Antimicrobial activity of three tick defensins and four mammalian cathelicidin-derived synthetic peptides against Lyme disease spirochetes and bacteria isolated from the midgut

Identification of Genes Associated with Resistance to Persulcatusin, a Tick Defensin from Ixodes persulcatus

Antimicrobial peptides (AMPs) are present in a wide range of plants, animals, and microorganisms. Since AMPs are characterized by their effectiveness against emergent antibiotic-resistant bacteria, they are attracting attention as next-generation antimicrobial compounds that could solve the problem of drug-resistant bacteria. Persulcatusin (IP), an antibacterial peptide derived from the hard tick Ixodes persulcatus, shows high antibacterial activity against various Gram- positive bacteria as well as multidrug-resistant bacteria. However, reports on the antibacterial action and resistance mechanisms of IP are scarce. In this study, we spontaneously generated mutants showing increased a minimum inhibitory concentration (MIC) of IP and analyzed their cross-resistance to other AMPs and antibiotics. We also used fluorescent probes to investigate the target of IP activity by evaluating IP-induced damage to the bacterial cytoplasmic membrane. Our findings suggest that the antimicrobial activity of IP on bacterial cytoplasmic membranes occurs via a mechanism of action different from that of known AMPs. Furthermore, we screened for mutants with high susceptibility to IP using a transposon mutant library and identified 16 genes involved in IP resistance. Our results indicate that IP, like other AMPs, depolarizes the bacterial cytoplasmic membrane, but it may also alter membrane structure and inhibit cell-wall synthesis.

What do we know about the microbiome of I. ricinus?

I. ricinus is an obligate hematophagous parasitic arthropod that is responsible for the transmission of a wide range of zoonotic pathogens including spirochetes of the genus Borrelia, Rickettsia spp., C. burnetii, Anaplasma phagocytophilum and Francisella tularensis, which are part the tick´s microbiome. Most of the studies focus on "pathogens" and only very few elucidate the role of "non-pathogenic" symbiotic microorganisms in I. ricinus. While most of the members of the microbiome are leading an intracellular lifestyle, they are able to complement tick´s nutrition and stress response having a great impact on tick´s survival and transmission of pathogens. The composition of the tick´s microbiome is not consistent and can be tied to the environment, tick species, developmental stage, or specific organ or tissue. Ovarian tissue harbors a stable microbiome consisting mainly but not exclusively of endosymbiotic bacteria, while the microbiome of the digestive system is rather unstable, and together with salivary glands, is mostly comprised of pathogens. The most prevalent endosymbionts found in ticks are Rickettsia spp., Ricketsiella spp., Coxiella-like and Francisella-like endosymbionts, Spiroplasma spp. and Candidatus Midichloria spp. Since microorganisms can modify ticks' behavior, such as mobility, feeding or saliva production, which results in increased survival rates, we aimed to elucidate the potential, tight relationship, and interaction between bacteria of the I. ricinus microbiome. Here we show that endosymbionts including Coxiella-like spp., can provide I. ricinus with different types of vitamin B (B2, B6, B7, B9) essential for eukaryotic organisms. Furthermore, we hypothesize that survival of Wolbachia spp., or the bacterial pathogen A. phagocytophilum can be supported by the tick itself since coinfection with symbiotic Spiroplasma ixodetis provides I. ricinus with complete metabolic pathway of folate biosynthesis necessary for DNA synthesis and cell division. Manipulation of tick´s endosymbiotic microbiome could present a perspective way of I. ricinus control and regulation of spread of emerging bacterial pathogens.

