Short, Synthetic Cationic Peptides Have Antibacterial Activity against Mycobacterium smegmatis by Forming Pores in Membrane and Synergizing with Antibiotics

Development of a defibrinated human blood hemolysis assay for rapid testing of hemolytic activity compared to computational prediction

Cytotoxicity studies determining hemolytic properties of antimicrobial peptides or other drugs are an important step in the development of novel therapeutics for clinical use. Hemolysis is an affordable, accessible, and rapid method for initial assessment of cellular toxicity for all drugs under development. However, variability in species of red blood cells and protocols used may result in significant differences in results. AMPs generally possess higher selectivity for bacterial cells but can have toxicity against host cells at high concentrations. Knowing the hemolytic activity of the peptides we are developing contributes to our understanding of their potential toxicity. Computational approaches for predicting hemolytic activity of AMPs exist and were tested head-to-head with our experimental results.

RESULTS

Starting with an observation of high hemolytic activity of LL-37 peptide against human red blood cells that were collected in EDTA, we explored alternative approaches to develop a more robust, accurate and simple hemolysis assay using defibrinated human blood. We found significant differences between the sensitivity of defibrinated red blood cells and EDTA treated red blood cells.

SIGNIFICANCE

Accurately determining the hemolytic activity using human red blood cells will allow for a more robust calculation of the therapeutic index of our potential antimicrobial compounds, a critical measure in their pre-clinical development.

CONCLUSION

We introduce a standardized, more accurate protocol for assessing hemolytic activity using defibrinated human red blood cells. This approach, facilitated by the increased commercial availability of de-identified human blood and defibrination methods, offers a robust tool for evaluating toxicity of emerging drug compounds, especially AMPs.

Antimicrobial peptides as promising antibiotic adjuvants to combat drug-resistant pathogens

The widespread antimicrobial resistance (AMR) calls for the development of new antimicrobial strategies. Antibiotic adjuvant rescues antibiotic activity and increases the life span of the antibiotics, representing a more productive, timely, and cost-effective strategy in fighting drug-resistant pathogens. Antimicrobial peptides (AMPs) from synthetic and natural sources are considered new-generation antibacterial agents. Besides their direct antimicrobial activity, growing evidence shows that some AMPs effectively enhance the activity of conventional antibiotics. The combinations of AMPs and antibiotics display an improved therapeutic effect on antibiotic-resistant bacterial infections and minimize the emergence of resistance. In this review, we discuss the value of AMPs in the age of resistance, including modes of action, limiting evolutionary resistance, and their designing strategies. We summarise the recent advances in combining AMPs and antibiotics against antibiotic-resistant pathogens, as well as their synergistic mechanisms. Lastly, we highlight the challenges and opportunities associated with the use of AMPs as potential antibiotic adjuvants. This will shed new light on the deployment of synergistic combinations to address the AMR crisis.

GATR-3, a Peptide That Eradicates Preformed Biofilms of Multidrug-Resistant Acinetobacter baumannii

Acinetobacter baumannii is a gram-negative bacterium that causes hospital-acquired and opportunistic infections, resulting in pneumonia, sepsis, and severe wound infections that can be difficult to treat due to antimicrobial resistance and the formation of biofilms. There is an urgent need to develop novel antimicrobials to tackle the rapid increase in antimicrobial resistance, and antimicrobial peptides (AMPs) represent an additional class of potential agents with direct antimicrobial and/or host-defense activating activities. In this study, we present GATR-3, a synthetic, designed AMP that was modified from a cryptic peptide discovered in American alligator, as our lead peptide to target multidrug-resistant (MDR) A. baumannii. Antimicrobial susceptibility testing and antibiofilm assays were performed to assess GATR-3 against a panel of 8 MDR A. baumannii strains, including AB5075 and some clinical strains. The GATR-3 mechanism of action was determined to be via loss of membrane integrity as measured by DiSC3(5) and ethidium bromide assays. GATR-3 exhibited potent antimicrobial activity against all tested multidrug-resistant A. baumannii strains with rapid killing. Biofilms are difficult to treat and eradicate. Excitingly, GATR-3 inhibited biofilm formation and, more importantly, eradicated preformed biofilms of MDR A. baumannii AB5075, as evidenced by MBEC assays and scanning electron micrographs. GATR3 did not induce resistance in MDR A. baumannii, unlike colistin. Additionally, the toxicity of GATR-3 was evaluated using human red blood cells, HepG2 cells, and waxworms using hemolysis and MTT assays. GATR-3 demonstrated little to no cytotoxicity against HepG2 and red blood cells, even at 100 μg/mL. GATR-3 injection showed little toxicity in the waxworm model, resulting in a 90% survival rate. The therapeutic index of GATR-3 was estimated (based on the HC50/MIC against human RBCs) to be 1250. Overall, GATR-3 is a promising candidate to advance to preclinical testing to potentially treat MDR A. baumannii infections.

The antimicrobial peptide Esc(1-21)-1c increases susceptibility of Pseudomonas aeruginosa to conventional antibiotics by decreasing the expression of the MexAB-OprM efflux pump

Introduction: The increase in bacterial strains resistant to conventional antibiotics is an alarming problem for human health and could lead to pandemics in the future. Among bacterial pathogens responsible for a large variety of severe infections there is Pseudomonas aeruginosa. Therefore, there is an urgent need for new molecules with antimicrobial activity or that can act as adjuvants of antibiotics already in use. In this scenario, antimicrobial peptides (AMPs) hold great promise. Recently, we characterized a frog-skin AMP derived from esculentin-1a, namely Esc(1-21)-1c, endowed with antipseudomonal activity without being cytotoxic to human cells. Methods: The combinatorial effect of the peptide and antibiotics was investigated through the checkerboard assay, differential proteomic and transcriptional analysis. Results: Here, we found that Esc(1-21)-1c can synergistically inhibit the growth of P. aeruginosa cells with three different antibiotics, including tetracycline. We therefore investigated the underlying mechanism implemented by the peptide using a differential proteomic approach. The data revealed a significant decrease in the production of three proteins belonging to the MexAB-OprM efflux pump upon treatment with sub-inhibitory concentration of Esc(1-21)-1c. Down-regulation of these proteins was confirmed by transcriptional analysis and direct measurement of their relative levels in bacterial cells by tandem mass spectrometry analysis in multiple reaction monitoring scan mode. Conclusion: These evidences suggest that treatment with Esc(1-21)-1c in combination with antibiotics would increase the intracellular drug content making bacteria more susceptible to the antibiotic. Overall, these results highlight the importance of characterizing new molecules able to synergize with conventional antibiotics, paving the way for the development of alternative therapeutic strategies based on AMP/antibiotic formulations to counteract the emergence of resistant bacterial strains and increase the use of "old" antibiotics in medical practice.

Antibacterial mechanism of the novel antimicrobial peptide Jelleine-Ic and its efficacy in controlling Pseudomonas syringae pv. actinidiae in kiwifruit

BACKGROUND

Bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) poses a severe threat to kiwifruit production. Because of the insufficient efficacy and environmental safety of available treatments, novel antibacterial agents should be urgently developed. Antimicrobial peptides (AMPs) can be used as antimicrobials for disease control. In this study, we designed a novel AMP, Jelleine-Ic, and evaluated its antibacterial activity and mechanism of action against Psa.

