Isolation and identification of antibacterial compounds from Thymus kotschyanus aerial parts and Dianthus caryophyllus flower buds

Aim of the studyThe aerial parts of Thymus kotschyanus Boiss. and Hohen. (Lamiaceae) and flower buds of Dianthus caryophyllus L. (Caryophyllaceae) have been traditionally implemented in the treatment of wounds, throat and gum infections and gastro-intestinal disorder by the indigenous people of northern Iraq, although the compounds responsible for the medicinal properties have not been identified. In this study, antibacterial compounds from both plants were isolated and characterized, and the biological activity of each compound was assessed individually and combined.Materials and methodsCompounds were isolated and characterized from the extracted essential oils of both plants using different spectral techniques: TLC, FTIR spectra and HPLC. The minimum inhibitory concentrations MIC values for the compounds were assessed individually and combined based on a microdilution and the checkerboard method in 96 multi-well microtiter plates.ResultsTwo known compounds were isolated from the essential oils of both plants and were identified as thymol and eugenol. The isolated compounds were investigated for their single and combined antibacterial activities against seven selected pathogenic bacteria; Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Proteus mirabilis, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. Thymol MIC values ranged from 15.6 to 250.0 μg/ml and B. cereus was found to be the most sensitive pathogen with a MIC value of 15.6 μg/ml. Eugenol achieved stronger MIC values against most tested pathogens and the best MIC value (15.6 μg/ml) was observed against B. cereus, L. monocytogenes and K. pneumoniae whereas, S. aureus, P. mirabilis and E. coli were inhibited with a MIC value of 31.2 μg/ml. Combination results had antibacterial enhancement against most pathogens and the best synergistic result was seen against P. mirabilis and E. coli.ConclusionsThe isolation of two antibacterial compounds from Thymus kotschyanus aerial parts and Dianthus caryophyllus flower buds validates the use of these species in the treatment of throat and gum infections, wound-healing and gastro-intestinal disorder.     

Inhibition and destruction of Pseudomonas aeruginosa biofilms by antibiotics and antimicrobial peptides

Pseudomonas aeruginosa is one of the major nosocomial pathogen that can causes a wide variety of acute and chronic infections P. aeruginosa is a dreaded bacteria not just because of the high intrinsic and acquired antibiotic resistance rates but also the biofilm formation and production of multiple virulence factors. We investigated the in vitro activities of antibiotics (ceftazidime, tobramycin, ciprofloxacin, doripenem, piperacillin and colistin) and antimicrobial cationic peptides (AMPs; LL-37, CAMA: cecropin(1–7)-melittin A(2–9) amide, melittin, defensin and magainin-II) alone or in combination against biofilms of laboratory strain ATCC 27853 and 4 clinical strains of P. aeruginosa. The minimum inhibitory concentrations (MIC), minimum bactericidal concentration (MBC) and minimum biofilm eradication concentrations (MBEC) were determined by microbroth dilution technique. The MBEC values of antibiotics and AMPs were 80–>5120 and 640–>640 mg/L, respectively. When combined with the LL-37 or CAMA at 1/10× MBEC, the MBEC values of antibiotics that active against biofilms, were decreased up to 8-fold. All of the antibiotics, and AMPs were able to inhibit the attachment of bacteria at the 1/10× MIC and biofilm formation at 1× or 1/10× MIC concentrations. Time killing curve studies showed 3-log₁₀ killing against biofilms in 24 h with almost all studied antibiotics and AMPs. Synergism were seen in most of the studied combinations especially CAMA/LL-37 + ciprofloxacin against at least one or two strains’ biofilms. Since biofilms are not affected the antibiotics at therapeutic concentrations, using a combination of antimicrobial agents including AMPs, or inhibition of biofilm formation by blocking the attachment of bacteria to surfaces might be alternative methods to fight with biofilm associated infections.     

Tannic acid affects the phenotype of Staphylococcus aureus resistant to tetracycline and erythromycin by inhibition of efflux pumps

The widespread use of antibiotics created selective pressure for the emergence of strains that would persist despite antibiotic toxicity. The bacterial resistance mechanisms are several, with efflux pumps being one of the main ones. These pumps are membrane proteins with the function of removing antibiotics from the cell cytoplasm. Due to this importance, the aim of this work was to evaluate the inhibitory effect of tannic acid against efflux pumps expressed by the Staphylococcus aureus RN4220 and IS-58 strains. The efflux pump inhibition was assayed using a sub-inhibitory concentration of efflux pump standard inhibitors and tannic acid (MIC/8), observing their capacity to decrease the MIC of Ethidium bromide (EtBr) and antibiotics due the possible inhibitory effect of these substances. The MICs of EtBr and antibiotics were significantly different in the presence of tannic acid, indicating the inhibitory effect of this product against efflux pumps of both strains. These results indicate the possible usage of tannic acid as an inhibitor and an adjuvant in the antibiotic therapy against multidrug resistant bacteria (MDR).     

