Counter-ion effect on antistaphylococcal activity and cytotoxicity of selected antimicrobial peptides

Targeting Iron - Respiratory Reciprocity Promotes Bacterial Death

Discovering new bacterial signaling pathways offers unique antibiotic strategies. Here, through an unbiased resistance screen of 3,884 gene knockout strains, we uncovered a previously unknown non-lytic bactericidal mechanism that sequentially couples three transporters and downstream transcription to lethally suppress respiration of the highly virulent P. aeruginosa strain PA14 - one of three species on the WHO's 'Priority 1: Critical' list. By targeting outer membrane YaiW, cationic lacritin peptide 'N-104' translocates into the periplasm where it ligates outer loops 4 and 2 of the inner membrane transporters FeoB and PotH, respectively, to suppress both ferrous iron and polyamine uptake. This broadly shuts down transcription of many biofilm-associated genes, including ferrous iron-dependent TauD and ExbB1. The mechanism is innate to the surface of the eye and is enhanced by synergistic coupling with thrombin peptide GKY20. This is the first example of an inhibitor of multiple bacterial transporters.

Polymyxins with Potent Antibacterial Activity against Colistin-Resistant Pathogens: Fine-Tuning Hydrophobicity with Unnatural Amino Acids

In view of the increased prevalence of antimicrobial resistance among human pathogens, antibiotics against multidrug-resistant (MDR) bacteria are in urgent demand. In particular, the rapidly emerging resistance to last-resort antibiotic colistin, used for severe Gram-negative MDR infections, is critical. Here, a series of polymyxins containing unnatural amino acids were explored, and some analogues exhibited excellent antibacterial activity against Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. Hydrophobicity of the compounds within this series (as measured by retention in reversed-phase analytical HPLC) exhibited a discernible correlation with their antimicrobial activity. This trend was particularly pronounced for colistin-resistant pathogens. The most active compounds demonstrated competitive activity against a panel of Gram-negative pathogens, while exhibiting low in vitro cytotoxicity. Importantly, most of these hits also retained (or even had increased) potency against colistin-susceptible strains. These findings infer that fine-tuning hydrophobicity may enable the design of polymyxin analogues with favorable activity profiles.

The Study of Antistaphylococcal Potential of Omiganan and Retro-Omiganan Under Flow Conditions

Staphylococcus aureus is considered one of the leading pathogens responsible for infections in humans and animals. The heterogeneous nature of diseases caused by these bacteria is due to the occurrence of multiple strains, differentiated by several mechanisms of antibiotic resistance and virulence factors. One of these is the ability to form biofilm. Biofilm-associated bacteria exhibit a different phenotype that protects them from external factors such as the activity of immune system or antimicrobial substances. Moreover, it has been shown that the majority of persistent and recurrent infections are associated with the presence of the biofilm. Omiganan, an analog of indolicidin - antimicrobial peptide (AMP) derived from bovine neutrophil granules, was found to exhibit high antistaphylococcal and antibiofilm potential. Furthermore, its analog with a reversed sequence (retro-omiganan) was found to display enhanced activity against a variety of pathogens. Based on experience of our group, we found out that counterion exchange can improve the antistaphylococcal activity of AMPs. The aim of this study was to investigate the activity of both compounds against S. aureus biofilm under flow conditions. The advantage of this approach was that it offered the opportunity to form and characterize the biofilm under more controlled conditions. To do this, unique flow cells made of polydimethylsiloxane (PDMS) were developed. The activity against pre-formed biofilm as well as AMPs-treated bacteria was measured. Also, the incorporation of omiganan and retro-omiganan into the channels was conducted to learn whether or not it would inhibit the development of biofilm. The results of the microbiological tests ultimately confirmed the high potential of the omiganan and its retro-analog as well as the importance of counterion exchange in terms of antimicrobial examination. We found out that retro-omiganan trifluoroacetate had the highest biofilm inhibitory properties, however, acetates of both compounds exhibited the highest activity against planktonic and biofilm cultures. Moreover, the developed methodology of investigation under flow conditions allows the implementation of the studies under flow conditions to other compounds.