RESULTS

Jelleine-Ic with a half-maximal effective concentration of 1.67 μg/mL exhibited stronger antibacterial activity than did parent Jelleine-I. Jelleine-Ic targeted the Psa membrane, increased membrane permeabilization and dissipated membrane potential, resulting in calcium leakage. Electron microscopy revealed that Jelleine-Ic disrupted cell morphology and caused intracellular alterations. Moreover, this AMP penetrated the cell membrane, bound to DNA, and reduced the expression of genes related to DNA replication and repair. Jelleine-Ic also reduced esterase activity and induced intracellular reactive oxygen species generation. This peptide inhibited the development of Psa canker. The control efficiency of Jelleine-Ic against Psa in the leaf discs and leaves of kiwifruit was 81.83% and 70.53%, respectively, which was superior to that of the commercial agricultural streptomycin. Furthermore, Jelleine-Ic upregulated the expression of kiwifruit defense genes (PR-10 and WRKY70a).

CONCLUSION

Jelleine-Ic effectively controls Psa in vitro and in vivo, and may be developed as a bactericide for plant disease control. © 2023 Society of Chemical Industry.

Computationally Designed AMPs with Antibacterial and Antibiofilm Activity against MDR Acinetobacter baumannii

The discovery of new antimicrobials is necessary to combat multidrug-resistant (MDR) bacteria, especially those that infect wounds and form prodigious biofilms, such as Acinetobacter baumannii. Antimicrobial peptides (AMPs) are a promising class of new therapeutics against drug-resistant bacteria, including gram-negatives. Here, we utilized a computational AMP design strategy combining database filtering technology plus positional analysis to design a series of novel peptides, named HRZN, designed to be active against A. baumannii. All of the HRZN peptides we synthesized exhibited antimicrobial activity against three MDR A. baumannii strains with HRZN-15 being the most active (MIC 4 µg/mL). This peptide also inhibited and eradicated biofilm of A. baumannii strain AB5075 at 8 and 16 µg/mL, which is highly effective. HRZN-15 permeabilized and depolarized the membrane of AB5075 rapidly, as demonstrated by the killing kinetics. HRZN 13 and 14 peptides had little to no hemolysis activity against human red blood cells, whereas HRZN-15, -16, and -17 peptides demonstrated more significant hemolytic activity. HRZN-15 also demonstrated toxicity to waxworms. Further modification of HRZN-15 could result in a new peptide with an improved toxicity profile. Overall, we successfully designed a set of new AMPs that demonstrated activity against MDR A. baumannii using a computational approach.

ApoE Mimetic Peptide COG1410 Exhibits Strong Additive Interaction with Antibiotics Against Mycobacterium smegmatis

Background

Drug-resistant tuberculosis (TB) is an emerging threat to public health worldwide. Antimicrobial peptide (AMP) is a promising solution to solve the antimicrobial resistance crisis. The apolipoprotein E mimetic peptide COG1410 has been confirmed to simultaneously have neuroprotective, anti-inflammatory, and antibacterial activity. However, whether it is effective to inhibit growth of mycobacteria has not been investigated yet.

Methods

The peptide COG1410 was synthesized with conventional solid-phase peptide synthesis and qualified by HPLC and mass spectrometry. Micro-dilution method was used to determine the minimal inhibitory concentration. A time-kill assay was used to determine the bactericidal dynamics of antimicrobial peptide and relative antibiotics. Static biofilm formation was conducted in 24-well plate and the biofilm was separated from planktonic cells and collected. The mechanism of action of COG1410 was explored by TEM observation and ATP leak assay. The localization of COG1410 was observed by confocal laser scan microscopy. The drug-drug interaction was determined by a checkerboard assay.

Results

COG1410 was a potent bactericidal agent against M. smegmatis in vitro and within the macrophages with MIC 16 μg/mL, but invalid against M. abscess and M. tuberculosis. A time-kill assay showed that COG1410 killed M. smegmatis as potent as clarithromycin, but faster than LL-37, another short synthetic cationic peptide. 1× MIC COG1410 almost reduced 90% biofilm formation of M. smegmatis. Additionally, COG1410 was able to penetrate the cell membrane of macrophage and inhibit intracellular M. smegmatis growth. TEM observation and ATP leak assay found that COG1410 disrupted cell membrane and caused release of cell contents. Confocal fluorescence microscopy showed that FITC-COG1410 aggregated around cell membrane instead of entering the cytoplasm. Although COG1410 had relative high cytotoxicity, it exhibited strong additive interaction with regular anti-TB antibiotics, which reduced the working concentration of COG1410 and expanding safety window. After 30 passages, there was no induced drug resistance for COG1410.

Conclusion

COG1410 was a novel and potent AMP against M. smegmatis by disrupting the integrity of cell membrane.

Membrane-Active Cyclic Amphiphilic Peptides: Broad-Spectrum Antibacterial Activity Alone and in Combination with Antibiotics

We designed a library of 24 cyclic peptides containing arginine (R) and tryptophan (W) residues in a sequential manner [R_nW_n] (n = 2-7) to study the impact of the hydrophilic/hydrophobic ratio, charge, and ring size on the antibacterial activity against Gram-positive and Gram-negative strains. Among peptides, 5a and 6a demonstrated the highest antimicrobial activity. In combination with 11 commercially available antibiotics, 5a and 6a showed remarkable synergism against a large panel of resistant pathogens. Hemolysis (HC₅₀ = 340 μg/mL) and cell viability against mammalian cells demonstrated the selective lethal action of 5a against bacteria over mammalian cells. Calcein dye leakage and scanning electron microscopy studies revealed the membranolytic effect of 5a. Moreover, the stability in human plasma (t_1/2 = 3 h) and the negligible ability of pathogens to develop resistance further reflect the potential of 5a for further development as a peptide-based antibiotic.

Effects of Medicinal Leech-Related Cationic Antimicrobial Peptides on Human Blood Cells and Plasma

Cationic antimicrobial peptides (CAMPs) are considered as next-generation antibiotics with a lower probability of developing bacterial resistance. In view of potential clinical use, studies on CAMP biocompatibility are important. This work aimed to evaluate the behavior of synthetic short CAMPs (designed using bioinformatic analysis of the medicinal leech genome and microbiome) in direct contact with blood cells and plasma. Eight CAMPs were included in the study. Hemolysis and lactate dehydrogenase assays showed that the potency to disrupt erythrocyte, neutrophil and mononuclear cell membranes descended in the order pept_1 > pept_3 ~ pept_5 > pept_2 ~ pept_4. Pept_3 caused both cell lysis and aggregation. Blood plasma and albumin inhibited the CAMP-induced hemolysis. The chemiluminescence method allowed the detection of pept_3-mediated neutrophil activation. In plasma coagulation assays, pept_3 prolonged the activated partial thromboplastin time (APTT) and prothrombin time (at 50 μM by 75% and 320%, respectively). Pept_3 was also capable of causing fibrinogen aggregation. Pept_6 prolonged APTT (at 50 μM by 115%). Pept_2 was found to combine higher bactericidal activity with lower effects on cells and coagulation. Our data emphasize the necessity of investigating CAMP interaction with plasma.

