Activity of novel inhibitors of <Emphasis Type="Italic">Staphylococcus aureus</Emphasis> biofilms

Staphylococcus aureus is one of the most important pathogens causing chronic biofilm infections. These are becoming more difficult to treat owing to drug resistance, particularly because S. aureus biofilms limit the efficacy of antimicrobial agents, leading to high morbidity and mortality. In the present study, we screened for inhibitors of S. aureus biofilm formation using a natural product library from the Korea Chemical Bank (KCB). Screening by crystal violet-based biomass staining assay identified hit compounds. Further examination of antibiofilm properties of these compounds was conducted and led to the identification of celastrol and telithromycin. In vitro, both celastrol and telithromycin were toxic to planktonic S. aureus and also active against a clinical methicillin-resistant S. aureus (MRSA) isolate. The effect of the compounds on preformed biofilms of clinical MRSA isolates was evaluated by confocal laser scanning microscopy (CLSM), which revealed the absence of typical biofilm architecture. In addition, celastrol and telithromycin inhibited the production of extracellular protein at selected sub-MIC concentrations, which revealed the reduced extracellular polymeric substance (EPS) secretion. Celastrol exhibited greater cytotoxicity than telithromycin. These data suggest that the hit compounds, especially telithromycin, could be considered novel inhibitors of S. aureus biofilm. Although the mechanisms of the effects on S. aureus biofilms are not fully understood, our data suggest that telithromycin could be a useful adjuvant therapeutic agent for S. aureus biofilm-related infections.     

Effective Removal of Staphylococcal Biofilms by the Endolysin LysH5

Staphylococcal biofilms are a major concern in both clinical and food settings because they are an important source of contamination. The efficacy of established cleaning procedures is often hindered due to the ability of some antimicrobial compounds to induce biofilm formation, and to the presence of persister cells, a small bacterial subpopulation that exhibits multidrug tolerance. Phage lytic enzymes have demonstrated antimicrobial activity against planktonic and sessile bacteria. However, their ability to lyse and/or select persister cells remains largely unexplored so far. In this work, the lytic activity of the endolysin LysH5 against Staphylococcus aureus and Staphylococcus epidermidis biofilms was confirmed. LysH5 reduced staphylococcal sessile cell counts by 1–3 log units, compared with the untreated control, and sub-inhibitory concentrations of this protein did not induce biofilm formation. LysH5-surviving cells were not resistant to the lytic activity of this protein, suggesting that no persister cells were selected. Moreover, to prove the lytic ability of LysH5 against this subpopulation, both S. aureus exponential cultures and persister cells obtained after treatment with rifampicin and ciprofloxacin were subsequently treated with LysH5. The results demonstrated that besides the notable activity of endolysin LysH5 against staphylococcal biofilms, persister cells were also inhibited, which raises new opportunities as an adjuvant for some antibiotics.     

The Antibacterial Properties of 4, 8, 4′, 8′-Tetramethoxy (1,1′-biphenanthrene) -2,7,2′,7′-Tetrol from Fibrous Roots of Bletilla striata

Biphenanthrene compound, 4, 8, 4′, 8′-tetramethoxy (1, 1′-biphenanthrene)—2, 7, 2′, 7′-tetrol (LF05), recently isolated from fibrous roots of Bletilla striata, exhibits antibacterial activity against several Gram-positive bacteria. In this study, we investigated the antibacterial properties, potential mode of action and cytotoxicity. Minimum inhibitory concentrations (MICs) tests showed LF05 was active against all tested Gram-positive strains, including methicillin-resistant Staphylococcus aureus (MRSA) and staphylococcal clinical isolates. Minimum bactericidal concentration (MBC) tests demonstrated LF05 was bactericidal against S. aureus ATCC 29213 and Bacillus subtilis 168 whereas bacteriostatic against S. aureus ATCC 43300, WX 0002, and other strains of S. aureus. Time-kill assays further confirmed these observations. The flow cytometric assay indicated that LF05 damaged the cell membrane of S. aureus ATCC 29213 and B. subtilis 168. Consistent with this finding, 4 × MIC of LF05 caused release of ATP in B. subtilis 168 within 10 min. Checkerboard test demonstrated LF05 exhibited additive effect when combined with vancomycin, erythromycin and berberine. The addition of rat plasma or bovine serum albumin to bacterial cultures caused significantly loss in antibacterial activity of LF05. Interestingly, LF05 was highly toxic to several tumor cells. Results of these studies indicate that LF05 is bactericidal against some Gram-positive bacteria and acts as a membrane structure disruptor. The application of biphenanthrene in the treatment of S. aureus infection, especially local infection, deserves further study.     