Complex-Forming Properties of the Anti-Inflammatory Sialorphin Derivative Palmitic Acid-Lysine-Lysine-Glutamine-Histidine-Asparagine-Proline-Arginine with Cu(II) Ions in an Aqueous Solution

The present work describes the complexation of the anti-inflammatory sialorphin derivative Pal-Lys-Lys-Gln-His-Asn-Pro-Arg (palmitic acid-lysine-lysine-glutamine-histidine-asparagine-proline-arginine) with Cu(II) ions in an aqueous solution, at a temperature of 25.0 ± 0.1 °C, over the whole pH range. The complexing properties were characterized by potentiometric and UV-Vis spectrophotometric methods. The potentiometric method was used to calculate the logarithms of the overall stability constants (log β) and the values of the stepwise dissociation constants (pKa) of the studied complexes. The percentage of each species formed in an aqueous solution was estimated from the species distribution curve as a function of pH. The absorbance (A) and molar absorption coefficient (ε) values for the Cu(II)-sialorphin derivative system were determined with UV-Vis spectroscopy. Our studies indicate that the sialorphin derivative forms stable complexes with Cu(II) ions, which may lead to future biological and therapeutic applications.

Molecular hybridization strategy for tuning bioactive peptide function

The physicochemical and structural properties of antimicrobial peptides (AMPs) determine their mechanism of action and biological function. However, the development of AMPs as therapeutic drugs has been traditionally limited by their toxicity for human cells. Tuning the physicochemical properties of such molecules may abolish toxicity and yield synthetic molecules displaying optimal safety profiles and enhanced antimicrobial activity. Here, natural peptides were modified to improve their activity by the hybridization of sequences from two different active peptide sequences. Hybrid AMPs (hAMPs) were generated by combining the amphipathic faces of the highly toxic peptide VmCT1, derived from scorpion venom, with parts of four other naturally occurring peptides having high antimicrobial activity and low toxicity against human cells. This strategy led to the design of seven synthetic bioactive variants, all of which preserved their structure and presented increased antimicrobial activity (3.1-128 μmol L-1). Five of the peptides (three being hAMPs) presented high antiplasmodial at 0.8 μmol L-1, and virtually no undesired toxic effects against red blood cells. In sum, we demonstrate that peptide hybridization is an effective strategy for redirecting biological activity to generate novel bioactive molecules with desired properties.

Understanding the Role of Self-Assembly and Interaction with Biological Membranes of Short Cationic Lipopeptides in the Effective Design of New Antibiotics

This study investigates short cationic antimicrobial lipopeptides composed of 2-4 amino acid residues and C12-C18 fatty acids attached to the N-terminal part of the peptides. The findings were discussed in the context of the relationship among biological activity, self-assembly, stability, and membrane interactions. All the lipopeptides showed the ability to self-assemble in PBS solution. In most cases, the critical aggregation concentration (CAC) much surpassed the minimal inhibitory concentration (MIC) values, suggesting that monomers are the main active form of lipopeptides. The introduction of β-alanine into the peptide sequence resulted in a compound with a high propensity to fibrillate, which increased the peptide stability and activity against S. epidermidis and C. albicans and reduced the cytotoxicity against human keratinocytes. The results of our study indicated that the target of action of lipopeptides is the bacterial membrane. Interestingly, the type of peptide counterion may affect the degree of penetration of the lipid bilayer. In addition, the binding of the lipopeptide to the membrane of Gram-negative bacteria may lead to the release of calcium ions necessary for stabilization of the lipopolysaccharide layer.

