Killing of Fusobacterium nucleatum, Porphyromonas gingivalis and Prevotella intermedia by protegrins

Conceptual Perspectives: Bacterial Antimicrobial Peptide Induction as a Novel Strategy for Symbiosis with the Human Host

Human beta defensins (hBDs) are small cationic peptides, expressed in mucosal epithelia and important agents of innate immunity, act as antimicrobial and chemotactic agents at mucosal barriers. In this perspective, we present evidence supporting a novel strategy by which the oral bacterium Fusobacterium nucleatum induces hBDs and other antimicrobial peptides (AMPs) in normal human oral epithelial cells (HOECs) and thereby protects them from other microbial pathogens. The findings stress (1) the physiological importance of hBDs, (2) that this strategy may be a mechanism that contributes to homeostasis and health in body sites constantly challenged with bacteria and (3) that novel properties identified in commensal bacteria could, one day, be harnessed as new probiotic strategies to combat colonization of opportunistic pathogens. With that in mind, we highlight and review the discovery and characterization of a novel lipo-protein, FAD-I (FusobacteriumAssociated Defensin Inducer) associated with the outer membrane of F. nucleatum that may act as a homeostatic agent by activating endogenous AMPs to re-equilibrate a dysregulated microenvironment. FAD-I has the potential to reduce dysbiosis-driven diseases at a time when resistance to antibiotics is increasing. We therefore postulate that FAD-I may offer a new paradigm in immunoregulatory therapeutics to bolster host innate defense of vulnerable mucosae, while maintaining physiologically responsive states of inflammation.

Mirror image proteins

Proteins composed entirely of unnatural d-amino acids and the achiral amino acid glycine are mirror image forms of their native l-protein counterparts. Recent advances in chemical protein synthesis afford unique and facile synthetic access to domain-sized mirror image d-proteins, enabling protein research to be conducted through 'the looking glass' and in a way previously unattainable. d-Proteins can facilitate structure determination of their native l-forms that are difficult to crystallize (racemic X-ray crystallography); d-proteins can serve as the bait for library screening to ultimately yield pharmacologically superior d-peptide/d-protein therapeutics (mirror-image phage display); d-proteins can also be used as a powerful mechanistic tool for probing molecular events in biology. This review examines recent progress in the application of mirror image proteins to structural biology, drug discovery, and immunology.

All-d-Enantiomer of β-Amyloid Peptide Forms Ion Channels in Lipid Bilayers

Alzheimer's disease (AD) is the most common type of senile dementia in aging populations. Amyloid β (Aβ)-mediated dysregulation of ionic homeostasis is the prevailing underlying mechanism leading to synaptic degeneration and neuronal death. Aβ-dependent ionic dysregulation most likely occurs either directly via unregulated ionic transport through the membrane or indirectly via Aβ binding to cell membrane receptors and subsequent opening of existing ion channels or transporters. Receptor binding is expected to involve a high degree of stereospecificity. Here, we investigated whether an Aβ peptide enantiomer, whose entire sequence consists of d-amino acids, can form ion-conducting channels; these channels can directly mediate Aβ effects even in the absence of receptor-peptide interactions. Using complementary approaches of planar lipid bilayer (PLB) electrophysiological recordings and molecular dynamics (MD) simulations, we show that the d-Aβ isomer exhibits ion conductance behavior in the bilayer indistinguishable from that described earlier for the l-Aβ isomer. The d isomer forms channel-like pores with heterogeneous ionic conductance similar to the l-Aβ isomer channels, and the d-isomer channel conductance is blocked by Zn(2+), a known blocker of l-Aβ isomer channels. MD simulations further verify formation of β-barrel-like Aβ channels with d- and l-isomers, illustrating that both d- and l-Aβ barrels can conduct cations. The calculated values of the single-channel conductance are approximately in the range of the experimental values. These findings are in agreement with amyloids forming Ca(2+) leaking, unregulated channels in AD, and suggest that Aβ toxicity is mediated through a receptor-independent, nonstereoselective mechanism.