Microbiome analysis of the midguts of different developmental stages of Argas persicus in China

Argas persicus is an ectoparasite of poultry. The bacterial community structure and the pathogenic bacteria associated with different developmental stages of A. persicus have implications for control. Argas persicus were collected from chickens in the city of Jiuquan in Gansu, China. Bacterial DNA was extracted from the midgut contents of blood engorged larvae, nymphs and adult females. The V3-V4 hypervariable regions of 16S rRNA genes were sequenced using the IonS5™XL platform. Identification of Rickettsia spp. and detection of Coxiella burnetii were performed using PCR on target genes. The bacterial diversity within larvae was the highest and the bacterial diversity within nymphs was greater than that of adults. At different classification levels, seven bacterial phyla were common phyla, 27 genera were common genera, and 18 species were common species in the three samples. At the phylum level, Proteobacteria showed a marked predominance in all samples. Rickettsia, Stenotrophomonas, Spiroplasma, and Coxiella were the dominant bacteria at the genus level. The Rickettsia species in A. persicus was identified as Rickettsia hoogstraalii and the Coxiella species was identified as a Coxiella-like endosymbiont. Additionally, some bacterial species such as Pseudomonas geniculata, Sphingomonas koreensis, and Acinetobacter haemolyticus were reported here for the first time in A. persicus.

Relative contributions of different substrates to soil N2O emission and their responses to N addition in a temperate forest

With increasing nitrogen (N) deposition, soil nitrous oxide (N₂O) emission is expected to increase, causing positive feedback to global warming. However, the substrates of soil N₂O emission, especially their responses to N addition, are still unclear. Here, we conducted an in situ ¹⁵N tracing experiment to study the substrates of N₂O (i.e., ammonium-derived, nitrate-derived and organic N-derived N₂O emission) under N addition treatment in a temperate forest in northeast China. Nitrate derived N₂O through denitrification contributed most to the total N₂O emission, pointing to the importance of denitrification under ambient N deposition. NH₄NO₃ addition of 50 kg N ha^-1 yr^-1 significantly increased organic N derived N₂O on the 6th day after N addition, which suggests that heterotrophic nitrification may be the dominating process with higher N deposition rate. However, because soil pH and the examined functional genes did not change after N addition, future studies should be carried out to understand if the increase of heterotrophic nitrification is transient. Our study emphasizes the role of organic N pool in soil N₂O emissions, highlighting the importance of considering the heterotrophic nitrification process while studying soil N cycling or modeling soil N₂O emission.

A bovine myeloid antimicrobial peptide (BMAP-28) and its analogs kill pan-drug-resistant Acinetobacter baumannii by interacting with outer membrane protein A (OmpA)

Antimicrobial peptides (AMPs) exhibit multiple activities against bacteria and fungi. A bovine myeloid antimicrobial peptide (BMAP-28) belongs to the cathelicidin-derived AMPs and has antimicrobial activity. Due to the rapidly increasing number of infections and outbreaks caused by pan-drug-resistant Acinetobacter baumannii (PDRAB), we sought to determine whether BMAP-28 and its 4 analog peptides (A837, A838, A839, and A840) have antimicrobial activity against PDRAB. Furthermore, we clarified the possible mechanism of inhibition by which of BMAP-28 acts against PDRAB. In the current study, we examined the inhibitory effect of BMAP-28 and its 4 analog peptides on the growth of PDRAB through minimal inhibitory concentration (MIC) analysis and short time killing assays. We also evaluated the effects of BMAP-28 and its analogs on the bacterial cell surface through the use of field emission scanning electron microscopy (FE-SEM). In order to determine the inhibitory mechanism of BMAP-28, we examined the interaction between BMAP-28 and outer membrane proteins (OMPs), especially the interaction between BMAP-28 and A. baumannii OmpA (AbOmpA), which is the main component of OMPs, by using a quartz crystal microbalance (QCM). BMAP-28 and its 4 analogs were effective in inhibiting the growth of PDRAB and had rapid killing ability. BMAP-28 showed exceptionally strong and rapid inhibitory effects on PDRAB when compared to the other peptides and was also shown to cause damage to the cell surface of PDRAB. Moreover, QCM analysis provided evidence of potential interaction between BMAP-28 and AbOmpA. These data indicate that BMAP-28 is a promising candidate for the treatment of PDRAB infections and that its inhibitory effects were related with its binding to AbOmpA.

