (KP), and acute/chronic Pseudomonas aeruginosa (PA)]. Lethal concentrations (LCs) of HNP-1 and hBD-3 were determined in four collections of multidrug resistant EC, AB, KP, and PA clinical strains (10-36 isolates depending on the collection). These defensins act through membrane permeabilization plus peptidoglycan building blockade, enabling that alterations in peptidoglycan recycling may increase their activity, which is why different recycling-defective mutants were also included. Combinations with physiological lysozyme and subinhibitory colistin for bactericidal activities determination, and with meropenem for minimum inhibitory concentrations (MICs), were also assessed. HNP-1 showed undetectable activity (LC > 32 mg/L for all strains). hBD-3 showed appreciable activities: LC ranges 2-16, 8-8, 8->32, and 8->32 mg/L for AB, EC, KP, and PA, being PA strains from cystic fibrosis significantly more resistant than acute origin ones. None of the peptidoglycan recycling-defective mutants showed greater susceptibility to HNP-1/hBD-3. Combination with colistin or lysozyme did not change their bactericidal power, and virtually neither did meropenem + hBD-3 compared to meropenem MICs. This is the first study comparatively analyzing the HNP-1/hBD-3 activities against the ESKAPE Gram-negatives, and demonstrates interesting bactericidal capacities of hBD-3 mostly against AB and EC.

IMPORTANCE

In the current scenario of critical need for new antimicrobials against multidrug-resistant bacteria, all options must be considered, including classic ideas such as the use of purified immune compounds. However, information regarding the activity of certain human defensins against ESKAPE Gram-negatives was incomplete. This is the first study comparatively assessing the in vitro activity of two membrane-permeabilizing/peptidoglycan construction-blocking defensins (HNP-1 and hBD-3) against relevant clinical collections of ESKAPE Gram-negatives, alone or in combination with permeabilizers, additional peptidoglycan-targeting attacks, or the blockade of its recycling. Our data suggest that hBD-3 has a notable bactericidal activity against multidrug-resistant Acinetobacter baumannii and Enterobacter cloacae strains that should be considered as potential adjuvant option. Our results suggest for the first time an increased resistance of Pseudomonas aeruginosa strains from chronic infection compared to acute origin ones, and provide new clues about the predominant mode of action of hBD-3 against Gram-negatives (permeabilization rather than peptidoglycan-targeting).

The Antimicrobial Peptide Melectin Shows Both Antimicrobial and Antitumor Activity via Membrane Interference and DNA Binding

Purpose

Increasingly complex diseases require novel drugs for their treatment. Antimicrobial peptides (AMPs) are promising candidate treatments due to their broad existence and special characteristics. However, the current understanding of AMPs is not sufficient to allow them to be produced commercially for clinical use.

Materials and Methods

Melectin, from the venom of the cleptoparasitic bee Melecta albifrons, does not exhibit sequence homology with other wasp venom peptides. To investigate this more deeply, we explored the antibacterial and antitumor activities of Melectin and related mechanisms.

Results

Our results demonstrate that Melectin possesses antimicrobial properties against standard sensitive/clinical drug-resistant bacteria strains as well as antitumor activity. It has an α-helix form and exhibits moderate cytotoxicity. Its action mechanisms are involved with membrane interfering and DNA binding. The membrane interfering effect was distinct between different phospholipid compositions.

Conclusion

We found that Melectin may serve as a new potential template in the battle against multidrug resistance, and our study indicated that there are promising prospects for medically applicable drugs based on AMPs.

Mechanistic Landscape of Membrane-Permeabilizing Peptides

Membrane permeabilizing peptides (MPPs) are as ubiquitous as the lipid bilayer membranes they act upon. Produced by all forms of life, most membrane permeabilizing peptides are used offensively or defensively against the membranes of other organisms. Just as nature has found many uses for them, translational scientists have worked for decades to design or optimize membrane permeabilizing peptides for applications in the laboratory and in the clinic ranging from antibacterial and antiviral therapy and prophylaxis to anticancer therapeutics and drug delivery. Here, we review the field of membrane permeabilizing peptides. We discuss the diversity of their sources and structures, the systems and methods used to measure their activities, and the behaviors that are observed. We discuss the fact that "mechanism" is not a discrete or a static entity for an MPP but rather the result of a heterogeneous and dynamic ensemble of structural states that vary in response to many different experimental conditions. This has led to an almost complete lack of discrete three-dimensional active structures among the thousands of known MPPs and a lack of useful or predictive sequence-structure-function relationship rules. Ultimately, we discuss how it may be more useful to think of membrane permeabilizing peptides mechanisms as broad regions of a mechanistic landscape rather than discrete molecular processes.

Parasitic Nematodes Exert Antimicrobial Activity and Benefit From Microbiota-Driven Support for Host Immune Regulation

Intestinal parasitic nematodes live in intimate contact with the host microbiota. Changes in the microbiome composition during nematode infection affect immune control of the parasites and shifts in the abundance of bacterial groups have been linked to the immunoregulatory potential of nematodes. Here we asked if the small intestinal parasite Heligmosomoides polygyrus produces factors with antimicrobial activity, senses its microbial environment and if the anti-nematode immune and regulatory responses are altered in mice devoid of gut microbes. We found that H. polygyrus excretory/secretory products exhibited antimicrobial activity against gram^+/− bacteria. Parasites from germ-free mice displayed alterations in gene expression, comprising factors with putative antimicrobial functions such as chitinase and lysozyme. Infected germ-free mice developed increased small intestinal Th2 responses coinciding with a reduction in local Foxp3⁺RORγt⁺ regulatory T cells and decreased parasite fecundity. Our data suggest that nematodes sense their microbial surrounding and have evolved factors that limit the outgrowth of certain microbes. Moreover, the parasites benefit from microbiota-driven immune regulatory circuits, as an increased ratio of intestinal Th2 effector to regulatory T cells coincides with reduced parasite fitness in germ-free mice.