Synergistic Antimicrobial Effect of Antimicrobial Peptides CATH-1, CATH-3, and PMAP-36 With Erythromycin Against Bacterial Pathogens

With the increasing bacterial resistance to traditional antibiotics, there is an urgent need for the development of alternative drugs or adjuvants of antibiotics to enhance antibacterial efficiency. The combination of antimicrobial peptides (AMPs) and traditional antibiotics is a potential alternative to enhance antibacterial efficiency. In this study, we investigated the synergistic bactericidal effect of AMPs, including chicken (CATH-1,−2,−3, and -B1), mice (CRAMP), and porcine (PMAP-36 and PR-39) in combination with conventional antibiotics containing ampicillin, tetracycline, gentamicin, and erythromycin against Staphylococcus aureus, Salmonella enteritidis, and Escherichia coli. The results showed that the minimum bactericidal concentration (MBC) of CATH-1,−3 and PMAP-36 was lower than 10 μM, indicating that these three AMPs had good bacterial activity against S. aureus, S. enteritidis, and E. coli. Then, the synergistic antibacterial activity of AMPs and antibiotics combination was determined by the fractional bactericidal concentration index (FBCI). The results showed that the FBCI of AMPs (CATH-1,−3 and PMAP-36) and erythromycin was lower than 0.5 against bacterial pathogens, demonstrating that they had a synergistic bactericidal effect. Furthermore, the time-killing kinetics of AMPs (CATH-1,−3 and PMAP-36) in combination with erythromycin showed that they had a continuous killing effect on bacteria within 3 h. Notably, the combination showed lower hemolytic activity and cytotoxicity to mammal cells compared to erythromycin and peptide alone treatment. In addition, the antibacterial mechanism of CATH-1 and erythromycin combination against E. coli was studied. The results of the scanning electron microscope showed that CATH-1 enhanced the antibacterial activity of erythromycin by increasing the permeability of bacterial cell membrane. Moreover, the results of bacterial migration movement showed that the combination of CATH-1 and erythromycin significantly inhibits the migration of E. coli. Finally, drug resistance analysis was performed and the results showed that CATH-1 delayed the emergence of E. coli resistance to erythromycin. In conclusion, the combination of CATH-1 and erythromycin has synergistic antibacterial activity and reduces the emergence of bacterial drug resistance. Our study provides valuable information to develop AMPs as potential substitutes or adjuvants for traditional antibiotics.

Identification and Functional Characterization of Peptides With Antimicrobial Activity From the Syphilis Spirochete, Treponema pallidum

The etiological agent of syphilis, Treponema pallidum ssp. pallidum, is a highly invasive “stealth” pathogen that can evade the host immune response and persist within the host for decades. This obligate human pathogen is adept at establishing infection and surviving at sites within the host that have a multitude of competing microbes, sometimes including pathogens. One survival strategy employed by bacteria found at polymicrobial sites is elimination of competing microorganisms by production of antimicrobial peptides (AMPs). Antimicrobial peptides are low molecular weight proteins (miniproteins) that function directly via inhibition and killing of microbes and/or indirectly via modulation of the host immune response, which can facilitate immune evasion. In the current study, we used bioinformatics to show that approximately 7% of the T. pallidum proteome is comprised of miniproteins of 150 amino acids or less with unknown functions. To investigate the possibility that AMP production is an unrecognized defense strategy used by T. pallidum during infection, we developed a bioinformatics pipeline to analyze the complement of T. pallidum miniproteins of unknown function for the identification of potential AMPs. This analysis identified 45 T. pallidum AMP candidates; of these, Tp0451a and Tp0749 were subjected to further bioinformatic analyses to identify AMP critical core regions (AMPCCRs). Four potential AMPCCRs from the two predicted AMPs were identified and peptides corresponding to these AMPCCRs were experimentally confirmed to exhibit bacteriostatic and bactericidal activity against a panel of biologically relevant Gram-positive and Gram-negative bacteria. Immunomodulation assays performed under inflammatory conditions demonstrated that one of the AMPCCRs was also capable of differentially regulating expression of two pro-inflammatory chemokines [monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8)]. These findings demonstrate proof-of-concept for our developed AMP identification pipeline and are consistent with the novel concept that T. pallidum expresses AMPs to defend against competing microbes and modulate the host immune response.

Amphiphilic cyclic peptide [W4KR5]-Antibiotics combinations as broad-spectrum antimicrobial agents

Linear and cyclic amphiphilic peptides, (W₄KR₅) and [W₄KR₅], were evaluated as antibacterial agents against Gram-positive and Gram-negative bacteria, including four multi-drug resistant strains and the corresponding four non-resistant strains. Cyclic peptide [W₄KR₅] showed higher antibacterial activity than the linear (W₄KR₅) counterpart. Cyclic [W₄KR₅] was subjected to combination (physical mixture or covalent conjugation) with meropenem as a model antibiotic to study the impact of the combination on antimicrobial activity. A physical mixture of meropenem and [W₄KR₅] showed synergistic antibacterial activity against Gram-negative P. aeruginosa (ATCC BAA-1744) and P. aeruginosa (ATCC 27883) strains. [W₄KR₅] was further subjected to extensive antibacterial studies against additional 10 bacteria strains, showing significant antibacterial efficacy against Gram-positive bacteria strains. Combinations studies of [W₄KR₅] with an additional 9 commercially available antibiotics showed significant enhancement in antibacterial activity for all tested combinations, especially with tetracycline, tobramycin, levofloxacin, clindamycin, daptomycin, polymyxin, kanamycin, and vancomycin. Time-kill kinetics assay and flow cytometry results exhibited that [W₄KR₅] had a time-dependent synergistic effect and membrane disruption property. These data indicate that [W₄KR₅] improves the antibacterial activity, presumably by facilitating the internalization of antibiotics and their interaction with the intracellular targets. This study introduces a potential strategy for treating multidrug-resistant pathogens by combining [W₄KR₅] and a variety of classical antibiotics to improve the antibacterial effectiveness.

Exploring synergy and its role in antimicrobial peptide biology

Antimicrobial peptides will be an essential component in combating the escalating issue of antibiotic resistance. Identifying synergistic combinations of two or more substances will increase the value of these peptides further. Several potential pitfalls in conducting synergy testing with peptides are discussed in detail. As case studies, we describe observations of AMP synergy with peptides, antibiotics, and metal ions as well as some of the mechanistic details that have been uncovered. The Bliss and Loewe models for synergy are presented prior to recommending protocols for conducting checkerboard, minimal inhibitory concentration, and time-kill assays. Establishing mechanisms of action and exploring the potential for resistance will be crucial to translate these studies into the clinic.