Plasticity in early immune evasion strategies of a bacterial pathogen

Borrelia burgdorferi is one of the few extracellular pathogens capable of establishing persistent infection in mammals. The mechanisms that sustain long-term survival of this bacterium are largely unknown. Here we report a unique innate immune evasion strategy of B. burgdorferi, orchestrated by a surface protein annotated as BBA57, through its modulation of multiple spirochete virulent determinants. BBA57 function is critical for early infection but largely redundant for later stages of spirochetal persistence, either in mammals or in ticks. The protein influences host IFN responses as well as suppresses multiple host microbicidal activities involving serum complement, neutrophils, and antimicrobial peptides. We also discovered a remarkable plasticity in BBA57-mediated spirochete immune evasion strategy because its loss, although resulting in near clearance of pathogens at the inoculum site, triggers nonheritable adaptive changes that exclude detectable nucleotide alterations in the genome but incorporate transcriptional reprograming events. Understanding the malleability in spirochetal immune evasion mechanisms that ensures their host persistence is critical for the development of novel therapeutic and preventive approaches to combat long-term infections like Lyme borreliosis.

Antiplasmodial activity of tick defensins in a mouse model of malaria

Malaria is a mosquito-borne disease affecting millions of people mainly in Sub-Saharan Africa, Asia and some South American countries. Drug resistance to first-line antimalarial drugs (e.g. chloroquine, sulfadoxine-pyrimethamine and artemisinin) is a major constrain in malaria control. Antimicrobial peptides (AMPs) have shown promising results in controlling Plasmodium spp. parasitemia in in vitro and in vivo models of infection. Defensins are AMPs that act primarily by disrupting the integrity of cell membranes of invasive microbes. We previously showed that defensins from the tick Ixodes ricinus inhibited significantly the growth of P. falciparum in vitro, a property that was conserved during evolution. Here, we tested the activity of three I. ricinus defensins against P. chabaudi in mice. A single dose of defensin (120 μl of 1 mg/ml solution) was administered intravenously to P. chabaudi-infected mice, and the parasitemia was followed for 24 h post-treatment. Defensin treatment inhibited significantly the replication (measured as increases in parasitemia) of P. chabaudi after 1 h and 12 h of treatment. Furthermore, defensin injection was not associated with toxicity. These results agreed with the previous report of antiplasmodial activity of tick defensins against P. falciparum in vitro and justify further studies for the use of tick defensins to control malaria.

Activity of tick antimicrobial peptide from Ixodes persulcatus (persulcatusin) against cell membranes of drug-resistant Staphylococcus aureus

Persulcatusin (IP), which is an antimicrobial peptide found in Ixodes persulcatus midgut, is active against Gram-positive bacteria such as Staphylococcus aureus. Multidrug-resistant bacteria in particular methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA) are a worldwide clinical concern. In the present study, to explore the potential of IP as a new agent against multidrug-resistant S. aureus infections, we evaluated the antimicrobial activity of IP against multidrug-resistant S. aureus strains by MIC₉₀, morphological observation with scanning electron microscope (SEM), and the calcein leakage assay of membrane integrity. Among the six antimicrobial peptides used in this study, IP exhibited the lowest MIC₉₀ values for both vancomycin-susceptible and -resistant S. aureus strains. The IP MIC₉₀ against a VISA strain was equivalent to vancomycin, while the MIC₉₀ against VRSA was relatively low. SEM observations indicated that bacterial cells exposed to IP were crumpled and showed prominent structural changes. Moreover, IP influenced the cell membranes of both MRSA and VRSA in a mere 5 min, leading to leakage of the preloaded calcein. Although a VISA strain was resistant to the action of IP on cell membrane, the MIC₉₀ of IP was lower than that of Nisin, suggesting that IP had another bactericidal mechanism in addition to cell membrane attack. Our results indicate that the synthetic tick antimicrobial peptide, IP exhibits strong antibacterial activity against multidrug-resistant S. aureus strains, including VRSA, via both cell membrane attack and another unknown mechanism. IP represents a promising candidate for a new anti-VRSA therapy.