The Metabolic Potential of Endophytic Actinobacteria Associated with Medicinal Plant Thymus roseus as a Plant-Growth Stimulator

Bio-fertilizer practice considers not only economical but also environmentally friendly, sustainable agriculture. Endophytes can play important beneficiary roles in plant development, directly, indirectly, or synergistically. In this study, the majority of our endophytic actinobacteria were able to possess direct plant growth-promoting (PGP) traits, including auxin (88%), ammonia (96%), siderophore production (94%), and phosphate solubilization (24%), along with cell-wall degrading enzymes such as protease (75%), cellulase (81%), lipase (81%), and chitinase (18%). About 45% of tested strains have an inhibitory effect on the phytopathogen Fusarium oxysporum, followed by 26% for Verticillium dahlia. Overall, our results showed that strains XIEG63 and XIEG55 were the potent strains with various PGP traits that caused a higher significant increase (p ≤ 0.05) in length and biomass in the aerial part and roots of tomato and cotton, compared to the uninoculated plants. Our data showed that the greatest inhibition percentages of two phytopathogens were achieved due to treatment with strains XIEG05, XIEG07, XIEG45, and XIEG51. The GC-MS analysis showed that most of the compounds were mainly alkanes, fatty acid esters, phenols, alkenes, and aromatic chemicals and have been reported to have antifungal activity. Our investigation emphasizes that endophytic actinobacteria associated with medicinal plants might help reduce the use of chemical fertilization and potentially lead to increased agricultural productivity and sustainability.

The impact of counterions in biological activity: case study of antibacterial alkylguanidino ureas

Abstract

Trifluoroacetic acid (TFA), due to its strong acidity and low boiling point, is extensively used in protecting groups-based synthetic strategies. Indeed, synthetic compounds bearing basic functions, such as amines or guanidines (commonly found in peptido or peptidomimetic derivatives), developed in the frame of drug discovery programmes, are often isolated as trifluoroacetate (TF-Acetate) salts and their biological activity is assessed as such in in vitro, ex vivo, or in vivo experiments. However, the presence of residual amounts of TFA was reported to potentially affect the accuracy and reproducibility of a broad range of cellular assays (e. g. antimicrobial susceptibility testing, and cytotoxicity assays) limiting the further development of these derivatives. Furthermore, the impact of the counterion on biological activity, including TF-Acetate, is still controversial. Herein, we present a focused case study aiming to evaluate the activity of an antibacterial AlkylGuanidino Urea (AGU) compound obtained as TF-Acetate (1a) and hydrochloride (1b) salt forms to highlight the role of counterions in affecting the biological activity. We also prepared and tested the corresponding free base (1c). The exchange of the counterions applied to polyguanidino compounds represents an unexplored and challenging field, which required significant efforts for the successful optimization of reliable methods of preparation, also reported in this work. In the end, the biological evaluation revealed a quite similar biological profile for the salt derivatives 1a and 1b and a lower potency was found for the free base 1c.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11030-022-10505-6.

Pathogen-selective killing by guanylate-binding proteins as a molecular mechanism leading to inflammasome signaling

Inflammasomes are cytosolic signaling complexes capable of sensing microbial ligands to trigger inflammation and cell death responses. Here, we show that guanylate-binding proteins (GBPs) mediate pathogen-selective inflammasome activation. We show that mouse GBP1 and GBP3 are specifically required for inflammasome activation during infection with the cytosolic bacterium Francisella novicida. We show that the selectivity of mouse GBP1 and GBP3 derives from a region within the N-terminal domain containing charged and hydrophobic amino acids, which binds to and facilitates direct killing of F. novicida and Neisseria meningitidis, but not other bacteria or mammalian cells. This pathogen-selective recognition by this region of mouse GBP1 and GBP3 leads to pathogen membrane rupture and release of intracellular content for inflammasome sensing. Our results imply that GBPs discriminate between pathogens, confer activation of innate immunity, and provide a host-inspired roadmap for the design of synthetic antimicrobial peptides that may be of use against emerging and re-emerging pathogens.

Guanylate-binding proteins (GBP) have a function in inflammasome formation and pathogen defence. Here the authors show that these GBP proteins are able to kill certain bacteria and promote selective inflammasome activation and that this is mediated by specific GBP protein regions.

Tackling antimicrobial stewardship through synergy and antimicrobial peptides

The unrestricted use of antibiotics has led to rapid development of antibiotic resistance (AR) and renewed calls to address this serious problem. This review summarizes the most common mechanisms of antibiotic action, and in turn antibiotic resistance, as well as pathways to mitigate the harm. Focus is then turned to emerging antibiotic strategies, including antimicrobial peptides (AMPs), with a discussion of their modes of action, biochemical features, and potential challenges for their use as antibiotics. The role of synergy in antimicrobials is also examined, with a focus on the synergy of AMPs and other emerging interactions with synergistic potential.