Toward an Alternative Therapeutic Approach for Skin Infections: Antagonistic Activity of Lactobacilli Against Antibiotic-Resistant Staphylococcus aureus and Pseudomonas aeruginosa

The wide spread of antimicrobial resistance has urged the need of alternative therapeutic approach. In this context, probiotic lactobacilli have been reported for the prevention and treatment of many gastrointestinal and urogenital infections. However, very little is known about their antagonistic activity against skin pathogens. Accordingly, the present study aimed to investigate the potential of lactobacilli to interfere with pathogenesis features of two antibiotic-resistant skin pathogens, namely methicillin-resistant Staphylococcus aureus and multiple-resistant Pseudomonas aeruginosa. A total of 49 lactobacilli were recovered, identified and tested for their antagonistic activities against the aforementioned pathogens. Of these, eight isolates were capable of blocking the adherence of pathogens to mammalian cells independent of the skin pathogen tested or model adopted. Moreover, three Lactobacillus isolates (LRA4, LC2 and LR5) effectively prevented the pathogen internalization into epithelial cells in addition to potentiating phagocyte-mediated pathogen killing. Interestingly, the lactobacilli LC2, LF9 and LRA4 markedly inhibited the growth of P. aeruginosa and S. aureus isolates in coculture experiments. Besides, the lactobacilli LRA4, LC2, LR5 and LF9 have counteracted pathogen cytotoxicity. Taken together, the present study revealed some inhibitory activities of lactobacilli against two antibiotic-resistant skin pathogens. Moreover, it revealed two lactobacilli, namely LC2 and LRA4, with antagonistic capacity against different virulence determinants of skin pathogens. These lactobacilli are considered promising probiotic candidates that may represent an alternative therapeutic approach for skin infections.     

The novel antimicrobial peptide PXL150 in the local treatment of skin and soft tissue infections

Dramatic increase in bacterial resistance towards conventional antibiotics emphasises the importance to identify novel, more potent antimicrobial therapies. Antimicrobial peptides (AMPs) have emerged as a promising new group to be evaluated in therapeutic intervention of infectious diseases. Here we describe a novel AMP, PXL150, which demonstrates in vitro a broad spectrum microbicidal action against both Gram-positive and Gram-negative bacteria, including resistant strains. The potent microbicidal activity and broad antibacterial spectrum of PXL150 were not associated with any hemolytic activity. Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) failed to develop resistance towards PXL150 during continued selection pressure. PXL150 caused a rapid depolarisation of cytoplasmic membrane of S. aureus, and dissipating membrane potential is likely one mechanism for PXL150 to kill its target bacteria. Studies in human cell lines indicated that PXL150 has anti-inflammatory properties, which might be of additional benefit. PXL150 demonstrated pronounced anti-infectious effect in an in vivo model of full thickness wounds infected with MRSA in rats and in an ex vivo model of pig skin infected with S. aureus. Subcutaneous or topical application of the peptide in rats did not lead to any adverse reactions. In conclusion, PXL150 may constitute a new therapeutic alternative for local treatment of infections, and further studies are warranted to evaluate the applicability of this AMP in clinical settings.     