The Intestinal Roundworm Ascaris suum Releases Antimicrobial Factors Which Interfere With Bacterial Growth and Biofilm Formation

Ascariasis is a widespread soil-transmitted helminth infection caused by the intestinal roundworm Ascaris lumbricoides in humans, and the closely related Ascaris suum in pigs. Progress has been made in understanding interactions between helminths and host immune cells, but less is known concerning the interactions of parasitic nematodes and the host microbiota. As the host microbiota represents the direct environment for intestinal helminths and thus a considerable challenge, we studied nematode products, including excretory-secretory products (ESP) and body fluid (BF), of A. suum to determine their antimicrobial activities. Antimicrobial activities against gram-positive and gram-negative bacterial strains were assessed by the radial diffusion assay, while effects on biofilm formation were assessed using the crystal violet static biofilm and macrocolony assays. In addition, bacterial neutralizing activity was studied by an agglutination assay. ESP from different A. suum life stages (in vitro-hatched L3, lung-stage L3, L4, and adult) as well as BF from adult males were analyzed by mass spectrometry. Several proteins and peptides with known and predicted roles in nematode immune defense were detected in ESP and BF samples, including members of A. suum antibacterial factors (ASABF) and cecropin antimicrobial peptide families, glycosyl hydrolase enzymes such as lysozyme, as well as c-type lectin domain-containing proteins. Native, unconcentrated nematode products from intestine-dwelling L4-stage larvae and adults displayed broad-spectrum antibacterial activity. Additionally, adult A. suum ESP interfered with biofilm formation by Escherichia coli, and caused bacterial agglutination. These results indicate that A. suum uses a variety of factors with broad-spectrum antibacterial activity to affirm itself within its microbe-rich environment in the gut.

Screening of Probiotic Candidates in Human Oral Bacteria for the Prevention of Dental Disease

The oral cavity in healthy subjects has a well-balanced microbiota that consists of more than 700 species. However, a disturbance of this balance, with an increase of harmful microbes and a decrease of beneficial microbes, causes oral disorders such as periodontal disease or dental caries. Nowadays, probiotics are expected to confer oral health benefits by modulating the oral microbiota. This study screened new probiotic candidates with potential oral health benefits and no harmful effects on the oral cavity. We screened 14 lactobacillus strains and 36 streptococcus strains out of 896 oral isolates derived from healthy subjects. These bacteria did not produce volatile sulfur compounds or water-insoluble glucan, had higher antibacterial activity against periodontal bacteria, and had higher adherence activity to oral epithelial cells or salivary-coated hydroxyapatite in vitro. We then evaluated the risk of primary cariogenicity and infective endocarditis of the selected oral isolates. As a result, Lactobacillus crispatus YIT 12319, Lactobacillus fermentum YIT 12320, Lactobacillus gasseri YIT 12321, and Streptococcus mitis YIT 12322 were selected because they showed no cariogenic potential in an artificial mouth system and a lower risk of experimental infective endocarditis in a rat model. These candidates are expected as new probiotics with potential oral health benefits and no adverse effects on general health.

Isolation and characterization of peptidoglycan recognition protein 1 from antler base of sika deer (Cervus nippon)

Peptidoglycan recognition proteins (PGRPs) are secreted innate immunity pattern recognition molecules. In this study, a new peptidoglycan recognition protein 1 named cnPGRP1 was isolated from an antler base of sika deer Cervus nippon. The antler base antimicrobial proteins (AAP) were subjected to consecutive chromatographic methods connected to Sephadex G-25 gel filtration column (CM) anion-exchange column, and RP-HPLC. The molecular weight of cnPGRP1 was 17.2 kDa under SDS-PAGE, and peptide mass fingerprint analysis by MALDI-TOF-MS as peptidoglycan recognition protein 1 matched to Dasypus novemcinctus. The matched amino acids sequences were RLYEIIQKWPHYRA. Both Gram-positive and Gram-negative bacteria can be killed by cnPGRP1 in the 50-250 μg/mL range through in vitro. Furthermore, cnPGRP1 has been found to bind Gram-positive bacteria, Gram-negative bacteria, and even fungus.

Alarin but not its alternative-splicing form, GALP (Galanin-like peptide) has antimicrobial activity

Alarin is an alternative-splicing form of GALP (galanin-like peptide). It shares only 5 conserved amino acids at the N-terminal region with GALP which is involved in a diverse range of normal brain functions. This study seeks to investigate whether alarin has additional functions due to its differences from GALP. Here, we have shown using a radial diffusion assay that alarin but not GALP inhibited the growth of Escherichia coli (strain ML-35). The conserved N-terminal region, however, remained essential for the antimicrobial activity of alarin as truncated peptides showed reduced killing effect. Moreover, alarin inhibited the growth of E. coli in a similar potency as human cathelicidin LL-37, a well-studied antimicrobial peptide. Electron microscopy further showed that alarin induced bacterial membrane blebbing but unlike LL-37, it did not cause hemolysis of erythrocytes. In addition, alarin is only active against the gram-negative bacteria, E. coli but not the gram-positive bacteria, Staphylococcus aureus. Thus, these data suggest that alarin has potentials as an antimicrobial and should be considered for the development in human therapeutics.

Two hits are better than one: membrane-active and DNA binding-related double-action mechanism of NK-18, a novel antimicrobial peptide derived from mammalian NK-lysin

The extensive use and misuse of antibiotics in medicine result in the emergence of multidrug-resistant bacteria, creating an urgent need for the development of new chemotherapeutic agents. Nowadays, antimicrobial peptides are widely recognized as a class of promising candidates with activity against multidrug-resistant bacteria. NK-18 is a truncated peptide derived from NK-Lysin, an effector of cytotoxic T cells and natural killer cells. In this study, we studied the antibacterial mechanism of action of NK-18. The results revealed that NK-18 has potent antibacterial activity against Escherichia coli and Staphylococcus aureus. According to our findings, NK-18 is membrane active and its target of action is not only the bacterial membrane but also the DNA in the cytoplasm. The double targets of NK-18 make it difficult for bacteria to generate resistance, which may present a new strategy to defend against multidrug-resistant bacteria and provide a new lead in the design of potent antimicrobial peptides with therapeutic application in the presence of increasing resistance to conventional antibiotics.