Stability and Activity of the Antimicrobial Peptide Leg1 in Solution and on Meat and Its Optimized Generation from Chickpea Storage Protein

The antimicrobial peptide Leg1 (RIKTVTSFDLPALRFLKL) from chickpea legumin is active against spoilage bacteria, yeast, and mold. The present study tested its effectiveness under food storage conditions and examined options to obtain a food-grade agent. The minimum inhibitory concentration (MIC) of Leg1 against E. coli (62.5 µM) proved stable over seven days at 20 °C or 4 °C. It was not influenced by reduced pH (5.0 vs. 6.8), which is relevant in food such as meat. An incubation temperature of 20 °C vs. 37 °C reduced the MIC to 15.6/7.8 µM against E. coli/B. subtilis. With a minimum bactericidal concentration in meat of 125/15.6 µM against E. coli/B. subtilis, Leg1 is equivalently effective as nisin and 5000–82,000 times more active than sodium benzoate, potassium sorbate, or sodium nitrite. Replacing the counter-ion trifluoroacetate derived from peptide synthesis by the more natural alternatives acetate or chloride did not impair the activity of Leg1. As an alternative to chemical synthesis, an optimized protocol for chymotryptic hydrolysis was developed, increasing the yield from chickpea legumin by a factor of 30 compared to the standard procedure. The present results indicate that food-grade Leg1 could possibly be applicable for food preservation.

Studies of the highly potent lantibiotic peptide nisin Z in aqueous solutions of salts and biological buffer components

The lantibiotic nisin, usually used as a 2.5%w/w in NaCl and milk solids, has activity against a wide range of Gram-positive bacteria, especially food-borne pathogens, and has been used as a food preservative for decades without the development of significant resistance. It has been reported that the high purity (>95%) nisin Z form has activity against the Gram-negative speciesE. coli, which is significantly reduced in the presence of NaCl. This current study examined, by¹H NMR spectroscopy, the effects of NaCl, and a range of other salts, on the observed aqueous solution¹H NMR spectra of nisin Z in the pH 3-4 range, where nisin Z has its maximum stability. Nisin's mechanism of action involves binding to the polyoxygenated pyrophosphate moiety of lipid II, and in acidic solution the positively charged C-terminus region is reported to interact with the negative sulfate groups of SDS micelles, so the study was extended to include a number of polyoxygenated anions commonly used as buffers in many biological assays. In general, the biggest changes found were in the chemical shifts of protons in the hydrophobic N-terminus region, rather than the more polar C-terminus region. The effects seen on the addition of the salts (cations and anions) were not just an overall non-specific ionic strength effect, as different salts caused different effects, in an unpredictive manner. Similarly, the polyoxygenated anions behaved differently and not predictably, and neither the cations/anions, or polyoxygenated anions, constitute a Hofmeister or inverse Hofmeister series.

Assembly of cationic and amphiphilic β-sheet FKF tripeptide confers antibacterial activity

The race drawn against bacteria facing the evolution of antimicrobial resistance fuels research for new drugs and therapeutic strategies. FKF, a tripeptide that is cationic and amphiphilic was examined in light of its potential antimicrobial activity. Acid titration of purified peptide solution, 6% w/v (136 mM), yielded a hydrogel at pH~ 4. Cryo-TEM images of FKF revealed distinct phases formed upon increase in pH, ranging from elongated needles, uniform width fibers, sheets and tubular structures. ¹H NMR attested FKF charged states as function of pH, and CD and FTIR measurements indicated that FKF β-sheet assemblies are held by both π-π stacking and H-bonds. FKF hydrogel displayed bactericidal activity against E. coli and P. aeruginosa with a 3-log reduction in bacterial counts. The hydrogel was also found effective in reducing P. aeruginosa contamination in a skin lesion model in rats. FKF forms a unique antimicrobial peptide-hydrogel, showing neglectable effect in dissolved state, yet only when fibrillary assembled it gains functionality. STATEMENT OF SIGNIFICANCE: Ultra-short peptides are at the frontier of peptide self-assembly research. The tripeptide FKF assumes distinct assembly forms that are a function of pH, for which we have pinpointed the accompanying changes in charge. Made of natural amino acids, FKF forms a pure peptide hydrogel phase, which is intrinsically antimicrobial. We demonstrate that antimicrobial effect is only assumed by the peptide assemblies, posing self-assembly as a pre-requisite for FKF's bactericidal effect. This system provides evidence for the link between specific microscopic peptide assembled structures, macroscopic gel formation and antimicrobial effect, utilized to alleviate bacterial contamination in vivo.

