Novel Miniature Membrane Active Lipopeptidomimetics against Planktonic and Biofilm Embedded Methicillin-Resistant Staphylococcus aureus

Synergistic Potential of α-Melanocyte Stimulating Hormone Based Analogues with Conventional Antibiotic against Planktonic, Biofilm-Embedded, and Systemic Infection Model of MRSA

The repotentiation of the existing antibiotics by exploiting the combinatorial potential of antimicrobial peptides (AMPs) with them is a promising approach to address the challenges of slow antibiotic development and rising antimicrobial resistance. In the current study, we explored the ability of lead second generation Ana-peptides viz. Ana-9 and Ana-10, derived from Alpha-Melanocyte Stimulating Hormone (α-MSH), to act synergistically with different classes of conventional antibiotics against methicillin-resistant Staphylococcus aureus (MRSA). The peptides exhibited prominent synergy with β-lactam antibiotics, namely, oxacillin, ampicillin, and cephalothin, against planktonic MRSA. Furthermore, the lead combination of Ana-9/Ana-10 with oxacillin provided synergistic activity against clinical MRSA isolates. Though the treatment of MRSA is complicated by biofilms, the lead combinations successfully inhibited biofilm formation and also demonstrated biofilm disruption potential. Encouragingly, the peptides alone and in combination were able to elicit in vivo anti-MRSA activity and reduce the bacterial load in the liver and kidney of immune-compromised mice. Importantly, the presence of Ana-peptides at sub-MIC doses slowed the resistance development against oxacillin in MRSA cells. Thus, this study highlights the synergistic activity of Ana-peptides with oxacillin advocating for the potential of Ana-peptides as an alternative therapeutic and could pave the way for the reintroduction of less potent conventional antibiotics into clinical use against MRSA infections.

A novel pyrazolone complex P-FAH-Cu-bpy induces death of Escherichia coli and Staphylococcus aureus by disrupting cell structure and blocking energy

A novel pyrazolone-based copper complex [Cu(L)(bpy)]∙CH3OH (P-FAH-Cu-bpy) was synthesized and previously characterized to have antitumor properties. This study aimed to investigate its antibacterial properties and action modes against Escherichia coli and Staphylococcus aureus. By agar diffusion assay, P-FAH-Cu-bpy showed strong antibacterial activity against E. coli and S. aureus with the diameter of inhibition zone of 10.17-12.50 mm and 11.83-14 mm, respectively. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the complex were 1.5 and 3 μM, respectively. Destroyed bacteria cells and debris were clearly observed by SEM. At 2 MIC and 4 MIC of P-FAH-Cu-bpy, 1.1683 and 1.9083 pg copper per cell was taken by E. coli, and 4.5670 and 8.5250 pg per cell by S. aureus, respectively. Multi-step resistance selection showed both bacteria were sensitive to P-FAH-Cu-bpy without induction of resistance within 30 generations. With P-FAH-Cu-bpy treatment, the release of nucleotides and proteins and alkaline phosphatase was increased, but the activity of K+-Na+-ATPase and Ca2+-Mg2+-ATPase and membrane conductivity were decreased in both pathogens. In conclusion, P-FAH-Cu-bpy induced death of both bacteria by destroying the cell membrane structure and blocking energy and exhibited strong antibacterial activity against E. coli and S. aureus without inducing microbial resistance.

Introduction of a β-leucine residue instead of leucine9 and glycine10 residues in Temporin L for improved cell selectivity, stability and activity against planktonic and biofilm of methicillin resistant S. aureus

Leucine and glycine residues, at the 9th and 10th positions of helical domain of naturally occurring antimicrobial peptide (AMP), Temporin L were substituted with an unnatural amino acid, β-leucine (homovaline) to improve its serum protease stability, haemolytic/cytotoxic properties and reduce the size to some extent. The designed analogue, L9βl-TL showed either equal or improved antimicrobial activity to TL against different microorganisms including the resistant strains. Interestingly, L9βl-TL also exhibited lower haemolytic and cytotoxic activities against human red blood cells and 3T3 cells, respectively. Moreover, L9βl-TL showed antibacterial activity in presence of 25% (v/v) human serum and showed resistance against proteolytic cleavage in presence of it that suggested the serum protease stability of the TL-analogue. L9βl-TL exhibited un-ordered secondary structures in both bacterial and mammalian membrane mimetic lipid vesicles as compared to the helical structures of TL in these environments. However, tryptophan fluorescence studies demonstrated more selective interaction of L9βl-TL with bacterial membrane mimetic lipid vesicles in comparison to non-selective interactions of TL with both kinds of lipid vesicles. Membrane depolarization studies with live MRSA and bacterial membrane-mimetic lipid vesicles suggested a membrane-disrupting mode of action of L9βl-TL. L9βl-TL showed faster bactericidal mechanism compared to TL against MRSA. Interestingly, L9βl-TL was found as more potent than TL either in inhibiting biofilm formation or in eradicating the mature biofilm formed by MRSA. Overall, the present work demonstrates a simple and useful strategy to design of an analogue of TL, with minimal modifications while maintaining its antimicrobial activity with lesser toxicity and higher stability which could be attempted for other AMPs as well.