Through the looking glass, mechanistic insights from enantiomeric human defensins

Despite the small size and conserved tertiary structure of defensins, little is known at a molecular level about the basis of their functional versatility. For insight into the mechanism(s) of defensin function, we prepared enantiomeric pairs of four human defensins, HNP1, HNP4, HD5, and HBD2, and studied their killing of bacteria, inhibition of anthrax lethal factor, and binding to HIV-1 gp120. Unstructured HNP1, HD5, and HBD3 and several other human alpha- and beta-defensins were also examined. Crystallographic analysis showed a plane of symmetry that related (L)HNP1 and (D)HNP1 to each other. Either d-enantiomerization or linearization significantly impaired the ability of HNP1 and HD5 to kill Staphylococcus aureus but not Escherichia coli. In contrast, (L)HNP4 and (D)HNP4 were equally bactericidal against both bacteria. d-Enantiomers were generally weaker inhibitors or binders of lethal factor and gp120 than their respective native, all-l forms, although activity differences were modest, particularly for HNP4. A strong correlation existed among these different functions. Our data indicate: (a) that HNP1 and HD5 kill E. coli by a process that is mechanistically distinct from their actions that kill S. aureus and (b) that chiral molecular recognition is not a stringent prerequisite for other functions of these defensins, including their ability to inhibit lethal factor and bind gp120 of HIV-1.

Porcine host defense peptides: expanding repertoire and functions

Host defense peptides (HDPs) are a large group of innate immune effectors that are also termed antimicrobial peptides. Because of the rapid progress that has been made in completing several animal genomes, many HDPs have been systemically defined using bioinformatic analysis and partially characterized using reverse genomic approaches. In pigs, about 30 HDPs have been identified and partially characterized relative to structure and function. Antimicrobial activity of porcine HDPs has been extensively evaluated against a broad spectrum of microorganisms in vitro and evaluated for their protective role in vivo. Increasing evidence indicates that HDPs are functionally differentiated during posttranslational and postsecretory processing, and that the structural units for antimicrobial and immunoregulatory functions are separate. These findings suggest promising new avenues for therapeutic drug design based on HDPs, including porcine HDPs. This review summarizes and discusses advances in porcine HDPs research during the last decade with an emphasis on the rapidly expanding profiles and biological functions.

Effects of cations and pH on antimicrobial activity of thanatin and s-thanatin against Escherichia coli ATCC25922 and B. subtilis ATCC 21332

This study analyzes the in vitro effects of cations and pH on antimicrobial activity of thanatin and s-thanatin against Escherichia coli ATCC25922 and B. subtilis ATCC21332. Thanatin and s-thanatin were synthesized by the solid-phase method using a model 432A synthesizer. The bacterial strains tested included two antibiotic-susceptible strains of Escherichia coli ATCC25922 and B. subtilis ATCC21332. Susceptibility determinations were carried out either in a variety of cation concentrations or in pH conditions from pH 5 to pH 8. NaCl or KCl was added to the media to final concentrations of 0, 10, 50, 100, 200, and 500 mM, whereas CaCl(2) and MgCl(2) were added to the media to final concentrations of 0, 1, 2, 5, 10, and 20 mM. The antimicrobial activity of thanatin and s-thanatin against Escherichia coli ATCC25922 and B. subtilis ATCC21332 decreased, as indicated by the increasing minimal inhibitory concentrations (MICs) of both peptides with increasing concentrations of Na(+)/K(+)/Ca(2+)/Mg(2+). Both peptides lost their activities at 500 mM Na(+)/K(+) but retained them at 20 mM Ca(2+)/Mg(2+). Both peptides have MICs that are not significantly different at a variety of pH levels, with the antimicrobial activity slightly higher in neutral or slightly basic media than under acidic conditions. The antimicrobial peptides thanatin and s-thanatin, which have an anti-parallel beta-sheet constrained by disulfide bonds, were salt sensitive against both Gram-positive and Gram-negative pathogens in vitro. Determining the reason why the thanatins are salt sensitive would be useful to provide an understanding of how thanatin and s-thanatin kill bacteria. Further investigation of the antimicrobial properties of these peptides is warranted.