The N-terminal glycine-rich and cysteine-rich regions are essential for antimicrobial activity of crustinPm1 from the black tiger shrimp Penaeus monodon

An antimicrobial protein crustinPm1 from Penaeus monodon is a WAP domain-containing protein with an antimicrobial activity against Gram-positive bacteria but does not have antiproteinase activity. The lack of antiproteinase is speculated to be due to the P(1)' Met and/or the length of spacing between the conserved Cys2 and Cys3 while the antimicrobial activity may be due to the N-terminal Gly-rich and Cys-rich regions. In this study, the P(1)-P(1)' and the N-terminal Gly-rich and Cys-rich regions of crustinPm1 were mutated by amino acid substitution or deletion. Substitutions of P(1)-P(1)' from Pro-Pro to Leu-Leu, Leu-His, Leu-Met, Leu-Ala and P(1)' from Pro to Met did not make the protein inhibitory to subtilisin, trypsin, chymotrypsin and elastase. The mutations at P(1)-P(1)' positions in rcrustinPm1 had no effect on antibacterial activity. The WAP domain mutant with both Gly-rich and Cys-rich regions deleted did not exhibit antibacterial activity against Staphylococcus aureus while the deletion mutants of either Gly-rich or Cys-rich regions exhibited lower antibacterial activity than the wild type crustinPm1. Therefore, both Gly-rich and Cys-rich regions attached to a WAP domain are essential for efficient antibacterial activity of crustinPm1.

Peptides and proteins with antimicrobial activity

The increase of microbial resistance to antibiotics has led to a continuing search for newer and more effective drugs. Antimicrobial peptides are generally found in animals, plants, and microorganisms and are of great interest to medicine, pharmacology, and the food industry. These peptides are capable of inhibiting pathogenic microorganisms. They can attack parasites, while causing little or no harm to the host cells. The defensins are peptides found in granules in the polymorphonuclear neutrophils (PMNs) and are responsible for the defense of the organism. Several animal defensins, like dermaseptin, antileukoprotease, protegrin, and others, have had their activities and efficacy tested and been shown to be effective against bacteria, fungi, and protists; there are also specific defensins from invertebrates, e.g., drosomycin and heliomicin; from plants, e.g., the types A and B; and the bacteriocins, e.g., acrocin, marcescin, etc. The aim of the present work was to compile a comprehensive bibliographic review of the diverse potentially antimicrobial peptides in an effort to systematize the current knowledge on these substances as a contribution for further researches. The currently available bibliography does not give a holistic approach on this subject. The present work intends to show that the mechanism of defense represented by defensins is promising from the perspective of its application in the treatment of infectious diseases in human, animals and plants.

Toll-like receptor-4 (TLR4) mediates human beta-defensin-2 (HBD-2) induction in response to Chlamydia pneumoniae in mononuclear cells

Monocytes are pivotal effector cells of the innate immune system that are vital for recognizing and eliminating invasive microbial pathogens. When microbial products bind to pathogen-recognition receptors, monocytes are activated and release a broad array of cytokines and defensins that orchestrate the host innate and adaptive immune responses. The aim of the present study is to investigate whether Toll-like receptor-4 (TLR4) mediates human beta-defensin-2 (HBD-2) induction in response to Chlamydia pneumoniae in mononuclear cells. We showed that TLR4 is expressed in U937 cells and monocytes infected with viable microorganisms in a time-dependent fashion, while heat-inactivated microorganisms induced a lesser expression, albeit still significant, of TLR4 compared with viable organisms; flow cytometric analysis, in particular, revealed a higher level of TLR4 expression at 48 and 72 h postinfection. In addition, U937 cells and monocytes responded to C. pneumoniae in a TLR4-dependent manner with induction of mRNA and protein of the antimicrobial peptide HBD-2. The treatment of cells with TLR4-neutralizing antibody resulted in a decrease in C. pneumoniae-induced HBD-2 production. This study reveals that TLRs not only recognize ligands but also the types of effector molecules induced, namely, antimicrobial peptides. An understanding of the importance of the TLR-mediated antimicrobial mechanisms may provide new avenues for the development of therapeutic regimens aimed at activating the body's own defenses by stimulating TLR-dependent pathways.

Antibiotic resistance in clinical isolates of Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus does not impact sensitivity to human beta defensin 4

Antibiotic usage is essential for infection control but hastens emergence of antibiotic resistant microbes. In particular, Acinetobacter baumannii is an important pathogen because of its heightened ability to acquire drug resistance. The need for novel antibacterial agents led us to evaluate the sensitivity of drug-resistant bacteria to the antimicrobial activity of human beta defensin 4 (HBD-4). Clinical isolates of A. baumannii (N=14), Pseudomonas aeruginosa (N=15), and Staphylococcus aureus (N=20), including 10 methicillin-resistant (MRSA) isolates, were examined. All bacterial strains were susceptible to HBD-4 antimicrobial activity, with no correlation between antibiotic resistance and HBD-4 sensitivity. The results demonstrate that antibiotic resistant microorganisms, including MRSA, can be inhibited by HBD-4, which may represent an effective therapeutic agent for infections involving drug-resistant microorganisms.

Capsule polysaccharide is a bacterial decoy for antimicrobial peptides

Antimicrobial peptides (APs) are important host weapons against infections. Nearly all APs are cationic and their microbicidal action is initiated through interactions with the anionic bacterial surface. It is known that pathogens have developed countermeasures to resist these agents by reducing the negative charge of membranes, by active efflux and by proteolytic degradation. Here we uncover a new strategy of resistance based on the neutralization of the bactericidal activity of APs by anionic bacterial capsule polysaccharide (CPS). Purified CPSs from Klebsiella pneumoniae K2, Streptococcus pneumoniae serotype 3 and Pseudomonas aeruginosa increased the resistance to polymyxin B of an unencapsulated K. pneumoniae mutant. Furthermore, these CPSs increased the MICs of polymyxin B and human neutrophil alpha-defensin 1 (HNP-1) for unencapsulated K. pneumoniae, Escherichia coli and P. aeruginosa PAO1. Polymyxin B or HNP-1 released CPS from capsulated K. pneumoniae, S. pneumoniae serotype 3 and P. aeruginosa overexpressing CPS. Moreover, this material also reduced the bactericidal activity of APs. We postulate that APs may trigger in vivo the release of CPS, which in turn will protect bacteria against APs. We found that anionic CPSs, but not cationic or uncharged ones, blocked the bactericidal activity of APs by binding them, thereby reducing the amount of peptides reaching the bacterial surface. Supporting this, polycations inhibited such interaction and the bactericidal activity was restored. We postulate that trapping of APs by anionic CPSs is an additional selective virulence trait of these molecules, which could be considered as bacterial decoys for APs.