The Emerging Role of Probiotics and their Derivatives against Biofilm-Producing MRSA: A Scoping Review

Background

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the main bacterial pathogens causing chronic infections, mainly because of its capacity to produce biofilm. Biofilm production is one of the underlying strategies for antibacterial drug resistance. Accordingly, preventing and attenuating biofilm production has become an emerging approach to controlling persistent infections. Therefore, this scoping review is aimed at surveying the published literature describing the usage of probiotics and their derivatives against biofilm-producing MRSA.

Methods

Updated literature searches were conducted across seven electronic databases including Web of Science, PubMed, Scopus, Cochrane Library, ProQuest, Embase, and Google Scholar to identify all original published articles about probiotics against MRSA. In this regard, studies were summarized and analyzed in the present review.

Results

In the reviewed studies, various microorganisms and compounds were used as probiotics as follows: Lactobacillus species (8 studies), Enterococcus species (4 studies), Bacillus species (2 studies), Streptomyces species (2 studies), Saccharomyces cerevisiae (1 study), Corynebacterium accolens (1 study), and Lactococcus lactis derived Nisin (3 studies). Based on our comprehensive search, 21 studies with eligibility criteria were included in the present review including 12 studies on clinical strains, 6 studies on ATCC, 2 studies simultaneously on clinical and standard strains, and finally 1 study on food sample.

Conclusions

Our study showed that there was an increasing trend in the number of publications reporting probiotics against biofilm-producing MRSA. The results of this scoping review could use to guide the undertaking of the subsequent systematic reviews. In summary, probiotics with antimicrobial and antibiofilm properties can use as an embedded agent in food products or as a biopharmaceutical in the prevention and treatment of MRSA infections.

Efficacy and Toxicity Studies of Novel α-MSH Analogues with Antibiofilm Action and β-Lactam Resensitization Potential against MRSA

Methicillin-resistant Staphylococcus aureus (MRSA), a biofilm-forming recalcitrant pathogen with a multidrug-resistant profile, poses a pandemic threat to human health and is the leading cause of severe infections in both healthcare and community settings. In this study, toward designing novel α-MSH-based peptides with enhanced activity and stability against MRSA, particularly its stationary phase and biofilm, we explored a design approach to augment the hydrophobicity of an 8-mer C-terminal α-MSH(6-13)-based peptide Ana-5 through the incorporation of a bulky unnatural amino acid. The designed Ana-peptides overcame the limitation of diminished activity in biological media and exhibited enhanced antistaphylococcal activity and cell selectivity. With membrane rupture as the primary mode of action, the peptides exhibited inhibitory potential against S. aureus biofilms. Importantly, the peptides did not exhibit any adverse effects in the in vivo toxicity studies and were also able to significantly alleviate bacterial infection in a systemic infection mice model study. Additionally, the peptides retained their activity in the presence of serum and displayed a low propensity toward resistance development in MRSA cells. Moreover, the observed synergistic potential of Ana-10 with conventional antibiotics could be vital in resurrecting discarded antibiotics. Thus, this study provides us with an exciting lead, Ana-10, for further development against biofilm-based chronic S. aureus infections.