Factors affecting antimicrobial activity of MUC7 12-mer, a human salivary mucin-derived peptide

Background

MUC7 12-mer (RKSYKCLHKRCR), a cationic antimicrobial peptide derived from the human low-molecular-weight salivary mucin MUC7, possesses potent antimicrobial activity in vitro. In order to evaluate the potential therapeutic application of the MUC7 12-mer, we examined the effects of mono- and divalent cations, EDTA, pH, and temperature on its antimicrobial activity.

Methods

Minimal Inhibitory Concentrations (MICs) were determined using a liquid growth inhibition assay in 96-well microtiter plates. MUC7 12-mer was added at concentrations of 1.56–50 μM. MICs were determined at three endpoints: MIC-0, MIC-1, and MIC-2 (the lowest drug concentration showing 10%, 25% and 50% of growth, respectively). To examine the effect of salts or EDTA, a checkerboard microdilution technique was used. Fractional inhibitory concentration index (FICi) was calculated on the basis of MIC-0. The viability of microbial cells treated with MUC7 12-mer in the presence of sodium or potassium was also determined by killing assay or flow cytometry.

Results

The MICs of MUC7 12-mer against organisms tested ranged from 6.25–50 μM. For C. albicans, antagonism (FICi 4.5) was observed for the combination of MUC7 12-mer and calcium; however, there was synergism (FICi 0.22) between MUC7 12-mer and EDTA, and the synergism was retained in the presence of calcium at its physiological concentration (1–2 mM). No antagonism but additivity or indifference (FICi 0.55–2.5) was observed for the combination of MUC7 12-mer and each K⁺, Na⁺, Mg²⁺, or Zn²⁺. MUC7 12-mer peptide (at 25 μM) also exerted killing activity in the presence of NaCl, (up to 25 mM for C. albicans and up to 150 mM for E. coli, a physiological concentration of sodium in the oral cavity and serum, respectively) and retained candidacidal activity in the presence of KCl (up to 40 mM). The peptide exhibited higher inhibitory activity against C. albicans at pH 7, 8, and 9 than at pH 5 and 6, and temperature up to 60°C did not affect the activity.

Conclusion

MUC7 12-mer peptide is effective anticandidal agent at physiological concentrations of variety of ions in the oral cavity. These results suggest that, especially in combination with EDTA, it could potentially be applied as an alternative therapeutic agent for the treatment of human oral candidiasis.

Impact of anatomic site on growth, efflux-pump expression, cell structure, and stress responsiveness of Bacteroides fragilis

This study investigated whether B. fragilis from various human sites acquired stable traits enabling it to express certain efflux pumps (EPs), adopt a particular cell structure, and tolerate certain stressors. Isolates from blood, abscess, and stool (n = 11 each) were investigated. Bacteria from various sites portrayed different ultrastructres and EP expression. Blood isolates were tolerant to nutrient limitation and stool isolates to NaCl and bile salt stress. Stressors significantly increased EP expression. These data demonstrate that (1) B. fragilis acquires stable traits from various in vivo microenvironments; (2) that EPs are involved in stress responsiveness; and (3) that EP expression is tightly controlled and site dependent.

Bile salts enhance bacterial co-aggregation, bacterial-intestinal epithelial cell adhesion, biofilm formation and antimicrobial resistance of Bacteroides fragilis