A gene delivery approach for antimicrobials: Expression of defensins

INTRODUCTION

Peptide antibiotics as new therapeutic agents are becoming a popular option to investigate due to their broad bacterial target selectivity and limited resistance problems. Although attractive, these new drug candidates have several limitations including low potency and delivery issues which face all peptides/proteins.

METHODS

In this study, we designed a plasmid expression system for human beta defensin 3. This sequence was cloned from a human epithelial lung cell into a CMV driven expression cassette. This expression plasmid was then evaluated for its ability to produce human-beta defensin 3 with the use of the non-viral transfection agent, polyethylenimine (PEI).

RESULTS

The results indicate the expression cassette was transcriptionally active in HEK 293 cells, as measured by RT-PCR and that a beta defensin peptide was produced by the cells as confirmed by Western blot. The biological activity of the peptide was confirmed against both gram negative E. coli and gram positive Bacillus species using in vitro screening.

CONCLUSION

Both the cultured media as well as the transfected cell lysate demonstrated biological activity demonstrating the peptide is also secreted.

Staphylococcus aureus evasion of innate antimicrobial defense

Bacterial pathogens colonize human body surfaces soon after birth. In order to survive the constant threat of invasion and infection, the human innate immune system has evolved several efficient mechanisms to prevent harmful microorganisms from traversing epithelial barriers. These include cationic antimicrobial peptides (CAMPs) such as defensins and the cathelicidin LL-37, bacteriolytic enzymes such as lysozyme, antimicrobial fatty acids, toxic oxygen- or nitrogen-containing molecules, the bacteriolytic complement components and further mechanisms with indirect impacts on bacterial multiplication. Staphylococcus aureus is an important human commensal and pathogen. In order to successfully establish an infection, S. aureus has evolved several mechanisms to resist the innate immune system. In this review, we focus on the mechanisms employed by S. aureus to achieve protection against antimicrobial host defense molecules with special emphasis on CAMPs. Lessons from recent studies on antimicrobial host defense molecules and cognate bacterial resistance adaptation should help in the development of more sustainable anti-infective compounds.

Plectasin has antibacterial activity and no affect on cell viability or IL-8 production

Animals and plants express endogenous peptide antibiotics called defensins. Defensins show broad-spectrum antimicrobial activity, even against bacteria that have resistance to conventional antibiotics, which has made them viable candidates for new antibiotics. However, human defensins have failed to reach the market because of their cytotoxic effects and non-antimicrobial bioactivities. Plectasin is a defensin that has shown promise but has not had its potentially negative effects clarified. To address this issue, we examined plectasin's cytotoxicity in human cells using an AlamarBlue reduction assay, its interleukin (IL)-8-inducing capacity using real-time PCR and ELISA, and measured its MIC against bacteria. We confirmed that plectasin has specific antibacterial activity against Streptococcus pneumoniae. Plectasin showed no cytotoxicity to A549 cells, normal human bronchial epithelial cells, or lung fibroblasts, and it did not induce IL-8 transcription or production in A549 cells. Our results suggest that plectasin could be an inoffensive alternative antibiotic for clinical application.

In vitro susceptibility of Staphylococcus aureus to thrombin-induced platelet microbicidal protein-1 (tPMP-1) is influenced by cell membrane phospholipid composition and asymmetry

Thrombin-induced platelet microbicidal proteins (e.g. tPMP-1) are small cationic peptides released from mammalian platelets. As the cytoplasmic membrane (CM) is a primary target of tPMPs, distinct CM characteristics are likely to affect the cells' susceptibility profiles. In Staphylococcus aureus, CM surface charge and hydrophobicity are principally determined by the content and distribution of its three major phospholipid (PL) constituents: negatively charged phosphatidylglycerol (PG) and cardiolipin (CL) and positively charged lysyl-PG (LPG). PL composition profiles, and inner vs outer CM leaflet PL distributions, were compared in an isogenic tPMP-susceptible (tPMP(S)) and -resistant (tPMP(R)) S. aureus strain pair (ISP479C vs ISP479R respectively). All PLs were asymmetrically distributed between the outer and inner CM leaflets in both strains. However, in ISP479R, the outer CM leaflet content of LPG was significantly increased vs ISP479C (27.3+/-11.0 % vs 18.6+/-7.0 % respectively; P=0.05). This observation correlated with reduced binding of the cationic proteins cytochrome c, poly-L-lysine, tPMP-1 and the tPMP-1-mimetic peptide, RP1, to tPMP-1(R) whole cells and to model liposomal CMs with LPG content and distribution similar to that of tPMP-1(R) strains. Collectively, selected CM parameters correlated with reduced staphylocidal capacities of tPMP-1 against certain S. aureus strains, including relative increases in outer CM leaflet positive charge and reduced surface binding of cationic molecules. These findings offer new insights into mechanisms of antimicrobial peptide susceptibility and resistance in S. aureus.

Identification of antimicrobial activity from goat cervical epithelium

1. In mammals, antimicrobial peptides are present in epithelial cells of the respiratory, gastrointestinal and urinogenital tracts. In the present study, we report the identification and partial characterization of an antimicrobial peptide in extracts prepared from goat cervical epithelial tissue. 2. The bioactivity, as determined by radial and disc diffusion assays, was identified in a peptide of molecular mass 4.5 kDa purified by cation exchange and gel filtration techniques. The purified peptide exhibited antibacterial activity against Escherichia coli (Gram-negative) as well as Bacillus subtilis (Gram-positive) bacteria. 3. The minimum inhibitory concentration of the peptide estimated by liquid broth assay for E. coli and B. subtilis suspensions was 31 and 50 microg/mL, respectively, a result implying that the peptide is more efficient in inhibiting Gram-negative than Gram-positive bacteria. 4. Because the peptide has no spermicidal activity, we propose that it is responsible for protecting the female genital tract against bacteria. 5. Whether the peptide has potentials for use in the cryopreservation, storage and transport of semen remains to be determined.