Machine Learning Prediction of Antimicrobial Peptides

Antibiotic resistance constitutes a global threat and could lead to a future pandemic. One strategy is to develop a new generation of antimicrobials. Naturally occurring antimicrobial peptides (AMPs) are recognized templates and some are already in clinical use. To accelerate the discovery of new antibiotics, it is useful to predict novel AMPs from the sequenced genomes of various organisms. The antimicrobial peptide database (APD) provided the first empirical peptide prediction program. It also facilitated the testing of the first machine-learning algorithms. This chapter provides an overview of machine-learning predictions of AMPs. Most of the predictors, such as AntiBP, CAMP, and iAMPpred, involve a single-label prediction of antimicrobial activity. This type of prediction has been expanded to antifungal, antiviral, antibiofilm, anti-TB, hemolytic, and anti-inflammatory peptides. The multiple functional roles of AMPs annotated in the APD also enabled multi-label predictions (iAMP-2L, MLAMP, and AMAP), which include antibacterial, antiviral, antifungal, antiparasitic, antibiofilm, anticancer, anti-HIV, antimalarial, insecticidal, antioxidant, chemotactic, spermicidal activities, and protease inhibiting activities. Also considered in predictions are peptide posttranslational modification, 3D structure, and microbial species-specific information. We compare important amino acids of AMPs implied from machine learning with the frequently occurring residues of the major classes of natural peptides. Finally, we discuss advances, limitations, and future directions of machine-learning predictions of antimicrobial peptides. Ultimately, we may assemble a pipeline of such predictions beyond antimicrobial activity to accelerate the discovery of novel AMP-based antimicrobials.

Synergistic effect and antibiofilm activity of an antimicrobial peptide with traditional antibiotics against multi-drug resistant bacteria

Combined treatment of AMPs with classical antibiotics has gained interest because it often results in a synergistic antibacterial effect. We demonstrated here that Pt5-1c, an AMP derived from phosvitin, had antibacterial activity against the MDR bacteria (S. aureus USA500, E. coli 577 and K. pneumoniae 2182) in the presence of serum. On this basis, we showed that Pt5-1c was synergistically active with traditional antibiotics (oxacillin, vancomycin, streptomycin and azithromycin) against the three MDR bacteria growing as biofilms in vitro and in vivo. Moreover, Pt5-1c restored sensitivity of S. aureus USA500 to oxacillin and vancomycin, E. coli 577 to streptomycin and K. pneumoniae 2182 to azithromycin. Importantly, long-term exposure to Pt5-1c did not give rise to antimicrobial resistance. Collectively, these data not only suggest a promising combinatorial therapy strategy to combat antibiotics-tolerant infections but also present a possibility of Pt5-1c being used to prolong the application of antibiotics including oxacillin, vancomycin, streptomycin and azithromycin, that are under threat of becoming ineffective due to antibiotic resistance.

Genetic Determinants of Antibiotic Resistance in Francisella

Tularemia, caused by Francisella tularensis, is endemic to the northern hemisphere. This zoonotic organism has historically been developed into a biological weapon. For this Tier 1, Category A select agent, it is important to expand our understanding of its mechanisms of antibiotic resistance (AMR). Francisella is unlike many Gram-negative organisms in that it does not have significant plasmid mobility, and does not express AMR mechanisms on plasmids; thus plasmid-mediated resistance does not occur naturally. It is possible to artificially introduce plasmids with AMR markers for cloning and gene expression purposes. In this review, we survey both the experimental research on AMR in Francisella and bioinformatic databases which contain genomic and proteomic data. We explore both the genetic determinants of intrinsic AMR and naturally acquired or engineered antimicrobial resistance as well as phenotypic resistance in Francisella. Herein we survey resistance to beta-lactams, monobactams, carbapenems, aminoglycosides, tetracycline, polymyxins, macrolides, rifampin, fosmidomycin, and fluoroquinolones. We also highlight research about the phenotypic AMR difference between planktonic and biofilm Francisella. We discuss newly developed methods of testing antibiotics against Francisella which involve the intracellular nature of Francisella infection and may better reflect the eventual clinical outcomes for new antibiotic compounds. Understanding the genetically encoded determinants of AMR in Francisella is key to optimizing the treatment of patients and potentially developing new antimicrobials for this dangerous intracellular pathogen.

Isolation, characterization of galactose-specific lectin from Odoiporus longicollis and its antibacterial and anticancer activities

Lectins are renowned hemagglutinins and multivalent proteins with a well known quality for sugar-binding specificity that participate significantly in invertebrate defense functions. Studies on biological activity of lectin from coleopteran insect are very scarce. In this study, lectin from the hemolymph in the grub of banana pest, Odoiporus longicollis was subjected to purification, biochemical and functional characterizations. The lectin was purified by PEG precipitation and ion-exchange chromatography using Q-Sepharose as a matrix. The purified lectin showed hemagglutination activity against rat erythrocytes, heat-labile, cation independent and insensitive to EDTA. Further, the carbohydrate affinity of this lectin was found with mannitol, adonitol, L-arabinose, L-rhamnose, D-galactose and sorbitol. The native form of purified lectin was calculated as 360 kDa by FPLC system. Denatured gel electrophoresis of the purified lectin consisted of five distinct polypeptides with molecular weights approximately 160, 60, 52, 40 and 38 kDa, respectively. The amino acid sequences obtained through peptide mass fingerprinting analysis exhibited homologies to the known conserved regions of galactose binding lectins. Further, the purified lectin exhibited bacterial inhibition with LPS from Serratia marcescens. In addition, isolated lectin also exerted bacterial agglutination, antibacterial and anti-proliferative activity against Mycobacterium smegmatis, Bacillus pumilus and Neuro 2a cell line, respectively.

Trp-Containing Antibacterial Peptides Impair Quorum Sensing and Biofilm Development in Multidrug-Resistant Pseudomonas aeruginosa and Exhibit Synergistic Effects With Antibiotics

Pseudomonas aeruginosa uses quorum sensing (QS) to control virulence, biofilm formation and antibiotic efflux pump expression. The development of effective small molecules targeting the QS system and biofilm formation represents a novel attractive strategy. In this present study, the effects of a series of Trp-containing peptides on the QS-regulated virulence and biofilm development of multidrug-resistant P. aeruginosa, as well as their synergistic antibacterial activity with three classes of traditional chemical antibiotics were investigated. The results showed that Trp-containing peptides at low concentrations reduced the production of QS-regulated virulence factors by downregulating the gene expression of both the las and rhl systems in the strain MRPA0108. Biofilm formation was inhibited in a concentration-dependent manner, which was associated with extracellular polysaccharide production inhibition by downregulating pelA, algD, and pslA transcription. These changes correlated with alterations in the extracellular production of pseudomonal virulence factors and swarming motility. In addition, the combination of Trp-containing peptides at low concentration with the antibiotics ceftazidime and piperacillin provided synergistic effects. Notably, L11W and L12W showed the highest synergy with ceftazidime and piperacillin. A mechanistic study demonstrated that the Trp-containing peptides, especially L12W, significantly decreased β-lactamase activity and expression of efflux pump genes OprM, MexX, and MexA, resulting in a reduction in antibiotic efflux from MRPA0108 cells and thus increasing the antibacterial activity of these antibiotics against MRPA0108.