Bacteroides fragilis is the most common anaerobic bacterium isolated from human intestinal tract infections. Before B. fragilis interacts with the intestinal epithelial cells, it is exposed to bile salts at physiological concentrations of 0.1-1.3%. The aim of this study was to determine how pre-treatment with bile salts affected B. fragilis cells and their interaction with intestinal epithelial cells. B. fragilis NCTC9343 was treated with conjugated bile salts (BSC) or non-conjugated bile salts (BSM). Cellular ultrastructure was assessed by electron microscopy, gene expression was quantified by comparative quantitative real-time RT-PCR. Adhesion to the HT-29 human intestinal cell line and to PVC microtitre plates (biofilm formation) was determined. Exposure to 0.15% BSC or BSM resulted in overproduction of fimbria-like appendages and outer membrane vesicles, and increased expression of genes encoding RND-type efflux pumps and the major outer membrane protein, OmpA. Bile salt-treated bacteria had increased resistance to structurally unrelated antimicrobial agents and showed a significant increase in bacterial co-aggregation, adhesion to intestinal epithelial cells and biofilm formation. These data suggest that bile salts could enhance intestinal colonization by B. fragilis via several mechanisms, and could therefore be significant to host-pathogen interactions.

Mechanisms of decreased susceptibility to beta-defensins by Treponema denticola

Treponema denticola, a periodontal pathogen, is relatively resistant to human beta-defensins, which are small cationic antimicrobial peptides produced by a number of cells, including the gingival epithelium. Using two independent methods, we previously demonstrated that T. denticola proteases are not responsible for decreased vulnerability to defensins. In this study, we confirmed that the major outer membrane protease, dentilisin, is not responsible for T. denticola insensitivity to defensins and examined several other possible mechanisms, including reduced binding to the bacterial surface and efflux pump activity. It has been suggested that some bacteria mask their surfaces with serum proteins. T. denticola grown in a serum-free medium did not exhibit increased susceptibility to human beta-defensin 2 and 3 (hbetaD-2 and hbetaD-3, respectively), suggesting that cloaking of the outer surface with host proteins is not involved in defensin resistance. Nonetheless, we demonstrated that T. denticola binds significantly less hbetaD-2 and -3 than susceptible organisms bind, suggesting that the unusual outer membrane composition of T. denticola may discourage cationic peptide binding. Efflux pumps have been shown to mediate resistance to antibiotics and cationic peptides in other bacteria, and their role in T. denticola's relative resistance to beta-defensins was investigated. Three inhibitors of bacterial ATP-binding cassette (ABC) efflux pumps had no effect on T. denticola's susceptibility to hbetaD-2 or -3. In contrast, a proton motive force inhibitor, carbonyl cyanide 3-chlorophenylhydrazone, increased the susceptibility of T. denticola to killing by hbetaD-3, demonstrating a potential role for efflux pumps (other than ABC pumps) in resistance to this peptide. Our data suggest that the combination of decreased defensin binding and efflux of any peptide which enters the cytoplasm may explain T. denticola's relative resistance to human beta-defensins.

Induction of {beta}-defensin resistance in the oral anaerobe Porphyromonas gingivalis

Induction of resistance of oral anaerobes to the effects of human beta-defensin 1 (hbetaD-1) to hbetaD-4 was investigated by pretreating cells with either sublethal levels of defensins or environmental factors, followed by a challenge with lethal levels of defensins. Cultures of Porphyromonas gingivalis were (i) pretreated with defensins at 1 ng/ml, (ii) heated to 42 degrees C (heat stress), (iii) exposed to normal atmosphere (oxidative stress), or (iv) exposed to 1 mM hydrogen peroxide (peroxide stress). Samples (10 microl) were distributed among the wells of sterile 384-well plates containing hbetaD-1 to -4 (100 microg/ml). Plates were incubated at 37 degrees C for 36 h in an anaerobe chamber. Growth inhibition was determined by a system that measures the total nucleic acid of a sample with a DNA binding dye. The MICs of the four defensins for P. gingivalis were 3 to 12 microg/ml. We found that sublethal levels of the defensins and heat and peroxide stress, but not oxidative stress, induced resistance to 100 microg of defensin per ml in P. gingivalis. Resistance induced by sublethal levels of hbetaD-2 lasted 90 min, and the resistance induced by each defensin was effective against the other three. Multiple strains exposed to hbetaD-2 all evidenced resistance induction. Defensin resistance is vital to the pathogenic potential of several human pathogens. This is the first report describing the induction of defensin resistance in the oral periodontal pathogen P. gingivalis. Such resistance may have an effect on the ability of oral pathogens to persist in the mouth and to withstand innate human immunity.