Anti-infective efficacy of the lactoferrin-derived antimicrobial peptide HLR1r

Antimicrobial peptides (AMPs) have emerged as a new class of drug candidates for the treatment of infectious diseases. Here we describe a novel AMP, HLR1r, which is structurally derived from the human milk protein lactoferrin and demonstrates a broad spectrum microbicidal action in vitro. The minimum concentration of HLR1r needed for killing ≥99% of microorganisms in vitro, was in the range of 3–50 μg/ml for common Gram-negative and Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), and for the yeast Candida albicans, when assessed in diluted brain-heart infusion medium. We found that HLR1r also possesses anti-inflammatory properties as evidenced by inhibition of tumor necrosis factor alpha (TNF-α) secretion from human monocyte-derived macrophages and by repression of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1) secretion from human mesothelial cells, without any cytotoxic effect observed at the concentration range tested (up to 400 μg/ml). HLR1r demonstrated pronounced anti-infectious effect in in vivo experimental models of cutaneous candidiasis in mice and of excision wounds infected with MRSA in rats as well as in an ex vivo model of pig skin infected with S. aureus. In conclusion, HLR1r may constitute a new therapeutic alternative for local treatment of skin infections.     

Limnonectins: a new class of antimicrobial peptides from the skin secretion of the Fujian large-headed frog (Limnonectes fujianensis)

Amphibian skin secretions are rich sources of biologically-active peptides with antimicrobial peptides predominating in many species. Several studies involving molecular cloning of biosynthetic precursor-encoding cDNAs from skin or skin secretions have revealed that these exhibit highly-conserved domain architectures with an unusually high degree of conserved nucleotide and resultant amino acid sequences within the signal peptides. This high degree of nucleotide sequence conservation has permitted the design of primers complementary to such sites facilitating “shotgun” cloning of skin or skin secretion-derived cDNA libraries from hitherto unstudied species. Here we have used such an approach using a skin secretion-derived cDNA library from an unstudied species of Chinese frog - the Fujian large-headed frog, Limnonectes fujianensis - and have discovered two 16-mer peptides of novel primary structures, named limnonectin-1Fa (SFPFFPPGICKRLKRC) and limnonectin-1Fb (SFHVFPPWMCKSLKKC), that represent the prototypes of a new class of amphibian skin antimicrobial peptide. Unusually these limnonectins display activity only against a Gram-negative bacterium (MICs of 35 and 70 μM) and are devoid of haemolytic activity at concentrations up to 160 μM. Thus the “shotgun” cloning approach described can exploit the unusually high degree of nucleotide conservation in signal peptide-encoding domains of amphibian defensive skin secretion peptide precursor-encoding cDNAs to rapidly expedite the discovery of novel and functional defensive peptides in a manner that circumvents specimen sacrifice without compromising robustness of data.     

In vitro efficacy of bismuth thiols against biofilms formed by bacteria isolated from human chronic wounds

Aims: The purpose of this study was to evaluate the antimicrobial efficacy of thirteen bismuth thiol preparations for bactericidal activity against established biofilms formed by two bacteria isolated from human chronic wounds. Methods: Single species biofilms of a Pseudomonas aeruginosa or a methicillin‐resistant Staphylococcus aureus were grown in either colony biofilm or drip‐flow reactors systems. Biofilms were challenged with bismuth thiols, antibiotics or silver sulfadiazine, and log reductions were determined by plating for colony formation. Conclusions: Antibiotics were ineffective or inconsistent against biofilms of both bacterial species tested. None of the antibiotics tested were able to achieve >2 log reductions in both biofilm models. The 13 different bismuth thiols tested in this investigation achieved widely varying degrees of killing, even against the same micro‐organism in the same biofilm model. For each micro‐organism, the best bismuth thiol easily outperformed the best conventional antibiotic. Against P. aeruginosa biofilms, bismuth‐2,3‐dimercaptopropanol (BisBAL) at 40–80 μg ml^?1 achieved >7·7 mean log reduction for the two biofilm models. Against MRSA biofilms, bismuth‐1,3‐propanedithiol/bismuth‐2‐mercaptopyridine N‐oxide (BisBDT/PYR) achieved a 4·9 log reduction. Significance and Impact of the Study: Bismuth thiols are effective antimicrobial agents against biofilms formed by wound bacteria and merit further development as topical antiseptics for the suppression of biofilms in chronic wounds.     