Re-sensitization of Mycobacterium smegmatis to Rifampicin Using CRISPR Interference Demonstrates Its Utility for the Study of Non-essential Drug Resistance Traits

A greater understanding of the genes involved in antibiotic resistance in Mycobacterium tuberculosis (Mtb) is necessary for the design of improved therapies. Clustered regularly interspaced short palindromic repeat interference (CRISPRi) has been previously utilized in mycobacteria to identify novel drug targets by the demonstration of gene essentiality. The work presented here shows that it can also be usefully applied to the study of non-essential genes involved in antibiotic resistance. The expression of an ADP-ribosyltransferase (Arr) involved in rifampicin resistance in Mycobacterium smegmatis was silenced using CRISPRi and the impact on rifampicin susceptibility was measured. Gene silencing resulted in a decrease in the minimum inhibitory concentration (MIC) similar to that previously reported in an arr deletion mutant. There is contradictory evidence for the toxicity of Streptococcus pyogenes dCas9 (dCas9_Spy) in the literature. In this study the expression of dCas9_Spy in M. smegmatis showed no impact on viability. Silencing was achieved with concentrations of the aTc inducer lower than previously described and with shorter induction times. Finally, designing small guide RNAs (sgRNAs) that target transcription initiation, or the early stages of elongation had the most impact on rifampicin susceptibility. This study demonstrates that CRISPRi based gene silencing can be as impactful as gene deletion for the study of non-essential genes and further contributes to the knowledge on the design and induction of sgRNAs for CRISPRi. This approach can be applied to other non-essential antimicrobial resistance genes such as drug efflux pumps.

How Insertion of a Single Tryptophan in the N-Terminus of a Cecropin A-Melittin Hybrid Peptide Changes Its Antimicrobial and Biophysical Profile

In the era of antibiotic resistance, there is an urgent need for efficient antibiotic therapies to fight bacterial infections. Cationic antimicrobial peptides (CAMP) are promising lead compounds given their membrane-targeted mechanism of action, and high affinity towards the anionic composition of bacterial membranes. We present a new CAMP, W-BP100, derived from the highly active BP100, holding an additional tryptophan at the N-terminus. W-BP100 showed a broader antibacterial activity, demonstrating a potent activity against Gram-positive strains. Revealing a high partition constant towards anionic over zwitterionic large unilamellar vesicles and inducing membrane saturation at a high peptide/lipid ratio, W-BP100 has a preferential location for hydrophobic environments. Contrary to BP100, almost no aggregation of anionic vesicles is observed around saturation conditions and at higher concentrations no aggregation is observed. With these results, it is possible to state that with the incorporation of a single tryptophan to the N-terminus, a highly active peptide was obtained due to the π-electron system of tryptophan, resulting in negatively charged clouds, that participate in cation-π interactions with lysine residues. Furthermore, we propose that W-BP100 action can be achieved by electrostatic interactions followed by peptide translocation.

Excellent synergistic activity of a designed membrane acting pyridinium containing antimicrobial cationic N-acylethanolamine with isoniazid against mycobacterium

cNAEs lower the MIC of isoniazid without compromising antimycobacterial activity.

Komodo-dragon cathelicidin-inspired peptides are antibacterial against carbapenem-resistant Klebsiella pneumoniae

Introduction.The rise of carbapenem-resistant enterobacteriaceae (CRE) is a growing crisis that requires development of novel therapeutics.

Hypothesis.To this end, cationic antimicrobial peptides (CAMPs) represent a possible source of new potential therapeutics to treat difficult pathogens such as carbapenem-resistantKlebsiella pneumoniae(CRKP), which has gained resistance to many if not all currently approved antibiotics, making treatment difficult.

Aim.To examine the anti-CRKP antimicrobial activity of the predicted cathelicidins derived fromVaranus komodoensis(Komodo dragon) as well as synthetic antimicrobial peptides that we created.

Methodology.We determined the minimum inhibitory concentrations of the peptides against CRKP. We also characterized the abilities of these peptides to disrupt the hyperpolarization of the bacterial membrane as well as their ability to form pores in the membrane.

Results.We did not observe significant anti-CRKP activity for the predicted native Komodo cathelicidin peptides. We found that the novel peptides DRGN-6,-7 and -8 displayed significant antimicrobial activity against CRKP with MICs of 4–8 µg ml−1. DRGN-6 peptide was the most effective peptide against CRKP. Unfortunately, these peptides showed higher than desired levels of hemolysis, althoughin vivotesting in the waxwormGalleria mellonellashowed no mortality associated with treatment by the peptide; however, CRKP-infected waxworms treated with peptide did not show an improvement in survival.

Conclusion.Given the challenges of treating CRKP, identification of peptides with activity against it represents a promising avenue for further research. Given DRGN-6′s similar level of activity to colistin, DRGN-6 is a promising template for the development of novel antimicrobial peptide-based therapeutics.

Novel Antimicrobial Peptide from Temporin L in The Treatment of Staphylococcus pseudintermedius and Malassezia pachydermatis in Polymicrobial Inter-Kingdom Infection

Interkingdom polymicrobial diseases are caused by different microorganisms that colonize the same niche, as in the case of yeast-bacteria coinfections. The latter are difficult to treat due the absence of any common therapeutic target for their elimination, both in animals and humans. Staphylococcus pseudintermedius and Malassezia pachydermatis belong to distinct kingdoms. They can colonize the same skin district or apparatus being the causative agents of fastidious pet animals’ pathologies. Here we analysed the antimicrobial properties of a panel of 11 peptides, derived from temporin L, against Malassezia pachydermatis. Only peptide 8 showed the best mycocidal activity at 6.25 μM. Prolonged application of peptide 8 did not cause M. pachydermatis drug-resistance. Peptide 8 was also able to inhibit the growth of Staphylococcus pseudintermedius, regardless of methicillin resistance, at 1.56 μM for methicillin-susceptible S. pseudintermedius (MSSP) and 6.25 μM for methicillin-resistant S. pseudintermedius (MRSP). Of interest, peptide 8 increased the susceptibility of MRSP to oxacillin. Oxacillin MIC value reduction was of about eight times when used in combination with peptide 8. Finally, the compound affected the vitality of bacteria embedded in S. pseudintermedius biofilm. In conclusion, peptide 8 might represent a valid therapeutic alternative in the treatment of interkingdom polymicrobial infections, also in the presence of methicillin-resistant bacteria.

Metal-Peptide Complexes as Promising Antibiotics to Fight Emerging Drug Resistance: New Perspectives in Tuberculosis

In metal-peptide interactions, cations form stable complexes through bonds with coordinating groups as side chains of amino acids. These compounds, among other things, exert a wide variety of antimicrobial activities through structural changes of peptides upon metal binding and redox chemistry. They exhibit different mechanisms of action (MOA), including the modification of DNA/RNA, protein and cell wall synthesis, permeabilization and modulation of gradients of cellular membranes. Nowadays, the large increase in antibiotic resistance represents a crucial problem to limit progression at the pandemic level of the diseases that seemed nearly eradicated, such as tuberculosis (Tb). Mycobacterium tuberculosis (Mtb) is intrinsically resistant to many antibiotics due to chromosomal mutations which can lead to the onset of novel strains. Consequently, the maximum pharmaceutical effort should be focused on the development of new therapeutic agents and antimicrobial peptides can represent a valuable option as a copious source of potential bioactive compounds. The introduction of a metal center can improve chemical diversity and hence specificity and bioavailability while, in turn, the coordination to peptides of metal complexes can protect them and enhance their poor water solubility and air stability: the optimization of these parameters is strictly required for drug prioritization and to obtain potent inhibitors of Mtb infections with novel MOAs. Here, we present a panoramic review of the most recent findings in the field of metal complex-peptide conjugates and their delivery systems with the potential pharmaceutical application as novel antibiotics in Mtb infections.