Mitigating the toxicity of palmitoylated analogue of α-melanocyte stimulating hormone(11-13) by conjugation with gold nanoparticle: characterisation and antibacterial efficacy against methicillin sensitive and resistant Staphylococccus aureus

In an attempt to develop potent and non-toxic antimicrobial agent, the palmitoylated analogue of α-melanocyte stimulating hormone(11-13), Pal-α-MSH(11-13) was conjugated with gold nanoparticles (GNPs) for the first time and the efficacy of derived complex was investigated against two strains of Staphylococccus aureus. The GNPs were synthesized using tri-sodium citrate as reductant and Pal-α-MSH(11-13) was conjugated thereafter. The particles were characterised by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, fourier transform infrared spectroscopy etc. Conjugation occurred via electrostatic interaction between anionic GNPs and cationic Pal-α-MSH(11-13). The zeta potential of GNP-Pal-α-MSH(11-13) was - 26.91, indicating its stability. The antibacterial activity was determined by minimal inhibitory concentration (MIC) and killing kinetics assay, whereas, inhibition of biofilm formation was studied by determining the biofilm biomass by crystal violet dye binding method, viability of biofilm-embedded cells by counting CFUs and metabolic activity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The toxicity was analysed by hemolysis assay against murine RBCs and cytotoxicity against 3T3 fibroblasts. The MIC was 18 µM for GNP-Pal-α-MSH(11-13) and 12 µM for Pal-α-MSH(11-13). The killing kinetics and biofilm inhibition studies indicated the comparable efficacy of peptide before and after nano-conjugation. Importantly, the conjugation resulted in diminished toxicity, as evidenced by 0.29 ± 0.03% hemolysis and 100% viable fibroblasts at 72 µM compared to the Pal-α-MSH(11-13), showing 74.99 ± 1.59% hemolysis and 59.39 ± 1.06% viable fibroblasts. The nano-fabrication drastically reduced the peptide toxicity without compromising its antibacterial efficacy. The anionicity of the conjugate may be responsible for non-toxicity that makes them suitable for pharmaceutical applications.

Isoquinoline Antimicrobial Agent: Activity against Intracellular Bacteria and Effect on Global Bacterial Proteome

A new class of alkynyl isoquinoline antibacterial compounds, synthesized via Sonogashira coupling, with strong bactericidal activity against a plethora of Gram-positive bacteria including methicillin- and vancomycin-resistant Staphylococcus aureus (S. aureus) strains is presented. HSN584 and HSN739, representative compounds in this class, reduce methicillin-resistant S. aureus (MRSA) load in macrophages, whilst vancomycin, a drug of choice for MRSA infections, was unable to clear intracellular MRSA. Additionally, both HSN584 and HSN739 exhibited a low propensity to develop resistance. We utilized comparative global proteomics and macromolecule biosynthesis assays to gain insight into the alkynyl isoquinoline mechanism of action. Our preliminary data show that HSN584 perturb S. aureus cell wall and nucleic acid biosynthesis. The alkynyl isoquinoline moiety is a new scaffold for the development of potent antibacterial agents against fatal multidrug-resistant Gram-positive bacteria.

The multifaceted nature of antimicrobial peptides: current synthetic chemistry approaches and future directions

Bacterial infections caused by 'superbugs' are increasing globally, and conventional antibiotics are becoming less effective against these bacteria, such that we risk entering a post-antibiotic era. In recent years, antimicrobial peptides (AMPs) have gained significant attention for their clinical potential as a new class of antibiotics to combat antimicrobial resistance. In this review, we discuss several facets of AMPs including their diversity, physicochemical properties, mechanisms of action, and effects of environmental factors on these features. This review outlines various chemical synthetic strategies that have been applied to develop novel AMPs, including chemical modifications of existing peptides, semi-synthesis, and computer-aided design. We will also highlight novel AMP structures, including hybrids, antimicrobial dendrimers and polypeptides, peptidomimetics, and AMP-drug conjugates and consider recent developments in their chemical synthesis.

Enhanced efficacy of a Cu2+ complex of curcumin against Gram-positive and Gram-negative bacteria: Attributes of complex formation

Curcumin is a tantalizing molecule with multifaceted therapeutic potentials. However, its therapeutic applications are severely hampered because of poor bioavailability, attributed to its instability and aqueous insolubility. In an attempt to overcome this inherent limitation and develop curcumin-based antibacterials, we had earlier synthesized and characterized a metal complex of Cu(II) with curcumin, having the formula [Cu(Curcumin)(OCOCH₃)(H₂O)], hereafter referred to as Cu(Cur). In this study, the complex, i.e., Cu(Cur), was investigated for its stability and antibacterial activity along with its possible mechanism of action in comparison to the parent molecule, curcumin. Complex formation resulted in improved stability as Cu(Cur) was found to be highly stable under different physiological conditions. Such improved stability was verified with the help of UV-Vis spectroscopy and HPLC. With improved stability, Cu(Cur) exhibited potent and significantly enhanced activity over curcumin against both E. coli and S. aureus. Calcein leakage assay revealed that the complex triggered immediate membrane permeabilization in S. aureus. This membrane disruptive mode of action was further corroborated by microscopic visualization. The excellent potency of the complex was augmented by its safe toxicological profile as it was non-hemolytic and non-cytotoxic towards mammalian cells, making it a suitable candidate for in vivo investigations. Altogether, this investigation is a critical appraisal that advocates the antibacterial potential of this stable, membrane-targeting and non-toxic complex, thereby presenting new perspectives for its therapeutic application against bacterial infections.