Surface disinfection properties of the combination of an antimicrobial peptide,ranalexin, with an endopeptidase,lysostaphin, against methicillin‐resistant Staphylococcus aureus (MRSA)

Aims: To characterize the antibacterial synergy of the antimicrobial peptide, ranalexin, used in combination with the anti‐staphylococcal endopeptidase, lysostaphin, against methicillin‐resistant Staphylococcus aureus (MRSA), and to assess the combination’s potential as a topical disinfectant or decolonizing agent for MRSA. MRSA causes potentially lethal infections, and pre‐operative patients colonized with MRSA are often treated with chlorhexidine digluconate and mupirocin cream to eradicate carriage. However, chlorhexidine is unsuitable for some patients, and mupirocin resistance is increasingly encountered, indicating new agents are required. Methods and Results: Using an ex vivo assay, ranalexin and lysostaphin tested in combination reduced viable MRSA on human skin to a greater extent than either compound individually. The combination killed bacteria within 5 min and remained effective and synergistic even in high salt and low pH conditions. Conclusions: The combination is active against MRSA on human skin and under conditions that may be encountered in sweat. Significance and Impact of the Study: Although the exact mechanism of activity remains unresolved, considering its specific spectrum of activity, fast killing kinetics and low likelihood of resistance arising, the combination of ranalexin with lysostaphin warrants consideration as a new agent to eradicate nasal and skin carriage of Staph. aureus, including MRSA.     

Novel families of antimicrobial peptides with multiple functions from skin of Xizang plateau frog, Nanorana parkeri

Xizang plateau frog (Nanorana parkeri) captured in Lhasa, Tibet, China, solely lives in the subtropical plateau, where there is strong ultraviolet radiation and long duration of sunshine. Considering its harsh living environment, the frog's innate defense against microbes and environmental stress was investigated. In current study, three antimicrobial peptides (AMPs) were purified and characterized from the skin secretion of N. parkeri. The coding cDNA sequences were also cloned from the skin cDNA library of N. parkeri. By structural characterization, two peptides were identified belonging to Japonicin-1 family, and named as Japonicin-1Npa (FLLFPLMCKIQGKC) and Japonicin-1Npb (FVLPLVMCKILRKC). The third peptide isolated named Parkerin with a unique sequence of GWANTLKNVAGGLCKITGAA did not show similarity to any known amphibian AMPs. Multi-functions of three AMPs were examined (antioxidant, MCD, hemolytic etc). Their solution structures determined by CD and antimicrobial mechanisms investigated by SEM are very well consistent with their functional characters. Current result suggests that these novel multi-functional AMPs could play an important role in defending N. parkeri against environmental oxidative stress and pathogenic microorganisms, which may partially reveal the ecological adaptation of these plateau-living amphibians.     

Hylaranins: prototypes of a new class of amphibian antimicrobial peptide from the skin secretion of the oriental broad-folded frog,Hylarana latouchii