Hitchhiking with Nature: Snake Venom Peptides to Fight Cancer and Superbugs

Abstract

For decades, natural products in general and snake venoms (SV) in particular have been a rich source of bioactive compounds for drug discovery, and they remain a promising substrate for therapeutic development. Currently, a handful of SV-based drugs for diagnosis and treatment of various cardiovascular disorders and blood abnormalities are on the market. Likewise, far more SV compounds and their mimetics are under investigation today for diverse therapeutic applications, including antibiotic-resistant bacteria and cancer. In this review, we analyze the state of the art regarding SV-derived compounds with therapeutic potential, focusing on the development of antimicrobial and anticancer drugs. Specifically, information about SV peptides experimentally validated or predicted to act as antimicrobial and anticancer peptides (AMPs and ACPs, respectively) has been collected and analyzed. Their principal activities both in vitro and in vivo, structures, mechanisms of action, and attempts at sequence optimization are discussed in order to highlight their potential as drug leads.

Key Contribution

This review describes the state of the art in snake venom-derived peptides and their therapeutic applications. This work reinforces the potential of snake venom components as therapeutic agents, particularly in the quest for new antimicrobial and anticancer drugs.

Antimicrobial peptides against drug resistant Mycobacterium abscessus

Mycobacterium abscessus (MAB) comprise rapidly growing, often multidrug-resistant (MDR), nontuberculous mycobacteria responsible for pulmonary and other infections in susceptible hosts. Antimicrobial peptides (APs) are natural and synthetic antimicrobials active against a range of microorganisms including mycobacteria. We evaluated APs activity against MAB reference and clinical strains. We observed minimal inhibitory concentrations of 1.6 to >50 μg/mL. Further work with the most active AP demonstrated protection of Acanthamoeba castellanii (AC) from killing by ingested MAB including MDR MAB strains. Antimicrobial peptides offer an attractive potential option for treatment of drug resistant treatment-refractory MAB.

Antimicrobial Activity of Protein Fraction from Naja ashei Venom Against Staphylococcus epidermidis

One of the key problems of modern infectious disease medicine is the growing number of drug-resistant and multi-drug-resistant bacterial strains. For this reason, many studies are devoted to the search for highly active antimicrobial substances that could be used in therapy against bacterial infections. As it turns out, snake venoms are a rich source of proteins that exert a strong antibacterial effect, and therefore they have become an interesting research material. We analyzed Naja ashei venom for such antibacterial properties, and we found that a specific composition of proteins can act to eliminate individual bacterial cells, as well as the entire biofilm of Staphylococcus epidermidis. In general, we used ion exchange chromatography (IEX) to obtain 10 protein fractions with different levels of complexity, which were then tested against certified and clinical strains of S. epidermidis. One of the fractions (F2) showed exceptional antimicrobial effects both alone and in combination with antibiotics. The protein composition of the obtained fractions was determined using mass spectrometry techniques, indicating a high proportion of phospholipases A₂, three-finger toxins, and L-amino acids oxidases in F2 fraction, which are most likely responsible for the unique properties of this fraction. Moreover, we were able to identify a new group of low abundant proteins containing the Ig-like domain that have not been previously described in snake venoms.

Synergistic Antibacterial Activity of Designed Trp-Containing Antibacterial Peptides in Combination With Antibiotics Against Multidrug-Resistant Staphylococcus epidermidis

Multidrug resistance among various bacterial strains is leading to worldwide resistance to a wide range of antibiotics. Combination therapy involving current antibiotics and other biological or chemical molecules represents an attractive novel strategy. In this study, we investigated the synergistic antibacterial activity of a series of Trp-containing antimicrobial peptides (AMPs) with four classes of traditional chemical antibiotics that are inactive against multidrug-resistant Staphylococcus epidermidis (MRSE) in vitro and in vivo. Among the antibiotics that we studied, penicillin, ampicillin and erythromycin showed a distinct synergistic effect in combination with all of the Trp-containing AMPs, represented by a fractional inhibitory concentration index (FICI) of <0.5. The antibacterial activities were noticeably improved, with 32-to 64-fold reductions in the MIC values for ampicillin and 16- to 32-fold reductions in the MIC values for erythromycin and penicillin. Tetracycline showed synergistic activity with only I1WL5W but additive activity with L11W, L12W, and I4WL5W. Ceftazidime exhibited additive activity with the Trp-containing peptides. In addition, the antibiotics in combination with the peptide significantly inhibited biofilm formation by MRSE 1208. A mechanistic study demonstrated that the Trp-containing peptides, especially I1WL5W and I4WL5W, which contain two tryptophan residues, disrupted bacterial inner and outer membranes, which promoted antibiotic delivery into the cytoplasm and access to cytoplasmic targets; however, L11W and L12W may have increased intracellular antibiotic concentrations by decreasing blaZ, tet(m) and msrA expression. Importantly, strong synergistic activity against the MRSE 1208 strain was observed for the combination of I1WL5W and penicillin in a mouse infection model. Thus, the combination of AMPs and traditional antibiotics could be a promising option for the prevention of acute and chronic infections caused by MRSE.

The Komodo dragon (Varanus komodoensis) genome and identification of innate immunity genes and clusters

Background

We report the sequencing, assembly and analysis of the genome of the Komodo dragon (Varanus komodoensis), the largest extant lizard, with a focus on antimicrobial host-defense peptides. The Komodo dragon diet includes carrion, and a complex milieu of bacteria, including potentially pathogenic strains, has been detected in the saliva of wild dragons. They appear to be unaffected, suggesting that dragons have robust defenses against infection. While little information is available regarding the molecular biology of reptile immunity, it is believed that innate immunity, which employs antimicrobial host-defense peptides including defensins and cathelicidins, plays a more prominent role in reptile immunity than it does in mammals. .

Results

High molecular weight genomic DNA was extracted from Komodo dragon blood cells. Subsequent sequencing and assembly of the genome from the collected DNA yielded a genome size of 1.6 Gb with 45x coverage, and the identification of 17,213 predicted genes. Through further analyses of the genome, we identified genes and gene-clusters corresponding to antimicrobial host-defense peptide genes. Multiple β-defensin-related gene clusters were identified, as well as a cluster of potential Komodo dragon ovodefensin genes located in close proximity to a cluster of Komodo dragon β-defensin genes. In addition to these defensins, multiple cathelicidin-like genes were also identified in the genome. Overall, 66 β-defensin genes, six ovodefensin genes and three cathelicidin genes were identified in the Komodo dragon genome.