Review: Lessons Learned From Clinical Trials Using Antimicrobial Peptides (AMPs)

Antimicrobial peptides (AMPs) or host defense peptides protect the host against various pathogens such as yeast, fungi, viruses and bacteria. AMPs also display immunomodulatory properties ranging from the modulation of inflammatory responses to the promotion of wound healing. More interestingly, AMPs cause cell disruption through non-specific interactions with the membrane surface of pathogens. This is most likely responsible for the low or limited emergence of bacterial resistance against many AMPs. Despite the increasing number of antibiotic-resistant bacteria and the potency of novel AMPs to combat such pathogens, only a few AMPs are in clinical use. Therefore, the current review describes (i) the potential of AMPs as alternatives to antibiotics, (ii) the challenges toward clinical implementation of AMPs and (iii) strategies to improve the success rate of AMPs in clinical trials, emphasizing the lessons we could learn from these trials.

Synthesis and Characterization of Lipophilic Salts of Metformin to Improve Its Repurposing for Cancer Therapy

Epidemiological evidence has accentuated the repurposing of metformin hydrochloride for cancer treatment. However, the extreme hydrophilicity and poor permeability of metformin hydrochloride are responsible for its poor anticancer activity in vitro and in vivo. Here, we report the synthesis and characterization of several lipophilic metformin salts containing bulky anionic permeation enhancers such as caprate, laurate, oleate, cholate, and docusate as counterions. Of various counterions tested, only docusate was able to significantly improve the lipophilicity and lipid solubility of metformin. To evaluate the impact of the association of anionic permeation enhancers with metformin, we checked the in vitro anticancer activity of various lipophilic salts of metformin using drug-sensitive (MYCN-2) and drug-resistant (SK-N-Be2c) neuroblastoma cells as model cancer cells. Metformin hydrochloride showed a very low potency (IC50 ≈ >100 mM) against MYCN-2 and SK-N-Be2c cells. Anionic permeation enhancers showed a considerably higher activity (IC50 ≈ 125 μM to 1.6 mM) against MYCN-2 and SK-N-Be2c cells than metformin. The association of metformin with most of the bulky anionic agents negatively impacted the anticancer activity against MYCN-2 and SK-N-Be2c cells. However, metformin docusate showed 700- to 4300-fold improvement in anticancer potency compared to metformin hydrochloride and four- to five-fold higher in vitro anticancer activity compared to sodium docusate, indicating a synergistic association between metformin and docusate. A similar trend was observed when we tested the in vitro activity of metformin docusate, sodium docusate, and metformin hydrochloride against hepatocellular carcinoma (HepG2) and triple-negative breast cancer (MDA-MB-231) cells.

The Antimicrobial Peptide Temporin G: Anti-Biofilm, Anti-Persister Activities, and Potentiator Effect of Tobramycin Efficacy Against Staphylococcus aureus