Amphibian skin secretions contain a broad spectrum of biologically active compounds, particularly antimicrobial peptides, which are considered to constitute a first line of defence against bacterial infection. Here we describe the identification of two prototype peptides representing a novel structural class of antimicrobial peptide from the skin secretion of the oriental broad-folded frog, Hylarana latouchii. Named hylaranin-L1 (GVLSAFKNALPGIMKIIVamide) and hylaranin-L2 (GVLSVIKNALPGIMRFIAamide), both peptides consist of 18 amino acid residues, are C-terminally amidated and are of unique primary structures. Their primary structures were initially deduced by MS/MS fragmentation sequencing from reverse-phase HPLC fractions of skin secretion that demonstrated antimicrobial activity. Subsequently, their precursor-encoding cDNAs were cloned from a skin secretion-derived cDNA library and their primary structures were confirmed unequivocally. Synthetic replicates of both peptides exhibited broad-spectrum antimicrobial activity with mean inhibitory concentrations (MICs) of 34 μM against Gram-negative Escherichia coli, 4.3 μM against Gram-positive Staphylococcus aureus and 4–9 μM against the yeast, Candida albicans. Both peptides exhibited little haemolytic activity (<6 %) at the MICs for S. aureus and C. albicans. Amphibian skin secretions thus continue to provide novel antimicrobial peptide structures that may prove to be lead compounds in the design of new classes of anti-infection therapeutics.     

In vitro activity of vancomycin, quinupristin/dalfopristin, and linezolid against intact and disrupted biofilms of staphylococci

 

Shed cells or disrupted parts of the biofilm may enter the circulation causing serious and very hard to treat biofilm-associated infections. The activity of antimicrobial agents against the shed cells/disrupted biofilms is largely unknown.

Methods

We studied the in vitro susceptibility of intact and disrupted biofilms of thirty clinical isolates of methicillin-resistant and methicillin–susceptible Staphylococcus aureus (MRSA and MSSA) and Staphylococcus epidermidis to vancomycin, quinupristin/dalfopristin, and linezolid and compared it to that of the suspended (planktonic) cells.

Results

Bacteria in the disrupted biofilms were as resistant as those in the intact biofilms at the minimum inhibitory concentrations of the antibiotics. At higher concentrations, bacteria in the disrupted biofilms were significantly (P < 0.001) less resistant than those in the intact biofilms but more resistant than the planktonic cells. Quinupristin/dalfopristin showed the best activity against cells of the disrupted biofilms at concentrations above MICs and vancomycin, at 500 and 1,000 μg/ml, was significantly more active against the biofilms of MRSA and S. epidermidis

Conclusion

The difficulty of treating biofilm-associated infections may be attributed not only to the difficulty of eradicating the biofilm focus but also to the lack of susceptibility of cells disrupted from the biofilm to antimicrobial agents.     

Lipoic acid modified antimicrobial peptide with enhanced antimicrobial properties

RIWVIWRR-NH₂ (Bac8c) is a natural antimicrobial peptide (AMP) exhibiting great antibacterial activity against Gram-negative and Gram-positive bacteria. In this work, lipoic acid was used as a fatty acid hydrophobic ligand to modify Bac8c (LA-Bac8c) to further improve its antimicrobial properties. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) assays showed that LA-Bac8c exhibited lower MIC (MBC) values against Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) than Bac8c. Similar results were reflected in the antibiofilm activity towards S. aureus and MRSA, and LA-Bac8c showed better activity to the biofilm which has been formed or is being formed. In addition to this, the obvious interaction between bacteria/biofilm and LA-Bac8c was observed by microscopy. LA-Bac8c displayed strong membrane depolarization and outer membrane permeabilizing ability, and the cell membrane treated with LA-Bac8c was destroyed to the leakage of bacteria cellular components. All these data indicated LA-Bac8c could be used as a useful antimicrobial peptide with wide application prospect.     