Resistance to human beta-defensins is common among oral treponemes

BACKGROUND/AIMS

Oral treponemes are implicated in the pathogenesis of periodontal disease. We have previously shown that Treponema denticola ATCC type strains and strain GM-1 are resistant to killing by human beta-defensins (hbetaD)-1 and -2. We hypothesize that resistance to beta-defensins is a common feature of oral treponemes, which allows colonization and persistence in the oral cavity. In this study, we tested additional isolates of T. denticola, as well as six other species of treponemes, for resistance to hbetaD-1, -2 and -3. We also examined the four ATCC strains of T. denticola and strain GM-1 for resistance to hbetaD-3.

METHODS

Resistance was determined by motility and Alamar Blue assays for metabolic activity.

RESULTS

All T. denticola strains tested were resistant to hbetaD-1, -2 and -3, with the exception of strain Ambigua, which was sensitive to hbetaD-2 and -3. All other treponemes except Treponema vincentii were resistant to hbetaD-1. Treponema pectinovorum was sensitive to hbetaD-2, while T. vincentii, T. pectinovorum and Treponema maltophilum were sensitive to hbetaD-3. Escherichia coli was used as a control organism and was killed by all three defensins.

CONCLUSION

Resistance to the constitutively expressed hbetaD-1 may assist treponemes in initial colonization of epithelial surfaces, while resistance to the inducible hbetaD-2 and -3 would allow some treponemes to survive in active periodontal lesions.

Susceptibility of oral bacteria to an antimicrobial decapeptide

Naturally occurring antimicrobial peptides have emerged as alternative classes of antimicrobials. In general, these antimicrobial peptides exhibit selectivity for prokaryotes and minimize the problems of engendering microbial resistance. As an alternative method to search for more effective broad-spectrum peptide antimicrobials, investigators have developed peptide libraries by using synthetic combinatorial technology. A novel decapeptide, KKVVFKVKFK (KSL), has been identified that shows a broad range of antibacterial activity. The purpose of this study was to test the efficacy of this antimicrobial peptide in killing selected strains of oral pathogens and resident saliva bacteria collected from human subjects. Cytotoxic activity of KSL against mammalian cells and the structural features of this decapeptide were also investigated, the latter by using two-dimensional NMR in aqueous and DMSO solutions. MICs of KSL for the majority of oral bacteria tested in vitro ranged from 3 to 100 microg ml(-1). Minimal bactericidal concentrations of KSL were, in general, within one to two dilutions of the MICs. KSL exhibited an ED(99) (the dose at which 99 % killing was observed after 15 min at 37 degrees C) of 6.25 microg ml(-1) against selected strains of Lactobacillus salivarius, Streptococcus mutans, Streptococcus gordonii and Actinobacillus actinomycetemcomitans. In addition, KSL damaged bacterial cell membranes and caused 1.05 log units reduction of viability counts of saliva bacteria. In vitro toxicity studies showed that KSL, at concentrations up to 1 mg ml(-1), did not induce cell death or compromise the membrane integrity of human gingival fibroblasts. NMR studies suggest that KSL adopts an alpha-helical structure in DMSO solution, which mimics the polar aprotic membrane environment, whereas it remains unstructured in aqueous medium. This study shows that KSL may be a useful antimicrobial agent for inhibiting the growth of oral bacteria that are associated with caries development and early plaque formation.