Antimicrobial activity of truncated alpha-defensin (human neutrophil peptide (HNP)-1) analogues without disulphide bridges

Antimicrobial peptides play an important role in host defence, particularly in the oral cavity where there is constant challenge by microorganisms. The alpha-defensin antimicrobial peptides comprise 30-50% of the total protein in the azurophilic granules of human neutrophils, the most abundant of which is human neutrophil peptide 1 (HNP-1). Despite its antimicrobial activity, a limiting factor in the potential therapeutic use of HNP-1 is its chemical synthesis with the correct disulphide topology. In the present study, we synthesised a range of truncated defensin analogues lacking disulphide bridges. All the analogues were modelled on the C-terminal region of HNP-1 and their antimicrobial activity was tested against a range of microorganisms, including oral pathogens. Although there was variability in the antimicrobial activity of the truncated analogues synthesised, a truncated peptide named 2Abz(23)S(29) displayed a broad spectrum of antibacterial activity, effectively killing all the bacterial strains tested. The finding that truncated peptides, modelled on the C-terminal beta-hairpin region of HNP-1 but lacking disulphide bridges, display antimicrobial activity could aid their potential use in therapeutic interventions.

Antimicrobial activity of omwaprin, a new member of the waprin family of snake venom proteins

We have isolated and characterized omwaprin, a 50-amino-acid cationic protein from the venom of inland taipan (Oxyuranus microlepidotus). It is a new member of the waprin family of snake venom proteins. A synthetic gene was designed and constructed for expressing the recombinant protein in Escherichia coli. Recombinant omwaprin was used for carrying out functional analyses. The protein is non-toxic to Swiss albino mice at doses of up to 10 mg/kg when administered intraperitoneally. However, it shows selective and dose-dependant antibacterial activity against Gram-positive bacteria. The minimum inhibitory doses were in the range 2-10 microg for selected species of bacteria in radial diffusion assays. The antibacterial activity is salt-tolerant up to 350 mM NaCl. However, omwaprin lost its antibacterial activity upon reduction and alkylation of its cysteine residues, or upon deletion of six N-terminal amino acid residues, four of which are positively charged. These observations indicate that the three-dimensional structure constrained by four disulfide bonds and the N-terminal residues are essential for its activity. The mechanism of action is via membrane disruption, as shown by scanning electron microscopy. Importantly, omwaprin lacks haemolytic activity on human erythrocytes. This demonstrates the specificity of omwaprin for bacterial membranes. Unlike other reported WAP (whey acidic protein) domain-containing antibacterial proteins, including elafin, EPPIN (epididymal proteinase inhibitor), SWAM1 and SWAM2 [single WAP (whey acidic protein) motif proteins 1 and 2] and SLPI (secretory leucocyte proteinase inhibitor), omwaprin shows species-specific activity on the Gram-positive bacteria tested.

Expression of Human Beta Defensin 4 in Genetically Modified Keratinocytes Enhances Antimicrobial Activity

Defensins are cationic peptides of the innate host defense system with antimicrobial activity against many of the microorganisms commonly found in burn units. Beta defensins are variably expressed in the epithelia of skin and other organs. Human beta defensin 4 reportedly has antimicrobial activity against Pseudomonas aeruginosa and is not normally expressed in intact skin. Genetic modification was used to ectopically express human beta defensin 4 in cultured primary epidermal keratinocytes. Keratinocytes expressing human beta defensin 4 showed significantly elevated antimicrobial activity against clinically-isolated P. aeruginosa compared with controls. These results suggest that genetic modification of keratinocytes can increase their resistance to microbial contamination. Bioengineered skin replacements containing human beta defensin 4-modified keratinocytes may be useful for transplantation to contaminated burn wounds.

α-Defensins from blood leukocytes of the monkey Papio hamadryas

Three antimicrobial peptides named PHD1-3 (Papio hamadryas defensin) have been isolated from hamadryas baboon blood leukocytes using preparative electrophoresis and reverse-phase HPLC. The primary structures of these peptides have been determined by automated Edman degradation and mass-spectrometry. The results suggest that the peptides belong to the alpha-defensin family. Structural homology analysis reveals that among alpha-defensins from other animal species, PHD3 is the most closely related to RMAD5 (rhesus macaque alpha-defensin) (90% homology) from rhesus macaque leukocytes and also highly similar to human alpha-defensin HD5 (60% homology), which is produced by intestinal Paneth cells. The homology of PHD3 with human neutrophil alpha-defensin HNP1 (human natural peptide) was 30%. The primary structures of PHD1 and PHD2 are most similar to RED1 (rhesus enteral defensin), one of six enteral alpha-defensins of rhesus monkeys. PHD1-3 have been shown to be active against the Gram-positive bacteria Listeria monocytogenes and Staphylococcus aureus, the Gram-negative bacterium Escherichia coli, and the fungus Candida albicans, similarly to the human HNP1 defensin.

Antimicrobial activities of human beta-defensins against Bacillus species

Natural defences in the human body function to protect us from numerous environmental toxins and exposure to potential harmful biological agents. An important frontline defence is antimicrobial peptides. These peptides occur at environmental interfaces and serve to limit bacterial invasion. There has been little work comparing specific peptides as potential antimicrobial compounds. In this study, we evaluated the antimicrobial activity of peptides from the human beta-defensin (HBD) family against four species of Bacillus, chosen as models for Bacillus anthracis, a potential bioweapon. The impact of peptide concentration, sequence and protein binding was evaluated on their biological activity. The results indicated that HBD-3 was the most biologically active against Bacillus subtilis and Bacillus licheniformis, whilst HBD-2 was found to be most active against Bacillus cereus and Bacillus thuringiensis. Moreover, the antimicrobial activity of the peptides was directly related to peptide concentration and indirectly related to albumin concentration (i.e. protein binding).

Isolation of human beta-defensin-4 in lung tissue and its increase in lower respiratory tract infection

BACKGROUND

Human beta-defensin-4 (hBD-4), a new member of the beta-defensin family, was discovered by an analysis of the genomic sequence. The objective of this study was to clarify hBD-4 expression in human lung tissue, along with the inducible expression in response to infectious stimuli, localization, and antimicrobial activities of hBD-4 peptides. We also investigated the participation of hBD-4 in chronic lower respiratory tract infections (LRTI) by measuring the concentrations of hBD-4 peptides in human bronchial epithelial lining fluid (ELF).

METHODS

The antimicrobial activity of synthetic hBD-4 peptides against E. coli and P. aeruginosa was measured by radial diffusion and colony count assays. We identified hBD-4 in homogenated human lung tissue by reverse-phase high-performance liquid chromatography coupled with a radioimmunoassay (RIA). Localization of hBD-4 was studied through immunohistochemical analysis (IHC). We investigated the effects of lipopolysaccharide (LPS) on hBD-4 expression and its release from small airway epithelial cells (SAEC). We collected ELF from patients with chronic LRTI using bronchoscopic microsampling to measure hBD-4 concentrations by RIA.