Roemerine Improves the Survival Rate of Septicemic BALB/c Mice by Increasing the Cell Membrane Permeability of Staphylococcus aureus

Staphylococcus aureus is one of the most frequently occurring hospital- and community-associated pathogenic bacteria featuring high morbidity and mortality. The occurrence of methicillin-resistant S. aureus (MRSA) has increased persistently over the years. Therefore, developing novel anti-MRSA drugs to circumvent drug resistance of S. aureus is highly important. Roemerine, an aporphine alkaloid, has previously been reported to exhibit antibacterial activity. The present study aimed to investigate whether roemerine can maintain these activities against S.aureus in vivo and further explore the underlying mechanism. We found that roemerine is effective in vitro against four S. aureus strains as well as in vivo against MRSA insepticemic BALB/c mice. Furthermore, roemerine was found to increase cell membrane permeability in a concentration-dependent manner. These findings suggest that roemerine may be developed as a promising compound for treating S. aureus, especially methicillin-resistant strains of these bacteria.     

Antibacterial Activity of THAM Trisphenylguanide against Methicillin-Resistant Staphylococcus aureus

This study investigated the potential antibacterial activity of three series of compounds synthesized from 12 linear and branched polyamines with 2–8 amino groups, which were substituted to produce the corresponding guanides, biguanides, or phenylguanides, against Acinetobacter baumannii, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. Antibacterial activity was measured for each compound by determining the minimum inhibitory concentration against the bacteria, and the toxicity towards mammalian cells was determined. The most effective compound, THAM trisphenylguanide, was studied in time-to-kill and cytoplasmic leakage assays against methicillin-resistant Staphylococcus aureus (MRSA, USA300) in comparison to chlorhexidine. Preliminary toxicity and MRSA challenge studies in mice were also conducted on this compound. THAM trisphenylguanide showed significant antibacterial activity (MIC ∼1 mg/L) and selectivity against MRSA relative to all the other bacteria examined. In time-to-kill assays it showed increased antimicrobial activity against MRSA versus chlorhexidine. It induced leakage of cytoplasmic content at concentrations that did not reduce cell viability, suggesting the mechanism of action may involve membrane disruption. Using an intraperitoneal mouse model of invasive MRSA disease, THAM trisphenylguanide reduced bacterial burden locally and in deeper tissues. This study has identified a novel guanide compound with selective microbicidal activity against Staphylococcus aureus, including a methicillin-resistant (MRSA) strain.     

Evaluation of antimicrobial activity of bacterial symbionts isolated from wild field cockroach Blattella vaga from Saudi Arabia

Drug-resistant pathogens form the main threat to global health during the current century. Annually, a lot of patients die in hospitals due to infection with one or more drug-resistant bacteria especially Staphylococcus aureus (MRSA). In the absence of new effective antimicrobial drugs, the number of deaths said to be increased. Searching for new antibiotics in our backyard form a part of scientist strategies to solve such serious health problem. Insects consider one of such interesting sources of the new era of antimicrobial drugs. Cockroaches as an example can live and adapt in a polluted area for a long time, so through this work field cockroach, Blattella vaga was collected from two semi-wild areas around Riyadh, Saudi Arabia for isolation of gut bacteria searching for new antimicrobial agents. Three species of bacteria were identified from field cockroach gut: Bacillus licheniformis, Bacillus subtilis, and Kocuria rosea. The three species were isolated, purified, and tested for their antimicrobial activity against four drug-resistant pathogens (three bacteria: Salmonella enterica (ATCC25566), Staphylococcus aureus (MRSA) (Clinical strain), and Streptococcus mutans (RCMB 017(1) ATCC ® 25175™) and one fungus: Candida albicans (RCMB005003(1) ATCC® 10231™)). The results show no antimicrobial activity of Bacillus subtilis and very good activity Bacillus licheniformis and Kocuria rosea. Bacillus licheniformis gives very effective activity against Candida albicans while Kocuria rosea is effective against MRSA and Streptococcus mutans. None of the gut isolated bacteria show any activity against Salmonella enterica. Such results revealed that the metabolites of these bacteria could be used as substitutes to the already used antibiotics to overcome the problem of multidrug-resistant human pathogens.     