Conclusions

Genes with important roles in host-defense and innate immunity were identified in this newly sequenced Komodo dragon genome, suggesting that these organisms have a robust innate immune system. Specifically, multiple Komodo antimicrobial peptide genes were identified. Importantly, many of the antimicrobial peptide genes were found in gene clusters. We found that these innate immunity genes are conserved among reptiles, and the organization is similar to that seen in other avian and reptilian species. Having the genome of this important squamate will allow researchers to learn more about reptilian gene families and will be a valuable resource for researchers studying the evolution and biology of the endangered Komodo dragon.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-6029-y) contains supplementary material, which is available to authorized users.

Exploiting chitosan and gold nanoparticles for antimycobacterial activity of in silico identified antimicrobial motif of human neutrophil peptide-1

The upsurge of drug resistant tuberculosis is major health threat globally. To counteract, antimicrobial peptides are being explored as possible alternatives. However, certain limitations of peptide-based drugs such as potential toxicity, high cost and relatively low stability need to be addressed to enhance their clinical applicability. Use of computer predicted short active motifs of AMPs along with nanotechnology could not only overcome the limitations of AMPs but also potentiate their antimicrobial activity. Therefore, present study was proposed to in silico identify short antimicrobial motif (Pep-H) of human neutrophil peptide-1 (HNP-1) and explore its antimycobacterial activity in free form and using nanoparticles-based delivery systems. Based on colony forming unit analysis, motif Pep-H led to killing of more than 90% M. tb in vitro at 10 μg/ml, whereas, similar activity against intracellularly growing M. tb was observed at 5 μg/ml only. Thereafter, chitosan (244 nm) and gold nanoparticles (20 nm) were prepared for Pep-H with both the formulations showing minimal effects on the viability of human monocyte derived macrophages (MDMs) and RBC integrity. The antimycobacterial activity of Pep-H against intracellular mycobacteria was enhanced in both the nanoformulations as evident by significant reduction in CFU (>90%) at 5-10 times lower concentrations than that observed for free Pep-H. Thus, Pep-H is an effective antimycobacterial motif of HNP-1 and its activity is further enhanced by chitosan and gold nanoformulations.

Application of Antimicrobial Peptides of the Innate Immune System in Combination With Conventional Antibiotics-A Novel Way to Combat Antibiotic Resistance?

Rapidly growing resistance of pathogenic bacteria to conventional antibiotics leads to inefficiency of traditional approaches of countering infections and determines the urgent need for a search of fundamentally new anti-infective drugs. Antimicrobial peptides (AMPs) of the innate immune system are promising candidates for a role of such novel antibiotics. However, some cytotoxicity of AMPs toward host cells limits their active implementation in medicine and forces attempts to design numerous structural analogs of the peptides with optimized properties. An alternative route for the successful AMPs introduction may be their usage in combination with conventional antibiotics. Synergistic antibacterial effects have been reported for a number of such combinations, however, the molecular mechanisms of the synergy remain poorly understood and little is known whether AMPs cytotoxicy for the host cells increases upon their application with antibiotics. Our study is directed to examination of a combined action of natural AMPs with different structure and mode of action (porcine protegrin 1, caprine bactenecin ChBac3.4, human alpha- and beta-defensins (HNP-1, HNP-4, hBD-2, hBD-3), human cathelicidin LL-37), and egg white lysozyme with varied antibiotic agents (gentamicin, ofloxacin, oxacillin, rifampicin, polymyxin B, silver nanoparticles) toward selected bacteria, including drug-sensitive and drug-resistant strains, as well as toward some mammalian cells (human erythrocytes, PBMC, neutrophils, murine peritoneal macrophages and Ehrlich ascites carcinoma cells). Using “checkerboard titrations” for fractional inhibitory concentration indexes evaluation, it was found that synergy in antibacterial action mainly occurs between highly membrane-active AMPs (e.g., protegrin 1, hBD-3) and antibiotics with intracellular targets (e.g., gentamicin, rifampcin), suggesting bioavailability increase as the main model of such interaction. In some combinations modulation of dynamics of AMP-bacterial membrane interaction in presence of the antibiotic was also shown. Cytotoxic effects of the same combinations toward normal eukaryotic cells were rarely synergistic. The obtained data approve that combined application of antimicrobial peptides with antibiotics or other antimicrobials is a promising strategy for further development of new approach for combating antibiotic-resistant bacteria by usage of AMP-based therapeutics. Revealing the conventional antibiotics that increase the activity of human endogenous AMPs against particular pathogens is also important for cure strategies elaboration.

Human salivary proteins and their peptidomimetics: Values of function, early diagnosis, and therapeutic potential in combating dental caries

Saliva contains a large number of proteins that play various crucial roles to maintain the oral health and tooth integrity. This oral fluid is proposed to be one of the most important host factors, serving as a special medium for monitoring aspects of microorganisms, diet and host susceptibility involved in the caries process. Extensive salivary proteomic and peptidomic studies have resulted in considerable advances in the field of biomarkers discovery for dental caries. These salivary biomarkers may be exploited for the prediction, diagnosis, prognosis and treatment of dental caries, many of which could also provide the potential templates for bioactive peptides used for the biomimetic management of dental caries, rather than repairing caries lesions with artificial materials. A comprehensive understanding of the biological function of salivary proteins as well as their derived biomimetic peptides with promising potential against dental caries has been long awaited. This review overviewed a collection of current literature and addressed the majority of different functions of salivary proteins and peptides with their potential as functional biomarkers for caries risk assessment and clinical prospects for the anti-caries application.

DNA scaffolds support stable and uniform peptide nanopores

The assembly of peptides into membrane-spanning nanopores might be promoted by scaffolds to pre-organize the structures. Such scaffolds could enable the construction of uniform pores of various sizes and pores with controlled permutations around a central axis. Here, we show that DNA nanostructures can serve as scaffolds to arrange peptides derived from the octameric polysaccharide transporter Wza to form uniform nanopores in planar lipid bilayers. Our ring-shaped DNA scaffold is assembled from short synthetic oligonucleotides that are connected to Wza peptides through flexible linkers. When scaffolded, the Wza peptides form conducting nanopores of which only octamers are stable and of uniform conductance. Removal of the DNA scaffold by cleavage of the linkers leads to a rapid loss of the nanopores from the lipid bilayer, which shows that the scaffold is essential for their stability. The DNA scaffold also adds functionality to the nanopores by enabling reversible and permanent binding of complementary tagged oligonucleotides near the nanopore entrance.

Antimicrobial peptides as an alternative to anti-tuberculosis drugs

Tuberculosis (TB) presently accounts for high global mortality and morbidity rates, despite the introduction four decades ago of the affordable and efficient four-drugs (isoniazid, rifampicin, pyrazinamide and ethambutol). Thus, a strong need exists for new drugs with special structures and uncommon modes of action to effectively overcome M. tuberculosis. Within this scope, antimicrobial peptides (AMPs), which are small, cationic and amphipathic peptides that comprise a section of the innate immune system, are currently the leading potential agents for the treatment of TB. Many studies have recently illustrated the capability of anti-mycobacterial peptides to disrupt the normal mycobacterial cell wall function through various modes, thereby interacting with the intracellular targets, as well as encompassing nucleic acids, enzymes and organelles. This review presents a wide array of antimicrobial activities, alongside the associated properties of the AMPs that could be utilized as potential agents in therapeutic tactics for TB treatment.