Liposome encapsulated surfactant abetted copper nanoparticles alleviates biofilm mediated virulence in pathogenic Pseudomonas aeruginosa and MRSA

In the present study lipopeptide biosurfactant with high emulsification capacity produced by human skin bacterium Paenibacillus thiaminolyticus was purified and subjected to FTIR and NMR spectral analysis which gave evidence of the active characteristics of the surfactant. To augment the antivirulent potential further, the mixer of copper and copper oxide nanoparticles (CuNPs) was synthesized, and characterized by UV–Visible spectroscopy, SEM-EDAX, TEM, and Zeta analysis. Here, we attempted to enhance the antimicrobial and antibiofilm activity with the assistance of encapsulated preparation of lipopeptide and CuNPs in multilamellar liposomes. The proposed mechanism of action of lipopeptide and CuNPs liposomal preparation negatively influences the cell metabolism, secreted virulence such as staphyloxanthin, pyocyanin, and extracellular polysaccharides. The significant decline in the growth of MRSA and P. aeruginosa in both planktonic form and biofilm by lipopeptide and CuNPs treatment were visualized using scanning electron microscopy and High content screening imaging system. In vivo studies revealed that treatment with lipopeptide and CuNPs in multilamellar liposomes extended the lifespan of infected Caenorhabditis elegans by about 75%. Therefore, this study typifies lipopeptide and CuNPs could credibly be a substantial substitute over conventional antibiotics in averting the biofilm associated pathogenesis of MRSA and P. aeruginosa.

Lipidated Short Analogue of α-Melanocyte Stimulating Hormone Exerts Bactericidal Activity against the Stationary Phase of Methicillin-Resistant Staphylococcus aureus and Inhibits Biofilm Formation

Stationary phase Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), has been widely associated with many persistent infections as well as biofilm-associated infections, which are challenging due to their increasing antibiotic resistance. α-Melanocyte stimulating hormone (α-MSH) is an antimicrobial peptide (AMP) with well-established potent activity against S. aureus , but little is known about its antimicrobial efficacy against the stationary phase of the bacteria. We investigated the in vitro activities of two palmitoylated analogues, Pal-α-MSH(6-13) and Pal-α-MSH(11-13), of the C-terminal fragments of α-MSH against biofilm-producing strains of methicillin-sensitive S. aureus (MSSA) and MRSA. While both the peptides demonstrated anti-staphylococcal efficacy, Pal-α-MSH(11-13) emerged as the most effective AMP as palmitoylation led to a remarkable enhancement in its activity against stationary phase bacteria. Similar to α-MSH, both the designed analogues were membrane-active and exhibited improved bacterial membrane depolarization and permeabilization, as further confirmed via electron microscopy studies. Of the two peptides, Pal-α-MSH(11-13) was able to retain its activity in the presence of standard microbiological media, which otherwise is a major limiting factor toward the therapeutic use of α-MSH-based peptides. More importantly, Pal-α-MSH(11-13) was also highly effective in inhibiting the formation of biofilms. Furthermore, it did not lead to resistance development in MRSA cells even upon 18 serial passages at sub-MIC concentrations. These observations support the potential use of Pal-α-MSH(11-13) in the treatment of planktonic as well as sessile S. aureus infections.