Activity of Novispirin G-10, a novel antimicrobial peptide against Chlamydia trachomatis and vaginosis-associated bacteria

We tested the activity of Novispirin G-10, a novel antimicrobial alpha-helical octadecapeptide structurally related to cathelicidins and other innate immunity peptides, against Chlamydia trachomatis serovars L2, D, and E and three organisms associated with bacterial vaginosis (BV). The peptide's activity against C. trachomatis was measured in 48-h shell vial assays with McCoy cell targets. Exposure to 100 micro g/ml of Novispirin G-10 reduced the infectivity of serovars D and E by 99.4-100% and serovar L2 by 91.7-99.1%. At the same concentration of 100 micro g/ml, Novispirin G-10 rapidly killed >99% of Mobiluncus curtisii, Gardnerella vaginalis, and Prevotella bivia, in standard colony-forming unit (CFU) assays. Given its simple structure and relative lack of cytotoxic and hemolytic activity, Novispirin G-10 may be a useful component of microbicide preparations designed to prevent chlamydial infection and/or remediate the abnormal vaginal flora associated with BV.

Antimicrobial activity of magainin analogues against anaerobic oral pathogens

Magainins are a family of potent antimicrobial cationic peptides that possess antimicrobial activity against a wide range of target organisms. In this study, the antimicrobial activity of synthetic magainin-mimetic compounds MSI-751 and MSI-774 was investigated against the periodontal pathogens Porphyromonas gingivalis, Fusobacterium nucleatum, Actinobacillus actinomycetemcomitans, Eikenella corrodens, Prevotella loescheii and Prevotella intermedia. P. gingivalis was more susceptible to MSI-751 than to MSI-774, whereas the other oral pathogens showed little difference in susceptibility to the two compounds. MSI-751 exhibited a rapid, dose-dependent bactericidal effect on P. gingivalis. Electron microscopy of MSI-751-treated P. gingivalis revealed intact cell wall vesicles devoid of cell contents, suggesting perturbation of the cytoplasmic membrane by this compound, perhaps equivalent to formation of membrane-disruptive ion channels by magainin peptides. These studies demonstrate that synthetic magainin derivatives exhibit antimicrobial activity against oral pathogens by disruption of cell membrane integrity.

Treponema denticola is resistant to human beta-defensins

Spirochetes, including Treponema denticola, are implicated in the pathogenesis of periodontal disease. Because T. denticola lacks lipopolysaccharides that serve as targets for human beta-defensin (h beta D) binding, we postulated that T. denticola would resist killing by h beta D. We showed that T. denticola is resistant to h beta D-1 and -2. Protease inhibitors did not enhance killing of T. denticola by h beta D-2, suggesting that degradation of h beta D-2 by treponemal proteases is not a major factor in T. denticola resistance.

Binding of protegrin-1 to Pseudomonas aeruginosa and Burkholderia cepacia

BACKGROUND

Pseudomonas aeruginosa and Burkholderia cepacia infections of cystic fibrosis patients' lungs are often resistant to conventional antibiotic therapy. Protegrins are antimicrobial peptides with potent activity against many bacteria, including P. aeruginosa. The present study evaluates the correlation between protegrin-1 (PG-1) sensitivity/resistance and protegrin binding in P. aeruginosa and B. cepacia.

METHODS

The PG-1 sensitivity/resistance and PG-1 binding properties of P. aeruginosa and B. cepacia were assessed using radial diffusion assays, radioiodinated PG-1, and surface plasmon resonance (BiaCore).

RESULTS

The six P. aeruginosa strains examined were very sensitive to PG-1, exhibiting minimal active concentrations from 0.0625-0.5 microg/ml in radial diffusion assays. In contrast, all five B. cepacia strains examined were greater than 10-fold to 100-fold more resistant, with minimal active concentrations ranging from 6-10 microg/ml. When incubated with a radioiodinated variant of PG-1, a sensitive P. aeruginosa strain bound considerably more protegrin molecules per cell than a resistant B. cepacia strain. Binding/diffusion and surface plasmon resonance assays revealed that isolated lipopolysaccharide (LPS) and lipid A from the sensitive P. aeruginosa strains bound PG-1 more effectively than LPS and lipid A from resistant B. cepacia strains.

CONCLUSION

These findings support the hypothesis that the relative resistance of B. cepacia to protegrin is due to a reduced number of PG-1 binding sites on the lipid A moiety of its LPS.