Inhibitory effect of BMAP-28 on Leptospiral Lipopolysaccharide-Induced TLR2-Dependent Immune Response in Bovine Cells

Background

Bovine leptospirosis is a widespread zoonotic disease, leading to serious economic losses in animal production and causing potential hazards to human health. Leptospiral lipopolysaccharide (L-LPS) plays an important role in leptospirosis pathogenicity.

Objectives

With respect to L-LPS endotoxin-like activity, we examined bovine immune response to L-LPS and the inhibitory ability of bovine myeloid antimicrobial peptide-28 (BMAP-28) against L-LPS-induced immune activation in bovine cells.

Materials and Methods

In this study, L-LPS-induced proinflammatory cytokine production in bovine cells was quantitatively measured with real-time PCR and ELISA, and we determined which cell membrane receptors (toll-like receptor [TLR]2 and TLR4) played a major role. In addition, the ability of BMAP-28 to inhibit L-LPS-induced endotoxin-like immune activation in bovine cells was determined by the decrease in cytokine secretion.

Results

L-LPS showed the ability to induce cytokine production in bovine cells, and its induction was TLR2-dependent. BMAP-28 was used to inhibit L-LPS-induced endotoxin-like activity. The function of BMAP-28 was to inhibit LPS-induced TLR2 expression and cytokine production.

Conclusions

In this study, the L-LPS immune response of bovine cells was significant, indicating that TLR2 is the predominant receptor for L-LPS. Due to L-LPS endotoxin-like activity, we found a strategy through using BMAP-28 to prevent L-LPS-induced TLR2-dependent immune activation in bovine cells.

Functional structure and antimicrobial activity of persulcatusin, an antimicrobial peptide from the hard tick Ixodes persulcatus

Background

Antimicrobial peptides (AMPs) are considered promising candidates for the development of novel anti-infective agents. In arthropods such as ticks, AMPs form the first line of defense against pathogens in the innate immune response. Persulcatusin (IP) was found in the Ixodes persulcatus midgut, and its amino acid sequence was reported. However, the complete structure of IP has not been identified. We evaluated the relation between structural features and antimicrobial activity of IP, and its potential as a new anti-methicillin-resistant Staphylococcus aureus (MRSA) agent.

Methods

The structure of IP was predicted using homology modeling and molecular dynamics. IP and other tick AMPs were synthesized using a solid-phase method and purified by high-performance liquid chromatography. Methicillin-susceptible S. aureus (MSSA) and MRSA were used for the minimum inhibitory concentration (MIC) test and short-time killing assay of IP and other tick peptides. The influence of IP on mammalian fibroblasts and colon epithelial cells and each cell DNA and its hemolytic activity towards human erythrocytes were also examined.

Results

In the predicted IP structure, the structure with an S-S bond was more stable than that without an S-S bond. The MIC after 24 h of incubation with IP was 0.156–1.25 μg/mL for MSSA and 0.625–2.5 μg/mL for MRSA. Compared with the mammalian antimicrobial peptide and other tick peptides, IP was highly effective against MRSA. Moreover, IP showed a dose-dependent bactericidal effect on both MSSA and MRSA after 1 h of incubation. IP had no observable effect on mammalian cell growth or morphology, on each cell DNA and on human erythrocytes.

Conclusions

We predicted the three-dimensional structure of IP and found that the structural integrity was maintained by three S-S bonds, which were energetically important for the stability and for forming α helix and β sheet. IP has cationic and amphipathic properties, which might be related to its antimicrobial activity. Furthermore, the antimicrobial activity of IP against MRSA was stronger than that of other antimicrobial peptides without apparent damage to mammalian and human cells, demonstrating its possible application as a new anti-MRSA medicine.