A novel antimicrobial peptide derived from modified N-terminal domain of bovine lactoferrin: Design,synthesis, activity against multidrug-resistant bacteria and Candida

Lactoferrin (LF) is believed to contribute to the host's defense against microbial infections. This work focuses on the antibacterial and antifungal activities of a designed peptide, L10 (WFRKQLKW) by modifying the first eight N-terminal residues of bovine LF by selective homologous substitution of amino acids on the basis of hydrophobicity, L10 has shown potent antibacterial and antifungal properties against clinically isolated extended spectrum beta lactamases (ESBL), producing gram-negative bacteria as well as Candida strains with minimal inhibitory concentrations (MIC) ranging from 1 to 8 μg/mL and 6.5 μg/mL, respectively. The peptide was found to be least hemolytic at a concentration of 800 μg/mL. Interaction with lipopolysaccharide (LPS) and lipid A (LA) suggests that the peptide targets the membrane of gram-negative bacteria. The membrane interactive nature of the peptide, both antibacterial and antifungal, was further confirmed by visual observations employing electron microscopy. Further analyses, by means of propidium iodide based flow cytometry, also supported the membrane permeabilization of Candida cells. The peptide was also found to possess anti-inflammatory properties, by virtue of its ability to inhibit cyclooxygenase-2 (COX-2). L10 therefore emerges as a potential therapeutic remedial solution for infections caused by ESBL positive, gram-negative bacteria and multidrug-resistant (MDR) fungal strains, on account of its multifunctional activities. This study may open up new approach to develop and design novel antimicrobials.     

Cationic amphipathic peptides KT2 and RT2 are taken up into bacterial cells and kill planktonic and biofilm bacteria

We investigated the mechanisms of two tryptophan-rich antibacterial peptides (KT2 and RT2) obtained in a previous optimization screen for increased killing of both Gram-negative and Gram-positive bacteria pathogens. At their minimal inhibitory concentrations (MICs), these peptides completely killed cells of multidrug-resistant, enterohemorrhagic pathogen Escherichia coli O157:H7 within 1–5 min. In addition, both peptides exhibited anti-biofilm activity at sub-MIC levels. Indeed, these peptides prevented biofilm formation and triggered killing of cells in mature E. coli O157:H7 biofilms at 1 μM. Both peptides bound to bacterial surface LPS as assessed using the dansyl-polymyxin displacement assay, and were able to interact with the lipids of liposomes as determined by observing a tryptophan blue shift. Interestingly, even though these peptides were highly antimicrobial, they did not induce pore formation or aggregates in bacterial cell membranes. Instead these peptides readily penetrated into bacterial cells as determined by confocal microscopy of labeled peptides. DNA binding assays indicated that both peptides bound to DNA with higher affinity than the positive control peptide buforin II. We propose that cationic peptides KT2 and RT2 bind to negatively-charged LPS to enable self-promoted uptake and, subsequently interact with cytoplasmic membrane phospholipids through their hydrophobic domains enabling translocation across the bacterial membrane and entry into cells within minutes and binding to DNA and other cytoplasmic membrane. Due to their dual antimicrobial and anti-biofilm activities, these peptides may find use as an alternative to (or in conjunction with) conventional antibiotics to treat acute infections caused by planktonic bacteria and chronic, biofilm-related infections.     

Lemairones A and B: Two new antibacterial tetraflavonoids from the leaves of Zanthoxylum lemairei (Rutaceae)

Zanthoxylum lemairei is widely used in African folk medicine for its pharmacological relevance. Chemical investigation of the ethanol extract from the leaves of this plant lead to the isolation of two new tetraflavonoids, lemairones A (1) and B (2), along with three known compounds, lupeol, sitosterol, and sitosterol 3-O-β-d-glucopyranoside. The antibacterial screening of the leaves of this plant, characterization of compounds 1 and 2, and their antibacterial activity are reported for the first time. The isolation of the compounds was performed using different chromatographic methods while their structures were elucidated by spectroscopic techniques including MS and NMR, and by comparison of data with those of similar flavonoids reported in the literature. The isolated compounds and the crude extract were tested against ten Gram negative multi-resistance bacterial strains including clinical isolates using a broth dilution method. The crude ethanol extract showed weak activity against the tested bacteria strains with a minimal inhibitory concentration (MIC) ranging from 512 to 1024 μg/mL. Among the isolated metabolites, only the new tetraflavonoids were tested. Lemairone A displayed weak activity while lemairone B had moderate activity against the resistant Escherichia coli AG100 with MIC values of 128 μg/mL and 64 μg/mL respectively. In addition, both molecules displayed weak activity against Klebsiella pneumoniae KP55 (MIC 128 μg/mL).     