Bacterial biofilms are a serious threat for human health, and the Gram-positive bacterium Staphylococcus aureus is one of the microorganisms that can easily switch from a planktonic to a sessile lifestyle, providing protection from a large variety of adverse environmental conditions. Dormant non-dividing cells with low metabolic activity, named persisters, are tolerant to antibiotic treatment and are the principal cause of recalcitrant and resistant infections, including skin infections. Antimicrobial peptides (AMPs) hold promise as new anti-infective agents to treat such infections. Here for the first time, we investigated the activity of the frog-skin AMP temporin G (TG) against preformed S. aureus biofilm including persisters, as well as its efficacy in combination with tobramycin, in inhibiting S. aureus growth. TG was found to provoke ~50 to 100% reduction of biofilm viability in the concentration range from 12.5 to 100 µM vs ATCC and clinical isolates and to be active against persister cells (about 70–80% killing at 50–100 µM). Notably, sub-inhibitory concentrations of TG in combination with tobramycin were able to significantly reduce S. aureus growth, potentiating the antibiotic power. No critical cytotoxicity was detected when TG was tested in vitro up to 100 µM against human keratinocytes, confirming its safety profile for the development of a new potential anti-infective drug, especially for treatment of bacterial skin infections.

The Role of Counter-Ions in Peptides-An Overview

Peptides and proteins constitute a large group of molecules that play multiple functions in living organisms. In conjunction with their important role in biological processes and advances in chemical approaches of synthesis, the interest in peptide-based drugs is still growing. As the side chains of amino acids can be basic, acidic, or neutral, the peptide drugs often occur in the form of salts with different counter-ions. This review focuses on the role of counter-ions in peptides. To date, over 60 peptide-based drugs have been approved by the FDA. Based on their area of application, biological activity, and results of preliminary tests they are characterized by different counter-ions. Moreover, the impact of counter-ions on structure, physicochemical properties, and drug formulation is analyzed. Additionally, the application of salts as mobile phase additives in chromatographic analyses and analytical techniques is highlighted.

New Dual CK2/HDAC1 Inhibitors with Nanomolar Inhibitory Activity against Both Enzymes

Four potent CK2 inhibitors derived from CX-4945 are described. They also provided nanomolar activity against HDAC1, therefore having promising utility as dual-target agents for cancer. The linker length between the hydroxamic acid and the CX-4945 scaffold plays an important role in dictating balanced activity against the targeted enzymes. The seven-carbon linker (compound 15c) was optimal for inhibition of both CK2 and HDAC1. Remarkably, 15c showed 3.0 and 3.5 times higher inhibitory activity than the reference compounds CX-4945 (against CK2) and SAHA (against HDAC1), respectively. Compound 15c exhibited micromolar activity in cell-based cytotoxic assays against multiple cell lines.

Ultrashort Cationic Lipopeptides-Effect of N-Terminal Amino Acid and Fatty Acid Type on Antimicrobial Activity and Hemolysis

Ultrashort cationic lipopeptides (USCLs) are promising antimicrobial agents that hypothetically may be alternatively used to combat pathogens such as bacteria and fungi. In general, USCLs consist of fatty acid chains and a few basic amino acid residues. The main shortcoming of USCLs is their relatively high cytotoxicity and hemolytic activity. This study focuses on the impact of the hydrophobic fatty acid chain, on both antimicrobial and hemolytic activities. To learn more about this region, a series of USCLs with different straight-chain fatty acids (C8, C10, C12, C14) attached to the tripeptide with two arginine residues were synthesized. The amino acid at the N-terminal position was exchanged for proteinogenic and non-proteinogenic amino acid residues (24 in total). Moreover, the branched fatty acid residues were conjugated to N-terminus of a dipeptide with two arginine residues. All USCLs had C-terminal amides. USCLs were tested against reference bacterial strains (including ESKAPE group) and Candida albicans. The hemolytic potential was tested on human erythrocytes. Hydrophobicity of the compounds was evaluated by RP-HPLC. Shortening of the fatty acid chain and simultaneous addition of amino acid residue at N-terminus were expected to result in more selective and active compounds than those of the reference lipopeptides with similar lipophilicity. Hypothetically, this approach would also be beneficial to other antimicrobial peptides where N-lipidation strategy was used to improve their biological characteristics.