RESULTS

hBD-4 exhibited salt-sensitive antimicrobial activity against P. aeruginosa. We detected the presence of hBD-4 peptides in human lung tissue. IHC demonstrated the localization of hBD-4-producing cells in bronchial and bronchiolar epithelium. The levels of hBD-4 peptides released from LPS-treated SAECs were higher than those of untreated control cells. ELF hBD-4 was detectable in 4 of 6 patients with chronic LRTI, while the amounts in controls were all below the detectable level.

CONCLUSION

This study suggested that hBD-4 plays a significant role in the innate immunity of the lower respiratory tract.

Functional interrelationships between cell membrane and cell wall in antimicrobial peptide-mediated killing of Staphylococcus aureus

Perturbation of the Staphylococcus aureus cytoplasmic membrane (CM) is felt to play a key role in the microbicidal mechanism of many antimicrobial peptides (APs). However, it is not established whether membrane permeabilization (MP) alone is sufficient to kill susceptible staphylococci or if the cell wall (CW) and/or intracellular targets contribute to AP-induced lethality. We hypothesized that the relationships between MP and killing may differ for distinct APs. In this study, we investigated the association between AP-induced MP and lethality in S. aureus whole cells versus CW-free protoplasts, and in comparison to the MP of liposomes modeled after whole CMs in terms of phospholipid composition, fluidity and charge. Four APs with different structure-activity relationships were examined: thrombin-induced platelet microbicidal protein 1 (tPMP-1), human neutrophil protein 1 (hNP-1), gramicidin D, and polymyxin B. MP was quantified fluorometrically by calcein release. All APs tested, except polymyxin B, caused concentration-dependent MP and killing of whole cells, but not of protoplasts. The reduced AP susceptibility of protoplasts was associated with increased cardiolipin and lysyl-phosphatidylglycerol content and reduced fluidity of their CMs. However, liposomal MP induced by tPMP-1, hNP-1, and gramicidin D paralleled that of whole cells. Collectively, these results indicate that (i) structurally distinct APs likely exert their staphylocidal effects by differing mechanisms, (ii) MP is not the sole event leading to AP-induced staphylocidal activity, (iii) a complex interrelationship exists between the CM and CW in AP-induced killing, and (iv) liposomes modeled upon whole cell or protoplast CMs can recapitulate the respective susceptibilities to killing by distinct APs.

Histatin-derived peptides: potential agents to treat localised infections

Histatins are a family of histidine-rich, cationic peptides composed of up to 38 amino acids. They are secreted by the salivary glands of humans and some subhuman primates and are thought to be part of the host defence system in the oral cavity. Histatins exhibit in vitro activity against both bacteria and yeast, common to other antimicrobial peptides. Because of these activities, histatin-based peptides could play an important role in the treatment and prevention of infectious diseases. A 12 amino acid amidated fragment of histatin 5, designated P-113, has been identified as the smallest fragment that retains antimicrobial activity comparable to the parent compound. Animal studies and human clinical trials showed that P-113 has potential in preventing the development of gingivitis, with no adverse side effects. Histatin peptides also could be used for other therapeutic applications in which the infection is localised and accessible via topical delivery, such as treatment of candidiasis (thrush) and mucositis in the oral cavity, skin infections and treatment of lung infections afflicting cystic fibrosis patients.

Antibacterial activity and specificity of the six human {alpha}-defensins

We developed a kinetic, 96-well turbidimetric procedure that is capable of testing the antimicrobial properties of six human alpha-defensins concurrently on a single microplate. The defensins were prepared by solid-phase peptide synthesis and tested against gram-positive bacteria (Staphylococcus aureus and Bacillus cereus) and gram-negative bacteria (Enterobacter aerogenes and Escherichia coli). Analysis of the growth curves provided virtual lethal doses (vLDs) equivalent to conventional 50% lethal doses (LD(50)s), LD(90)s, LD(99)s, and LD(99.9)s obtained from colony counts. On the basis of their respective vLD(90)s and vLD(99)s, the relative potencies of human myeloid alpha-defensins against S. aureus were HNP2 > HNP1 > HNP3 > HNP4. In contrast, their relative potencies against E. coli and E. aerogenes were HNP4 > HNP2 > HNP1 = HNP3. HD5 was as effective as HNP2 against S. aureus and as effective as HNP4 against the gram-negative bacteria in our panel. HD6 showed little or no activity against any of the bacteria in our panel, including B. cereus, which was highly susceptible to the other five alpha-defensins. The assay described provides a quantitative, precise, and economical way to study the antimicrobial activities of host-defense peptides. Its use has clarified the relative potencies of human alpha-defensins and raised intriguing questions about the in vivo function(s) of HD6.

Expression of human beta-defensins HBD-1, HBD-2, and HBD-3 in cultured keratinocytes and skin substitutes

Defensins are effector molecules of the innate host defense system with antimicrobial activity against a variety of pathogens, including microorganisms commonly found in burn units. beta-Defensins are variably expressed in the epithelia of skin and other organs. Cultured skin substitutes (CSS) grafted to burn wounds lack a vascular plexus and are therefore more susceptible to microbial contamination than split thickness skin autograft. To investigate whether beta-defensins can contribute to host defense in CSS, we examined expression of human beta-defensins HBD-1, HBD-2, and HBD-3 in cultured keratinocytes and CSS from uninjured donors and burn patients. HBD-1 was expressed in all keratinocyte strains analyzed. HBD-2 expression in keratinocyte monolayers was highly variable but did not correlate with burn injury. HBD-3 was expressed at variable levels in all but one keratinocyte strain. CSS were prepared from two donors that lacked expression of HBD-2 in keratinocyte monolayers. All three genes were readily detected in CSS from both donors, suggesting up-regulation of HBD-2 and HBD-3. In sections of CSS, HBD-1, HBD-2, and HBD-3 proteins were localized to distinct epidermal regions. We conclude that beta-defensins can potentially contribute to innate immunity in CSS, but their levels may be too low to prevent contamination after grafting.