Synergism between Medihoney and Rifampicin against Methicillin-Resistant Staphylococcus aureus (MRSA)

Skin and chronic wound infections caused by highly antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) are an increasing and urgent health problem worldwide, particularly with sharp increases in obesity and diabetes. New Zealand manuka honey has potent broad-spectrum antimicrobial activity, has been shown to inhibit the growth of MRSA strains, and bacteria resistant to this honey have not been obtainable in the laboratory. Combinational treatment of chronic wounds with manuka honey and common antibiotics may offer a wide range of advantages including synergistic enhancement of the antibacterial activity, reduction of the effective dose of the antibiotic, and reduction of the risk of antibiotic resistance. The aim of this study was to investigate the effect of Medihoney in combination with the widely used antibiotic rifampicin on S. aureus. Using checkerboard microdilution assays, time-kill curve experiments and agar diffusion assays, we show a synergism between Medihoney and rifampicin against MRSA and clinical isolates of S. aureus. Furthermore, the Medihoney/rifampicin combination stopped the appearance of rifampicin-resistant S. aureus in vitro. Methylglyoxal (MGO), believed to be the major antibacterial compound in manuka honey, did not act synergistically with rifampicin and is therefore not the sole factor responsible for the synergistic effect of manuka honey with rifampicin. Our findings support the idea that a combination of honey and antibiotics may be an effective new antimicrobial therapy for chronic wound infections.     

A frog-derived antimicrobial peptide as a potential anti-biofilm agent in combating Staphylococcus aureus skin infection

Staphylococcus aureus (S. aureus), one of the most prevalent bacteria found in atopic dermatitis lesions, can induce ongoing infections and inflammation by downregulating the expression of host defence peptides in the skin. In addition, the emergence of the ‘superbug’ Methicillin-resistant S. aureus (MRSA) has made the treatment of these infections more challenging. Antimicrobial peptides (AMPs), due to their potent antimicrobial activity, limited evidence of resistance development, and potential immunomodulatory effects, have gained increasing attention as potential therapeutic agents for atopic dermatitis. In this study, we report a novel AMP, brevinin-1E-OG9, isolated from the skin secretions of Odorrana grahami, which shows potent antibacterial activity, especially against S. aureus. Based on the characteristics of the ‘Rana Box’, we designed a set of brevinin-1E-OG9 analogues to explore its structure–activity relationship. Brevinin-1E-OG9c-De-NH₂ exhibited the most potent antimicrobial efficacy in both in vitro and ex vivo studies and attenuated inflammatory responses induced by lipoteichoic acid and heat-killed microbes. As a result, brevinin-1E-OG9c-De-NH₂ might represent a promising candidate for the treatment of S. aureus skin infections.     

Combination of Silver Nanoparticles and Drosera binata Extract as a Possible Alternative for Antibiotic Treatment of Burn Wound Infections Caused by Resistant Staphylococcus aureus

Staphylococcus aureus is the most common infectious agent involved in the development of skin infections that are associated with antibiotic resistance, such as burn wounds. As drug resistance is a growing problem it is essential to establish novel antimicrobials. Currently, antibiotic resistance in bacteria is successfully controlled by multi-drug therapies. Here we demonstrate that secondary metabolites present in the extract obtained from Drosera binata in vitro cultures are effective antibacterial agents against S. aureus grown in planktonic culture and in biofilm. Moreover, this is the first report demonstrating the synergistic interaction between the D. binata extract and silver nanoparticles (AgNPs), which results in the spectacular enhancement of the observed bactericidal activity, while having no cytotoxic effects on human keratinocytes. Simultaneous use of these two agents in significantly reduced quantities produces the same effect, i.e. by killing 99.9% of bacteria in inoculum or eradicating the staphylococcal biofilm, as higher amounts of the agents used individually. Our data indicates that combining AgNPs with either the D. binata extract or with its pure compound (3-chloroplumbagin) may provide a safe and highly effective alternative to commonly used antibiotics, which are ineffective towards the antibiotic-resistant S. aureus.