The synthetic human beta-defensin-3 C15 peptide exhibits antimicrobial activity against Streptococcus mutans, both alone and in combination with dental disinfectants

Streptococcus mutans is a major etiologic agent of human dental caries that forms biofilms on hard tissues in the human oral cavity, such as tooth and dentinal surfaces. Human β-defensin-3 (HBD3) is a 45-amino-acid natural antimicrobial peptide that has broad spectrum antimicrobial activity against bacteria and fungi. A synthetic peptide consisting of the C-terminal 15 amino acids of HBD3 (HBD3-C15) was recently shown to be sufficient for its antimicrobial activity. Thus, clinical applications of this peptide have garnered attention. In this study, we investigated whether HBD3-C15 inhibits the growth of the representative cariogenic pathogen Streptococcus mutans and its biofilm formation. HBD3-C15 inhibited bacterial growth, exhibited bactericidal activity, and attenuated bacterial biofilm formation in a dose-dependent manner. HBD3-C15 potentiated the bactericidal and anti-biofilm activity of calcium hydroxide (CH) and chlorhexidine digluconate (CHX), which are representative disinfectants used in dental clinics, against S. mutans. Moreover, HBD3-C15 showed antimicrobial activity by inhibiting biofilm formation by S. mutans and other dentinophilic bacteria such as Enterococcus faecalis and Streptococcus gordonii, which are associated with dental caries and endodontic infection, on human dentin slices. These effects were observed for HBD3-C15 alone and for HBD3-C15 in combination with CH or CHX. Therefore, we suggest that HBD3-C15 is a potential alternative or additive disinfectant that can be used for the treatment of oral infectious diseases, including dental caries and endodontic infections.

Activity of human beta defensin-1 and its motif against active and dormant Mycobacterium tuberculosis

The ineffectiveness of anti-tuberculous therapy against dormant and drug-resistant mycobacteria demands scrutiny of alternative candidates like antimicrobial peptides having different mechanisms of action. The present study was designed to explore the activity of human beta defensin-1 (HBD-1) and its in silico identified short motif Pep-B against active and dormant Mycobacterium tuberculosis (M. tb) H37Rv. Activity of HBD-1 and Pep-B was determined against actively growing M. tb in vitro, inside monocyte-derived macrophages (MDMs) and dormant bacilli in in vitro potassium deficiency and human peripheral blood mononuclear cell (PBMC) granuloma models using colony-forming unit enumeration. The minimum inhibitory concentrations (MIC) of HBD-1 and Pep-B were found to be 2 and 20 μg/ml, respectively. These peptides also inhibited intracellular mycobacterial growth at concentrations lower than in vitro MICs along with increased IFN-γ levels. Although at higher concentration, HBD-1 (× 2 MIC) and Pep-B (× 2 MIC) led to decrease in in vitro dormant mycobacterial load as compared to rifampicin (× 25 MIC) and isoniazid (× 16 MIC). Similarly, both peptides showed higher killing efficacy against dormant mycobacteria inside granuloma as compared to rifampicin. Thus, the present study indicates that HBD-1 and its motif are effective antimicrobial players against both actively growing and dormant mycobacteria.

Activated Mesenchymal Stem Cells Interact with Antibiotics and Host Innate Immune Responses to Control Chronic Bacterial Infections

Chronic bacterial infections associated with biofilm formation are often difficult to resolve without extended courses of antibiotic therapy. Mesenchymal stem cells (MSC) exert antibacterial activity in vitro and in acute bacterial infection models, but their activity in chronic infection with biofilm models has not been previously investigated. Therefore, we studied the effects of MSC administration in mouse and dog models of chronic infections associated with biofilms. Mice with chronic Staphylococcus aureus implant infections were treated by i.v. administration of activated or non-activated MSC, with or without antibiotic therapy. The most effective treatment protocol was identified as activated MSC co-administered with antibiotic therapy. Activated MSC were found to accumulate in the wound margins several days after i.v. administration. Macrophages in infected tissues assumed an M2 phenotype, compared to untreated infections which contained predominately M1 macrophages. Bacterial killing by MSC was found to be mediated in part by secretion of cathelicidin and was significantly increased by antibiotics. Studies in pet dogs with spontaneous chronic multi drug-resistant wound infections demonstrated clearance of bacteria and wound healing following repeated i.v. administration of activated allogeneic canine MSC. Thus, systemic therapy with activated MSC may be an effective new, non-antimicrobial approach to treatment of chronic, drug-resistant infections.

Antimicrobial activity of mosquito cecropin peptides against Francisella

Francisella tularensis is the cause of the zoonotic disease tularemia. In Sweden and Scandinavia, epidemiological studies have implicated mosquitoes as a vector. Prior research has demonstrated the presence of Francisella DNA in infected mosquitoes but has not shown definitive transmission of tularemia from a mosquito to a mammalian host. We hypothesized that antimicrobial peptides, an important component of the innate immune system of higher organisms, may play a role in mosquito host-defense to Francisella. We established that Francisella sp. are susceptible to two cecropin antimicrobial peptides derived from the mosquito Aedes albopictus as well as Culex pipiens. We also demonstrated induced expression of Aedes albopictus antimicrobial peptide genes by Francisella infection C6/36 mosquito cell line. We demonstrate that mosquito antimicrobial peptides act against Francisella by disrupting the cellular membrane of the bacteria. Thus, it is possible that antimicrobial peptides may play a role in the inability of mosquitoes to establish an effective natural transmission of tularemia.

Peptides from American alligator plasma are antimicrobial against multi-drug resistant bacterial pathogens including Acinetobacter baumannii

BACKGROUND

Our group has developed a new process for isolating and identifying novel cationic antimicrobial peptides from small amounts of biological samples. Previously, we identified several active antimicrobial peptides from 100 μl of plasma from Alligator mississippiensis. These peptides were found to have in vitro antimicrobial activity against Pseudomonas aeruginosa and Staphylococcus aureus. In this work, we further characterize three of the novel peptides discovered using this process: Apo5, Apo6, and A1P.

RESULTS

We examined the activity of these peptides against multi-drug resistant strains and clinical isolates of common human pathogens. We investigated their structural characteristics using circular dichroism and tested for membrane disruption and DNA binding. These peptides were found to have strong in vitro activity against multi-drug resistant and clinically isolated strains of S. aureus, Escherichia coli, P. aeruginosa, and Acinetobacter baumannii. Apo5 and Apo6, peptides derived from alligator apolipoprotein C-1, depolarized the bacterial membrane. A1P, a peptide from the serpin proteinase inhibitor, did not permeabilize membranes. Performing circular dichroism analysis, Apo5 and Apo6 were found to be predominantly helical in SDS and TFE buffer, while A1P has significantly different structures in phosphate buffer, SDS, and TFE. None of these peptides were found to be hemolytic to sheep red blood cells or significantly cytotoxic up to 100 μg/ml after 24 h exposure.

CONCLUSIONS

Overall, we suggest that Apo5 and Apo6 have a different mode of action than A1P, and that all three peptides make promising candidates for the treatment of drug-resistant bacteria, such as A. baumannii.