High-level expression and purification of a recombinant hBD-1 fused to LMM protein in Escherichia coli

In this work, we present the production of an active 43 aa recombinant human beta-defensin-1 (rhBD-1(43)) in Escherichia coli AD202 cells using specific pLMM1-rhBD-1 expression system. Unique solubility properties of the C-terminal fragment of light meromyosin (LMM) allowed us to overcome foreseeable problems with isolation procedures and toxicity caused by rhBD-1 to the host organism. As a result, the majority of fusion protein (LMM-rhBD-1(43)) was obtained in the soluble state, isolated by a low salt-high salt treatment of total cell protein. The rhBD-1(43) was cleaved from the fusion with Protease 4 and purified on CM Sepharose Fast Flow column with the yield of approximately 1 mg rhBD-1(43) from 6 g of wet weight cells. Purified rhBD-1(43) showed antimicrobial activity against E. coli ML-35p at a concentration of 129 microM. The procedure of rhBD-1 expression and purification we present can provide a reliable and simple method for production of different cationic peptides for biological studies.

Treatment of infected wounds with the antimicrobial peptide D2A21

BACKGROUND

Infected wounds impose a significantly negative effect on patient care and recovery, as infection hinders normal wound healing, resulting in increased patient morbidity and mortality. More attention is being focused on addressing the problem of multidrug-resistant bacteria and the staggering costs and consequences resulting from this. Recently, newly evaluated antimicrobial peptides have been shown to be active against a wide variety of bacteria in in vitro studies. This study evaluates the use of a particular antimicrobial peptide, D2A21 (Pittsburgh, PA), to combat infection in an acutely infected wound model.

METHODS

Forty-eight Wistar rats were used to compare the effects of D2A21 to control vehicle, silver sulfadiazine (SSD), and Sulfamylon in this model. Two 1.5 x 1.5-cm full-thickness defects were created on the rat dorsum and were subsequently inoculated with 108 Pseudomonas aeruginosa. Animals underwent daily treatment with either D2A21 gel, control vehicle, SSD, or Sulfamylon. Animals were evaluated for survival differences.

RESULTS

Survival analysis at 21 days for the different treatment groups were as follows: 100% for the D2A21-treated animals, 50% for control-treated animals, 83% for Sulfamylon-treated animals, and 33% for SSD-treated animals.

CONCLUSION

D2A21 antimicrobial peptide demonstrates significant activity compared with controls and standards of therapy. The promising effect of this topical peptide is clearly evident as shown by this study, and its further investigation as a potential agent in the fight against infected or chronic wounds is warranted.

Activation of a Src-dependent Raf-MEK1/2-ERK signaling pathway is required for IL-1alpha-induced upregulation of beta-defensin 2 in human middle ear epithelial cells

beta-defensin 2 is produced by a variety of epithelial cell types in the body and exhibits potent antimicrobial activity against a variety of pathogens, including the bacteria that are most commonly associated with otitis media (OM). The human beta-defensin 2 (hBD-2) gene is an NF-kappa B regulated gene and a variety of proinflammatory stimuli can induce its expression. Although the presence of molecules of innate immunity such as lysozyme and lactoferrin has been demonstrated in the middle ear, to date there have been no reports on the expression of beta-defensin 2. In the present study, we demonstrate that beta-defensin 2 is expressed in the middle ear mucosa of humans and rats. We also show that it is expressed in a human middle ear epithelial cell line and that its expression is induced by proinflammatory stimuli such as interleukin 1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF-alpha), and lipopolysaccharide (LPS). Moreover, we demonstrate that the transcriptional activation of hBD-2 gene by IL-1 alpha is mediated through an Src-dependent Raf-MEK1/2-ERK signaling pathway.

ADP ribosylation of human neutrophil peptide-1 regulates its biological properties

In human airways, epithelial cells lining the lumen and intraluminal cells (e.g., polymorphonuclear cells) participate in the innate immune response. These cells secrete or express on their surfaces arginine-specific ADP ribosyltransferases. Defensins, antimicrobial proteins secreted by immune cells, are arginine-rich, leading us to hypothesize that ADP ribosylation could modify their biological activities. We found that an arginine-specific ADP ribosyltransferase-1 present on airway epithelial cells modifies Arg-14 of alpha defensin-1. ADP-ribosylated defensin-1 had decreased antimicrobial and cytotoxic activities but still stimulated T cell chemotaxis and IL-8 release from A549 cells. Further, ADP-ribosylated defensin-1 inhibited cytotoxic and antimicrobial activities of unmodified defensin-1. We identified ADP-ribosylated defensin-1 in bronchoalveolar lavage fluid from smokers but not from nonsmokers, confirming its existence in vivo. Thus, airway mono-ADP-ribosyltransferases could have an important regulatory role in the innate immune response through modification of alpha defensin-1 and perhaps other basic molecules, with alteration of their biological properties.

Improvement in burn wound infection and survival with antimicrobial peptide D2A21 (Demegel)

Naturally occurring antimicrobial peptides have been discovered in both plants and animals. Many of these peptides demonstrate impaired activity or cytotoxicity when applied exogenously. Synthetically engineered antimicrobial peptides have been designed to increase potency and activity against bacteria and fungus yet remain noncytotoxic. The antimicrobial peptide D2A21 (Demegel) has already demonstrated significant activity in vitro against many common hospital pathogens. The purpose of this study was to evaluate the effects of D2A21 in an in vivo infected burn-wound model, examining both quantitative cultures of the wound and survival of the animal. Forty-four Wistar rats were subjected to a 23 percent total body surface area scald burn. Pseudomonas aeruginosa was administered topically with 108 organisms and wounds were then evaluated at day 1, 2, or 3 for eschar and subeschar muscle quantitative culture. The experimental group was treated daily with 1.5% topical D2A21. The control group was treated with control gel. A second group of Wistar rats (n = 14) were burned and given a 107 inoculum of the same Pseudomonas and evaluated to 14 days for survival and weight changes. This group was subdivided into rats receiving either topical D2A21 or control base daily. The quantitative biopsy results demonstrated that D2A21-treated wounds had no bacterial growth in burn eschar at day 2 or 3, whereas control animals demonstrated growth at greater than 105 organisms by day 2. Subeschar muscle cultures also demonstrated significantly less bacterial invasion compared with controls on each day tested. D2A21-treated animals had an 85.7 percent survival compared with 0 percent survival in controls. Furthermore, the D2A21-treated groups demonstrated maintenance of body weights, whereas controls had significant weight loss with time. In conclusion, D2A21 demonstrates significant antibacterial activity against Pseudomonas, sterilizing burn eschar and decreasing subeschar bacterial load, allowing for a markedly significant improvement in survival in this infected burn-wound model.