Eugenol: A Phyto-Compound Effective against Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus Clinical Strain Biofilms

Background

Inhibition and eradication of Staphylococcus aureus biofilms with conventional antibiotic is difficult, and the treatment is further complicated by the rise of antibiotic resistance among staphylococci. Consequently, there is a need for novel antimicrobials that can treat biofilm-related infections and decrease antibiotics burden. Natural compounds such as eugenol with anti-microbial properties are attractive agents that could reduce the use of conventional antibiotics. In this study we evaluated the effect of eugenol on MRSA and MSSA biofilms in vitro and bacterial colonization in vivo.

Methods and Results

Effect of eugenol on in vitro biofilm and in vivo colonization were studied using microtiter plate assay and otitis media-rat model respectively. The architecture of in vitro biofilms and in vivo colonization of bacteria was viewed with SEM. Real-time RT-PCR was used to study gene expression. Check board method was used to study the synergistic effects of eugenol and carvacrol on established biofilms. Eugenol significantly inhibited biofilms growth of MRSA and MSSA in vitro in a concentration-dependent manner. Eugenol at MIC or 2×MIC effectively eradicated the pre-established biofilms of MRSA and MSSA clinical strains. In vivo, sub-MIC of eugenol significantly decreased 88% S. aureus colonization in rat middle ear. Eugenol was observed to damage the cell-membrane and cause a leakage of the cell contents. At sub-inhibitory concentration, it decreases the expression of biofilm-and enterotoxin-related genes. Eugenol showed a synergistic effect with carvacrol on the eradication of pre-established biofilms.

Conclusion/Major Finding

This study demonstrated that eugenol exhibits notable activity against MRSA and MSSA clinical strains biofilms. Eugenol inhibited biofilm formation, disrupted the cell-to-cell connections, detached the existing biofilms, and killed the bacteria in biofilms of both MRSA and MSSA with equal effectiveness. Therefore, eugenol may be used to control or eradicate S. aureus biofilm-related infections.     

Assessment of synergistic antibacterial activity of combined biosurfactants revealed by bacterial cell envelop damage

Besides potential surface activity and some beneficial physical properties, biosurfactants express antibacterial activity. Bacterial cell membrane disrupting ability of rhamnolipid produced by Pseudomonas aeruginosa C2 and a lipopeptide type biosurfactant, BS15 produced by Bacillus stratosphericus A15 was examined against Staphylococcus aureus ATCC 25923 and Escherichia coli K8813. Broth dilution technique was followed to examine minimum inhibitory concentration (MIC) of both the biosurfactants. The combined effect of rhamnolipid and BS15 against S. aureus and E. coli showed synergistic activity by expressing fractional inhibitory concentration (FIC) index of 0.43 and 0.5. Survival curve of both the bacteria showed bactericidal activity after treating with biosurfactants at their MIC obtained from FIC index study as it killed > 90% of initial population. The lesser value of MIC than minimum bactericidal concentration (MBC) of the biosurfactants also supported their bactericidal activity against both the bacteria. Membrane permeability against both the bacteria was supported by amplifying protein release, increasing of cell surface hydrophobicity, withholding capacity of crystal violet dye and leakage of intracellular materials. Finally cell membrane disruption was confirmed by scanning electron microscopy (SEM). All these experiments expressed synergism and effective bactericidal activity of the combination of rhamnolipid and BS15 by enhancing the bacterial cell membrane permeability. Such effect of the combination of rhamnolipid and BS15 could make them promising alternatives to traditional antibiotic in near future.     

Synthesis of linear and cyclic guazatine derivatives endowed with antibacterial activity

Antibiotic resistance has reached alarming levels in many clinically-relevant human pathogens, and there is an increasing clinical need for new antibiotics active on drug-resistant Gram-negative pathogens who rapidly evolve towards pandrug resistance phenotypes. Here, we report on two related classes of guanidinic compounds endowed with antibacterial activity. The two best compounds (9a and 13d) exhibited the most potent antibacterial activity with MIC values ranging 0.12–8 μg/ml with most tested pathogens, including both Gram-positive and Gram-negative bacteria. Interestingly, MIC values were not affected (1–8 μg/ml) when measured using recent clinical isolates with various antibiotic resistance determinants. The results reported herein identify guazatine derivatives as an interesting starting point for the optimization of a potentially novel class of antibacterial agents.     