Antiplasmodial Activity Is an Ancient and Conserved Feature of Tick Defensins

Ancestral sequence reconstruction has been widely used to test evolution-based hypotheses. The genome of the European tick vector, Ixodes ricinus, encodes for defensin peptides with diverse antimicrobial activities against distantly related pathogens. These pathogens include fungi, Gram-negative, and Gram-positive bacteria, i.e., a wide antimicrobial spectrum. Ticks do not transmit these pathogens, suggesting that these defensins may act against a wide range of microbes encountered by ticks during blood feeding or off-host periods. As demonstrated here, these I. ricinus defensins are also effective against the apicomplexan parasite Plasmodium falciparum. To study the general evolution of antimicrobial activity in tick defensins, the ancestral amino acid sequence of chelicerate defensins, which existed approximately 444 million years ago, was reconstructed using publicly available scorpion and tick defensin sequences (named Scorpions-Ticks Defensins Ancestor, STiDA). The activity of STiDA was tested against P. falciparum and the same Gram-negative and Gram-positive bacteria that were used for the I. ricinus defensins. While some extant tick defensins exhibit a wide antimicrobial spectrum, the ancestral defensin showed moderate activity against one of the tested microbes, P. falciparum. This study suggests that amino acid variability and defensin family expansion increased the antimicrobial spectrum of ancestral tick defensins.

Tribolium castaneum defensins are primarily active against Gram-positive bacteria

The red flour beetle Tribolium castaneum is a destructive insect pest of stored food and feed products, and a model organism for development, evolutionary biology and immunity. The insect innate immune system includes antimicrobial peptides (AMPs) with a wide spectrum of targets including viruses, bacteria, fungi and parasites. Defensins are an evolutionarily-conserved class of AMPs and a potential new source of antimicrobial agents. In this context, we report the antimicrobial activity, phylogenetic and structural properties of three T. castaneum defensins (Def1, Def2 and Def3) and their relevance in the immunity of T. castaneum against bacterial pathogens. All three recombinant defensins showed bactericidal activity against Micrococcus luteus and Bacillus thuringiensis serovar tolworthi, but only Def1 and Def2 showed a bacteriostatic effect against Staphylococcus epidermidis. None of the defensins showed activity against the Gram-negative bacteria Escherichia coli and Pseudomonas entomophila or against the yeast Saccharomyces cerevisiae. All three defensins were transcriptionally upregulated following a bacterial challenge, suggesting a key role in the immunity of T. castaneum against bacterial pathogens. Phylogenetic analysis showed that defensins from T. castaneum, mealworms, Udo longhorn beetle and houseflies cluster within a well-defined clade of insect defensins. We conclude that T. castaneum defensins are primarily active against Gram-positive bacteria and that other AMPs may play a more prominent role against Gram-negative species.

Functional analysis of a novel cysteine-rich antimicrobial peptide from the salivary glands of the tick Rhipicephalus haemaphysaloides

Ticks encounter various microbes while sucking blood from an infected host and carrying these pathogens in themselves. Ticks can then transmit these pathogens to vertebrate hosts. The immune system of ticks can be stimulated to produce many bioactive molecules during feeding and pathogen invasion. Antimicrobial peptides (AMPs) are key effector molecules of a tick's immune response, as they can kill invading pathogenic microorganisms. In this study, we identified a novel cysteine-rich AMP, designated Rhamp1, in the salivary glands of unfed and fed female ticks (Rhipicephalus haemaphysaloides). Rhamp1 is encoded by a gene with an open reading frame of 333 bp, which in turn encodes a peptide of 12 kDa with a 22 amino acid residue signal peptide. The Rhamp1 protein had a pI of 8.6 and contained six conserved cysteine residues at the C-terminus. Rhamp1 shared 43% amino acid identity with a secreted cysteine-rich protein of another tick species, Ixodes scapularis. We cloned the Rhamp1 gene and attempted to express a recombinant protein using prokaryotic and eukaryotic systems, to determine its biological significance. Recombinant Rhamp1 was successfully expressed in both systems, yielding a glutathione S-transferase (GST)-tagged protein (36 kDa) from the prokaryotic system, and a polyhistidine-tagged Rhamp1 protein (14 kDa) from the eukaryotic system. Rhamp1 inhibited the activities of chymotrypsin (16%) and elastase (22%) and exerted low hemolytic activity. It also inhibited the growth of Gram-negative bacteria, including Pseudomonas aeruginosa (49%), Salmonella typhimurium (50%), and Escherichia coli (52%). Our findings suggest that Rhamp1 is a novel AMP in R. haemaphysaloides with the ability to inhibit proteinase activity.