Multitargeting Antibacterial Activity of a Synthesized Mn2+ Complex of Curcumin on Gram-Positive and Gram-Negative Bacterial Strains

Curcumin is an important molecule with a plethora of pharmacological activities and therapeutic potentials. Despite its efficacy, it remained a potential drug candidate owing to hydrolytic instability and poor aqueous solubility. To overcome the limitations related to low solubility, low bioavailability, and the fact that curcumin is never present in solution as a "single unit", its complex was prepared with MnII with the idea that binding to a metal ion might help to resolve these issues. The complex was characterized by elemental and spectral analysis. The structure of the complex was determined by density functional theory calculations. The complex was stable at physiological buffer conditions, unlike curcumin. It did not have any detrimental effect on mammalian cells. There was a significant enhancement in the antibacterial activity of the complex compared to curcumin against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. It showed a strong affinity for deoxyribonucleic acid (DNA) evident from a high binding constant value with calf thymus DNA and also from the retarded electrophoretic mobility of bacterial plasmid DNA. The complex showed "superoxide dismutase-like" activity leading to the generation of reactive oxygen species (ROS). The complex caused bacterial membrane perturbation evident from calcein leakage assay, which was further corroborated by scanning and transmission electron microscopic experiments. Overall, the present study shows improved stability and antibacterial potency of a nontoxic complex over curcumin. Its multitargeting mode of action such as ROS-production, effective binding with DNA, and permeabilization of bacterial membrane together allows it to be an effective antibacterial agent that could be taken further for therapeutic use against bacterial infections.

Synergistic action of substituted indole derivatives and clinically used antibiotics against drug-resistant bacteria

Aim: The current report describes the discovery of indole derivatives that synergize with standard antibiotics. Materials & methods: The antibacterial activities were determined using an optimized time-kill method, while viability of mammalian cells was assessed using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Results: The synergy is observed with methicillin- and vancomycin-resistant Staphylococcus aureus bacterial strains, against which the standard antibiotics show no activities of their own. Our indole derivatives in combination with antibiotics lack toxicity toward mammalian cells, do not promote the evolution of resistance of S. aureus in comparison to clinically established antibiotics, and likely work by permeabilizing bacterial cell membranes. Conclusion: The above-mentioned findings demonstrate the potential clinical applications of our indole derivatives.

Synthesis of novel monocarbonyl curcuminoids, evaluation of their efficacy against MRSA, including ex vivo infection model and their mechanistic studies

In continuation of our effort to improve the physiological stability and the antibacterial activity of curcuminoids against drug-resistant bacteria, a series of novel monocarbonyl curcuminoids were synthesized and screened for antibacterial activity against S. aureus and E. coli strains. These curcuminoids showed potent antibacterial activity against both methicillin-sensitive and methicillin-resistant strains of S. aureus with MIC values 2-8 and 4-16 μg/mL, respectively. They also exhibited moderate potency against E. coli strains. The four most active curcuminoids (7d, 7i, 7m, and 7p) were on further investigation found to be very stable under physiological conditions, non-hemolytic, and non-toxic toward mammalian cells up to 150 μg/mL concentration. Mechanistic studies revealed that these curcuminoids displayed potent bactericidal activity by targeting cell membranes. Further, in an ex vivo mammalian co-culture infection model study, remarkably, the curcuminoids 7i and 7p were able to clear the internalized bacteria in mammalian cells and the activity was found to be superior to conventional antibiotics such as vancomycin and linezolid. Therefore, the present study affords us water-soluble, stable, non-toxic curcuminoids that may serve as lead molecules for development as antibacterial agents against MRSA infections.

Characteristic profiles of biofilm, enterotoxins and virulence of Staphylococcus aureus isolates from dairy cows in Xinjiang Province, China

As an important zoonotic pathogen, Staphylococcus aureus has led to serious mastitis and endometritis in infected dairy cows. In this study, a total of 164 strains of S. aureus were isolated from dairy cows in Xinjiang Province, China, and subjected to assays to determine drug susceptibility and biofilm (BF) formation ability. Enterotoxin-related genes were detected, and the transcription levels of genes related to BF formation were determined by using reverse transcription-quantitative polymerase chain reaction. Moreover, the pathogenicity of isolates with different BF formation abilities was determined by measuring their hemolysis activity, half lethal dose (LD₅₀) and organ bacterial load. The results showed that 86.0% of S. aureus isolates could form BF. Among them, 42.1% of the strains had weak BF formation ability, and most strains with a strong BF formation ability were ica gene carriers. The S. aureus isolates displayed multidrug resistance and their drug resistance was positively correlated with their BF formation ability. Moreover, 96.3% of the S. aureus isolates carried enterotoxin genes. Among them, the detection rates of the novel enterotoxin genes were higher than those of conventional enterotoxin genes. Furthermore, isolates with a strong BF formation ability had higher LD50 but lower hemolysis ability and organ bacterial load than those of the isolates with weak or no BF ability. However, isolates without BF ability produced more severe pathological changes than those of isolates with strong BF formation ability. These findings suggest that higher BF ability and presence of novel enterotoxin genes are important characteristics of S. aureus isolates from dairy cows in Xinjiang Province, China, and such isolates may pose potential threats to food safety.