Structural features and biological activities of the cathelicidin-derived antimicrobial peptides

Cathelicidins are a numerous group of mammalian proteins that carry diverse antimicrobial peptides at the C-terminus of a highly conserved preproregion. These peptides, which become active when released from the proregion, display a remarkable variety of sizes, sequences, and structures, and in fact comprise representatives of all the structural groups in which the known antimicrobial peptides have been classified. Most of the cathelicidin-derived peptides exert a broad spectrum and potent antimicrobial activity and also bind to lipopolysaccharide and neutralize its effects. In addition, some of them have recently been shown to exert other activities and might participate in host defense also by virtue of their ability to induce expression of molecules involved in a variety of biological processes. This review is aimed at providing a general overview of the cathelicidins and of the peptides derived therefrom, with emphasis on aspects such as structure, biological activities in vitro and in vivo, and structure/activity relationship studies.

Sensitivity of Actinobacillus actinomycetemcomitans and Capnocytophaga spp. to the bactericidal action of LL-37: a cathelicidin found in human leukocytes and epithelium

The bactericidal activity of synthetic LL-37, a cathelicidin, was assessed against Actinobacillus actinomycetemcomitans (three strains) and Capnocytophaga spp. (three strains). All strains were sensitive to LL-37, and exhibited 99% effective dose of 7.5-to-11.6 micrograms/ml. An amidated form of LL-37, pentamide-37, killed with about the same efficacy as LL-37. Partial inhibition of killing was noted at physiologic concentrations of NaCl, and complete inhibition was observed at 400 mM NaCl. At approximately the 99% effective dose--i.e., 10 micrograms/ml--LL-37 also lost activity against A. actinomycetemcomitans in the presence of native or heat-inactivated 10-15% normal human AB serum. Pentamide-37 was less sensitive to serum inhibition than LL-37. In conclusion, certain oral, gram-negative bacteria are sensitive to the bactericidal activity of LL-37 at low concentrations of serum and salt, a condition likely to be found within the membrane-delimited phagolysosome. Modified forms of LL-37, such as pentamide-37, may be more suitable for future therapeutic application in the presence of serum.

Animal antimicrobial peptides: an overview

Antibiotic peptides are a key component of the innate immune systems of most multicellular organisms. Despite broad divergences in sequence and taxonomy, most antibiotic peptides share a common mechanism of action, i.e., membrane permeabilization of the pathogen. This review provides a general introduction to the subject, with emphasis on aspects such as structural types, post-translational modifications, mode of action or mechanisms of resistance. Some of these questions are treated in depth in other reviews in this issue. The review also discusses the role of antimicrobial peptides in nature, including several pathological conditions, as well as recent accounts of their application at the preclinical level.

Activities of synthetic hybrid peptides against anaerobic bacteria: aspects of methodology and stability

The increasing problem of antibiotic resistance among pathogenic bacteria requires development of new antimicrobial agents. One line of investigation is the synthesis of antimicrobial hybrid peptides. The aim of the present investigation was to determine the in vitro activities of 16 cecropin-melittin hybrid peptides (CAMEL analogues) against 60 anaerobic bacterial strains, to compare their activities with those of seven clinically used antimicrobial agents, and to compare different methods for anaerobic susceptibility testing of these peptides. The stability of one of the peptides, temporin B, with different stereoisomeric configurations was investigated in a fecal milieu. The CAMEL analogues showed antimicrobial activity against the anaerobic bacteria, with MICs ranging from 0.125 to 32 microg/ml. The overall activities (the MICs at which 90% of isolates are inhibited) of the CAMEL analogues against anaerobic bacteria were mainly inferior to those of imipenem, clindamycin, and piperacillin but were equal to or superior to those of metronidazole, cefoxitin, ciprofloxacin, and chloramphenicol. The agarose dilution method was found to be an accurate method for the testing of large numbers of bacterial strains. The D isomer of temporin B was inactivated more slowly in feces than the L isomer. This study shows that the CAMEL analogues are potential agents for the treatment of anaerobic infections.