Molecular characterization of a defensin gene from a hard tick, Dermacentor silvarum

Background

Ticks are distributed worldwide and considered as vectors of many human diseases. Tick defensins, a family of antimicrobial peptides, form the first line of defense against pathogens.

Findings

A defensin-like gene, named Ds-defensin, was identified from a cDNA library of the hard tick Dermacentor silvarum collected from northeast China. The full-length cDNA of Ds-defensin was 225 bp, encoding a 74 amino acid peptide. The nucleotide sequence of Ds-defensin shared 98.2% similarity to putative defensin from Dermacentor marginatus. RT-PCR results suggested that Ds-defensin was extensively expressed in tick salivary gland and midgut, with a higher expression level in midgut. Ds-defensin showed broad antimicrobial activity against various Gram-positive and Gram-negative bacteria, as well as the fungus Candida albicans.

Conclusions

We characterized a functional defensin from D. silvarum of China. Ds-defensin showed bactericidal activity against various Gram-positive and Gram-negative bacteria. Ds-defensin can be expected to be introduced to the medical field as a new molecule with antibacterial activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0625-0) contains supplementary material, which is available to authorized users.

Defensin from the ornate sheep tick Dermacentor marginatus and its effect on Lyme borreliosis spirochetes

Expression of the previously reported defensin of the tick Dermacentor marginatus (defDM) was analysed in different organs by RT-PCR. mRNA of the defDM gene was detected in the hemolymph, midgut and salivary glands. Moreover defDM was isolated from the tick hemolymph using RP-HPLC and its sequence was determined by mass spectrometry and Edman degradation. Synthetic peptide was used for determining biological activities. The results showed an anti-Gram-positive bacterial role for the defensin. As D. marginatus ticks appear not to be vectors of the Lyme disease agent of the complex Borrelia burgdorferi sensu lato, we tested the influence of defDM on Borrelia afzelii. There is a very clear borrelicidal activity of the defensin, which is concentration dependent and suggests a possible role in the clearing of Borrelia ingested by D. marginatus ticks.

Identification and partial characterisation of new members of the Ixodes ricinus defensin family

The hard-bodied tick Ixodes ricinus (castor bean tick) is the most common tick species in Europe. I. ricinus is a vector of the causative agents of diseases that affect humans and animals including tick-borne encephalitis, borreliosis, tick-borne fever and babesiosis. The innate immune system provides ticks with quite an efficient defence against some pathogenic microorganisms in the event of their penetration into the tick body or through the blood meal. Antimicrobial peptides (AMPs) constitute an important feature of the tick immune system. Defensins are a well-known class of AMPs. Members of the defensin family of proteins have been reported in several tick species. So far, only two defensins had been identified from I. ricinus. In this study, we report the identification of six novel putative defensins from I. ricinus at the genomic and transcriptional levels. At the genomic level they show differences with one being intronless, while others contain two introns. The expression pattern of these molecules in the salivary glands, midgut, ovary, Malpighian tubules, haemolymph and the tick cell line IRE/CTVM19 was determined. Some of them are tissue specific while others seem to be ubiquitous. Molecular and phylogenetic analyses show that these novel members of the I. ricinus defensin family differ phylogenetically and structurally; nevertheless, the cysteine pattern is highly conserved among the family members. Finally, antimicrobial-peptide prediction tools were used to predict putative antimicrobial activity of our defensins. They show putative antimicrobial activity mainly against Gram-positive bacteria. This study displays the diversity of the defensin family in the tick I. ricinus.