In Vitro and Ex Vivo Efficacy of Novel Trp-Arg Rich Analogue of α-MSH against Staphylococcus aureus

Antimicrobial peptides (AMPs), an essential component of innate immunity, are very important resources for human therapeutics to counter the current threat of drug resistance. We have previously established that one such AMP, α-melanocyte stimulating hormone (α-MSH), an endogenous neuropeptide, and its derivatives have potent antimicrobial activity against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). However, the immense potential of α-MSH for therapeutic development against staphylococcal infections is marred by its reduced efficacy in the presence of standard microbiological culture medium. To overcome this issue, in this study, we designed a series of five novel analogues of the C-terminal fragment of α-MSH, i.e., α-MSH(6-13), by replacing uncharged and less hydrophobic residues with tryptophan and arginine to increase the hydrophobicity and cationic charge of the peptide, respectively. While all of the peptides showed a preferential interaction with negatively charged phospholipid vesicles, the most hydrophobic and cationic peptide, i.e., Ana-5, exhibited the highest activity against S. aureus cells while maintaining cell selectivity. Moreover, Ana-5 could retain its activity even in complex media like the Mueller Hinton broth and displayed rapid bactericidal activity in the presence of serum. Ana-5 also caused rapid bacterial membrane depolarization, permeabilization, and cell lysis and was able to bind to polyanionic plasmid DNA suggesting a possible dual mode of action of the peptide. Importantly, Ana-5 was able to eradicate intracellular S. aureus in fibroblast cells similar to conventional antibiotics. Collectively, in the present study, we obtained a potent α-MSH-based analogue with excellent staphylocidal potency in microbial growth medium and ex vivo efficacy, which may translate into therapeutic application.

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.

Amphiphilic Triazine Polymer Derivatives as Antibacterial And Anti-atopic Agents in Mice Model

Considering the emergence of bacterial resistance and low proteolytic stability of antimicrobial peptides (AMPs), herein we developed a series of ultra-short triazine based amphipathic polymers (TZP) that are connected with ethylene diamine linkers instead of protease sensitive amide bond. The most potent oligomers, TZP3 and TZP5 not only displayed potent antibacterial action on various drug-resistant pathogens but also exhibited a strong synergic antibacterial activity in combination with chloramphenicol against multidrug-resistant Pseudomonas aeruginosa (MDRPA). Since most of atopic dermatitis (AD) infections are caused by bacterial colonization, we evaluated the potency of TZP3 and TZP5 on AD in vitro and in vivo. In vitro AD analysis of these two polymers showed significant inhibition against the release of β-hexosaminidase and tumor necrosis factor (TNF-α) from RBL-2H3 cells. In AD-like skin lesions in BALB/c mice model, these two polymers displayed significant potency in suppressing dermal and epidermal thickness, mast cell infiltration and pro-inflammatory cytokines expression. Moreover, these polymers exhibited remarkable efficacy over the allergies caused by the imbalance of Th1/Th2 by regulating total IgE and IgG2a. Finally, the impact of treatment effects of these polymers was examined through analyzing the weights and sizes of spleen and lymph node of AD-induced mice.

Effects of stigmata maydis on the methicillin resistantStaphylococus aureusbiofilm formation

Background

Mastitis is an inflammatory reaction of the mammary gland tissue, which causes huge losses to dairy farms throughout the world. Staphylococcus aureus is the most frequent agent associated with this disease. Staphylococcus aureus isolates, which have the ability to form biofilms, usually lead to chronic mastitis in dairy cows. Moreover, methicillin resistance of the bacteria further complicates the treatment of this disease. Stigmata maydis (corn silk), a traditional Chinese medicine, possess many biological activities.

Methods

In this study, we performed antibacterial activity assays, biofilm formation assays and real-time reverse transcription PCR experiments to investigate the effect of stigmata maydis (corn silk) on biofilm formation and vancomycin susceptibility of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from dairy cows with mastitis.

Results

In this study, the aqueous extracts of stigmata maydis inhibited the biofilm formation ability of MRSA strains and increased the vancomycin susceptibility of the strains under biofilm-cultured conditions.

Conclusion

This study proves that the aqueous extracts of stigmata maydis inhibit the biofilm formation ability of MRSA strains and increase the vancomycin susceptibility of the MRSA strains under biofilm-cultured conditions.