Attachment of Staphylococcus aureus to eukaryotic cells and experimental pitfalls in staphylococcal adherence assays: a critical appraisal

Staphylococcus aureus is a bacterial species with pathogenic potential to both humans and animals. The primary natural niche is said to be the human vestibulum nasi from where bacterial cells may spread to the environment or additional anatomical sites such as the perineum or the hands, where residence is usually transient. Apparently, S. aureus is capable of a precise and balanced interaction with specific types of eukaryotic nasal cells. Although a wide variety of important bacterial ligands and possible eukaryote receptors have been described, the precise mechanisms leading to persistent bacterial colonization and, even more importantly, associated infection have not yet been elucidated in detail. This may be a consequence of the fact that most of the adherence factors have been studied individually in simplified in vitro systems, not taking the complexity of multi-factorial in vivo cell-cell interactions into account. An overall scheme of the initial and sequential interactions leading to S. aureus colonization of eukaryotic cell surfaces has not yet emerged. This review concisely describes the current state of affairs in the multi-disciplinary field of staphylococcal adherence research. Specific emphasis is placed upon the pros and cons of the various artificial, mostly in vitro models employed to study the interaction between bacterial and human or animal cells.

Quantitative determination of gelatinase activity among enterococci

Gelatinase, hemolysin and aggregation substance have all been reported to be virulence factors of enterococci. In this study, gelatinase production was investigated in isolates of Enterococcus faecalis (n=93), E. faecium (n=49) and E. avium (n=36) recovered from hospitalized patients. Gelatinase was detected in 45% of E. faecalis isolates, but could not be detected in E. faecium and E. avium. Gelatinase activity was then measured by radial diffusion for the 42 gelatinase-positive E. faecalis isolates. To convert gelatinase activity into proteinase K activity, a standard curve was produced by placing different concentrations of proteinase K into wells in the gelatine plate. Gelatinase activity per E. faecalis colony ranged from 2.6 x 10(-7) to 2.2 x 10(-5) microg/ml, proportionate to the activity of proteinase K. An approximately 84-fold difference in gelatinase concentration was observed between the colony producing the highest amount and that producing the lowest amount. This method may be useful for determining the virulence of given isolates in relation to gelatinase production as it is quick, easy and inexpensive to perform.

Anticandida activity is retained in P-113, a 12-amino-acid fragment of histatin 5

Through the analysis of a series of 25 peptides composed of various portions of the histatin 5 sequence, we have identified P-113, a 12-amino-acid fragment of histatin 5, as the smallest fragment that retains anticandidal activity comparable to that of the parent compound. Amidation of the P-113 C terminus increased the anticandidal activity of P-113 approximately twofold. The three histidine residues could be exchanged for three hydrophobic residues, with the fragment retaining anticandidal activity. However, the change of two or more of the five basic (lysine and arginine) residues to uncharged residues resulted in a substantial loss of anticandidal activity. A synthetic D-amino-acid analogue, P-113D, was as active against Candida albicans as the L-amino-acid form. In vitro MIC tests in low-ionic-strength medium showed that P-113 has potent activity against Candida albicans, Candida glabrata, Candida parapsilosis, and Candida tropicalis. These results identify P-113 as a potential antimicrobial agent in the treatment of oral candidiasis.

Nisin A depletes intracellular ATP and acts in bactericidal manner against Mycobacterium smegmatis

Nisin is a bacteriocin produced by many strains of Lactococcus lactis. This study examined the effect of nisin on Mycobacterium smegmatis, a non-pathogenic species of Mycobacterium. Nisin had a minimum inhibitory concentration of 8.0 micrograms ml-1 and a minimum inhibitory dose of 7.5 micrograms ml-1 against Myco. smegmatis. Treatment with 25.0 micrograms ml-1 nisin caused partial inhibition of Myco smegmatis; the survivors were nisin-sensitive when tested in a separate experiment. Mycobacterium smegmatis cells exposed to 50.0 micrograms ml-1 of nisin, lost their viability. the effect of nisin on the growth of Myco. smegmatis was both time- and concentration-dependent. Nisin (10.0 micrograms ml-1) caused 97.7 +/- 2.0% reduction in internal ATP and leakage of intracellular ATP out of Myco. smegmatis cells after several hours of treatment. These data suggest that nisin inhibits Myco. smegmatis by the same mechanism by which it inhibits other bacteria and warrants further investigation as a possible antitubercular agent.

Protegrin-1: a broad-spectrum, rapidly microbicidal peptide with in vivo activity

Protegrin-1 (PG-1) is a cysteine-rich, 18-residue beta-sheet peptide isolated from porcine leukocytes with antimicrobial activity against a broad range of microorganisms. The MICs of PG-1 against representative gram-positive and gram-negative bacteria ranged from 0.12 to 2 microg/ml. At these levels, PG-1 was rapidly bactericidal in vitro, reducing the number of viable CFU of either methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa by more than three log units in less than 15 min. Resistance to PG-1 did not develop after 11 subculturings of P. aeruginosa or 18 subcultures of MRSA in Mueller-Hinton broth containing PG-1 at one-half the MIC. Under similar conditions of serial passage, the MICs of norfloxacin and gentamicin against P. aeruginosa increased 10 and 190 times, respectively. Similarly, the MIC of norfloxacin against MRSA increased 85 times. Immunocompetent mice inoculated intraperitoneally (i.p.) with P. aeruginosa or S. aureus exhibited 93 to 100% mortality in the vehicle control group compared with 0 to 27% mortality in animals that received a single i.p. injection of PG-1 (0.5 mg/kg of body weight). Mice inoculated with S. aureus by intravenous (i.v.) injection and dosed 0 to 60 min later with a single i.v. injection of PG-1 (5 mg/kg) had a mortality of 7 to 33%, compared to a mortality of 73 to 93% in the vehicle controls. In leukopenic mice inoculated i.v. with vancomycin-resistant Enterococcus faecium, mortality was 87% in the vehicle control group and 33% in animals that received a single i.v. injection of PG-1 (2.5 mg/kg). Taken together, these data indicate that PG-1 has potential for use as an antimicrobial agent in the treatment of local or systemic infections caused by clinically relevant pathogens.