Functional characterization of two defensin isoforms of the hard tick Ixodes ricinus

BACKGROUND

The immune system of ticks is stimulated to produce many pharmacologically active molecules during feeding and especially during pathogen invasion. The family of cationic peptides - defensins - represents a specific group of antimicrobial compounds with six conserved cysteine residues in a molecule.

RESULTS

Two isoforms of the defensin gene (def1 and def2) were identified in the European tick Ixodes ricinus. Expression of both genes was induced in different tick organs by a blood feeding or pathogen injection. We have tested the ability of synthetic peptides def1 and def2 to inhibit the growth or directly kill several pathogens. The antimicrobial activities (expressed as minimal inhibition concentration and minimal bactericidal concentration values) against Gram positive bacteria were confirmed, while Gram negative bacteria, yeast, Tick Borne Encephalitis and West Nile Viruses were shown to be insensitive. In addition to antimicrobial activities, the hemolysis effect of def1 and def2 on human erythrocytes was also established.

CONCLUSIONS

Although there is nothing known about the realistic concentration of defensins in I. ricinus tick body, these results suggest that defensins play an important role in defence against different pathogens. Moreover this is a first report of a one amino acid substitution in a defensins molecule and its impact on antimicrobial activity.

Tertiary structure-related activity of tick defensin (persulcatusin) in the taiga tick, Ixodes persulcatus

Defensins are small cysteine-rich cationic proteins found in both vertebrates and invertebrates constituting the front line of host innate immunity. To examine the importance of the tertiary structure of tick defensin in its antimicrobial activity, we synthesized two types of the peptides with tertiary structure or primary one on basis of the information of the sequence in the defensin originated from the taiga tick, Ixodes persulcatus. Chemically synthesized peptides were used to investigate the activity spectrum against Staphylococcus aureus, Borrelia garinii and flora-associated bacteria. Both synthetic peptides showed antimicrobial activity against S. aureus in short-time killing within 1 h, but they do not show the activity against B. garinii, Stenotrophomonas maltophila and Bacillus spp., which were frequently isolated from the midgut of I. persulcatus. The teriary structure brought more potent activity to S. aureus than primary one in short-time killing. We also examined its antimicrobial activity by evaluation of growth inhibition in the presence of the synthetic peptides. Minimum inhibitory concentration (MIC) was ranged from 1.2 to 5.0 μg/ml in tertiary peptide and from 10 to 40 μg/ml in primary peptide, when 10 strains of S. aureus were used. From the curve of cumulative inhibition rates, MIC50 (MIC which half of the strains showed) to S. aureus is about 1.2 μg/ml in the peptide with tertiary structure and about 10 μg/ml in the linear one. Corynebacterium renale is 10 times or more sensitive to tertiary peptide than primary one. In conclusion, the presence of 3 disulfide bridges, which stabilize the molecule and maintain the tertiary structure, is considered to have an effect on their antimicrobial activities against Gram-positive bacteria such as S. aureus.

Borrelia burgdorferi resistance to a major skin antimicrobial peptide is independent of outer surface lipoprotein content

We hypothesize a potential role for Borrelia burgdorferi OspC in innate immune evasion at the initial stage of mammalian infection. We demonstrate that B. burgdorferi is resistant to high levels (>200 microg/ml) of cathelicidin and that this antimicrobial peptide exhibits limited binding to the spirochetal outer membrane, irrespective of OspC or other abundant surface lipoproteins. We conclude that the essential role of OspC is unrelated to resistance to this component of innate immunity.