The Analogs of Temporin-GHa Exhibit a Broader Spectrum of Antimicrobial Activity and a Stronger Antibiofilm Potential against Staphylococcus aureus

The abuse of antibiotics has led to the emergence of multidrug-resistant bacteria, which is becoming a serious worldwide problem people have to face. In our previous study, temporin-GHa (GHa) cloned from Hylarana guentheri showed antimicrobial activity against Gram-positive bacteria. In order to improve its therapeutic potential, we used a template-based and a database-assisted design to obtain three derived peptides by replacing the histidine at both ends of GHa with lysine, which exhibited faster and stronger bactericidal activity and a broader spectrum than the parent peptide. GHaK and GHa4K targeted to the bacterial membrane to exert their antibacterial activities at a faster membrane damage rate. The derived peptides inhibited the initial adhesion and the formation of Staphylococcus aureus biofilms, and eradicated the mature biofilms, which indicated that the derived peptides effectively penetrated the biofilm and killed bacteria. The therapeutic index (TI) and cell selectivity index (CSI) of the derived peptides increased significantly, which means a broader therapeutic window of the derived peptides. The derived peptides with improved activity and cell selectivity have the potential to be the promising candidates for the treatment of S. aureus infections. Our research also provides new insights into the design and development of antimicrobial peptides.

Antimicrobial Activity of Selected Antimicrobial Peptides Against Planktonic Culture and Biofilm of Acinetobacter baumannii

Acinetobacter baumannii is one of the most challenging pathogens, on account of its predisposition to develop resistance leading to severe, difficult-to-treat infections. As these bacteria are more usually isolated from nosocomial infections, the new therapeutic options are demanded. Antimicrobial peptides (AMPs) are compounds likely to find application in the treatment of A. baumannii. These compounds exhibit a wide spectrum of antimicrobial activity and were found to be effective against biofilm. In this study, eight AMPs, namely aurein 1.2, CAMEL, citropin 1.1., LL-37, omiganan, r-omiganan, pexiganan, and temporin A, were tested for their antimicrobial activity. A reference strain of A. baumannii ATCC 19606 was used. Antimicrobial assays included determination of the minimum inhibitory concentration and the minimum biofilm eradication concentration. Considering the fact that the majority of A. baumannii infections are associated with mechanical ventilation and the use of indwelling devices, the activity against biofilm was assessed on both a polystyrene surface and tracheal tube fragments. In addition, cytotoxicity (HaCaT) was determined and in vitro selectivity index was calculated.

Rose Bengal-Mediated Photoinactivation of Multidrug Resistant Pseudomonas aeruginosa Is Enhanced in the Presence of Antimicrobial Peptides

Due to the overuse of antibiotics in medicine and food production, and their targeted mechanism of action, an increasing rate in spreading of antibiotic resistance genes has been noticed. This results in inefficient therapy outcomes and higher mortality all over the world. Pseudomonas aeruginosa (carbapenem-resistant) is considered one of the top three critical species according to the World Health Organization’s priority pathogens list. This means that new drugs and/or treatments are needed to tackle infections caused by this bacterium. In this context search for new/alternative approaches that would overcome resistance to classical antimicrobials is of prime importance. The use of antimicrobial photodynamic inactivation (aPDI) and antimicrobial peptides (AMPs) is an efficient strategy to treat localized infections caused by multidrug-resistant P. aeruginosa. In this study, we have treated P. aeruginosa cells photodynamically in the presence and in the absence of AMP (CAMEL or pexiganan). The conditions for aPDI were as follows: rose bengal (RB) as a photosensitizing agent at 1–10 μM concentration, and subsequent irradiation with 514 nm-LED at 23 mW/cm² irradiance. The analysis of cell number after the treatment has shown that the combined action of RB-mediated aPDI and cationic AMPs reduced the number of viable cells below the limit of detection (<1log₁₀ CFU/ml). This was in contrast to no reduction or partial reduction after aPDI or AMP applied separately. Students t-test was applied to test the statistical significance of the results. Noteworthy, our treatment proved to be effective against all 35 clinical isolates of P. aeruginosa tested within this study, including those characterized as multiresistant. Moreover, we demonstrated that such treatment is safe and does not violate the growth dynamics of human keratinocytes (77.3–97.64% survival depending on the concentration of the studied compounds or their mixtures).