Chemical,biochemical and microbiological properties of a brominated nitrovinylfuran with broad-spectrum antibacterial activity

A di-bromo substituted nitrovinylfuran with reported broad-spectrum antibacterial activity was found to be a potent inhibitor of MurA, a key enzyme in peptidoglycan biosynthesis. Further characterization of the compound was carried out to assess its reactivity towards thiol nucleophiles, its stability and degradation under aqueous conditions, inhibitory potential at other enzymes, and antibacterial and cytotoxic activity. Our results indicate that the nitrovinylfuran derivative is reactive towards cysteine residues in proteins, as demonstrated by the irreversible inhibition of MurA and bacterial methionine aminopeptidase. Experiments with proteins and model thiols indicate that the compound forms covalent adducts with SH groups and induces intermolecular disulfide bonds, with the intermediate formation of a monobromide derivative. The parent molecule as well as most of its breakdown products are potent antibiotics with MIC values below 4 μg/mL and are active against multiresistant strains such as methicillin-resistant Staphylococcus aureus (MRSA). Further development of the bromonitrovinyl scaffold towards antibiotics with clinical relevance, however, requires optimization of the antibiotic–cytotoxic selectivity profile.     

Antibacterial activities of the methanol extracts of Albizia adianthifolia,Alchornea laxiflora,Laportea ovalifolia and three other Cameroonian plants against multi-drug resistant Gram-negative bacteria

In the last 10 years, resistance in Gram-negative bacteria has been increasing. The present study was designed to evaluate the in vitro antibacterial activities of the methanol extracts of six Cameroonian medicinal plants Albizia adianthifolia, Alchornea laxiflora, Boerhavia diffusa, Combretum hispidum, Laportea ovalifolia and Scoparia dulcis against a panel of 15 multidrug resistant Gram-negative bacterial strains. The broth microdilution was used to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the extracts. The preliminary phytochemical screening of the extracts was conducted according to the reference qualitative phytochemical methods. Results showed that all extracts contained compounds belonging to the classes of polyphenols and triterpenes, other classes of chemicals being selectively distributed. The best antibacterial activities were recorded with bark and root extracts of A. adianthifolia as well as with L. ovalifolia extract, with MIC values ranging from 64 to 1024 μg/mL on 93.3% of the fifteen tested bacteria. The lowest MIC value of 64 μg/mL was recorded with A. laxiflora bark extract against Enterobacter aerogenes EA289.Finally, the results of this study provide evidence of the antibacterial activity of the tested plants and suggest their possible use in the control of multidrug resistant phenotypes.     

The functional interaction between abaecin and pore-forming peptides indicates a general mechanism of antibacterial potentiation

Long-chain proline-rich antimicrobial peptides such as bumblebee abaecin show minimal activity against Gram-negative bacteria despite binding efficiently to specific intracellular targets. We recently reported that bumblebee abaecin interacts with Escherichia coli DnaK but shows negligible antibacterial activity unless it is combined with sublethal doses of the pore-forming peptide hymenoptaecin. These two bumblebee peptides are co-expressed in vivo in response to a bacterial challenge. Here we investigated whether abaecin interacts similarly with pore-forming peptides from other organisms by replacing hymenoptaecin with sublethal concentrations of cecropin A (0.3 μM) or stomoxyn (0.05 μM). We found that abaecin increased the membrane permeabilization effects of both peptides, confirming that it can reduce the minimal inhibitory concentrations of pore-forming peptides from other species. We also used atomic force microscopy to show that 20 μM abaecin combined with sublethal concentrations of cecropin A or stomoxyn causes profound structural changes to the bacterial cell surface. Our data indicate that the potentiating functional interaction between abaecin and pore-forming peptides is not restricted to specific co-expressed peptides from the same species but is likely to be a general mechanism. Combination therapies based on diverse insect-derived peptides could therefore be used to tackle bacteria that are recalcitrant to current antibiotics.     

Antibiotic resistance modulation by natural products obtained from Nasutitermes corniger (Motschulsky, 1855) and its nest

Insects and their products are included in the traditional pharmacopoeia of various ethnic groups worldwide. In the Brazilian semiarid region can be highlighted the use of the termite Nasutitermes corniger for the treatment of various diseases. This study evaluated the ethanol extract of N. corniger and its nest as an antimicrobial agent and as a modulator of bacterial resistance against multidrug strains. The Minimum Inhibitory Concentration (MIC) of the extract on Staphylococcus aureus and Escherichia coli by microdilution was determined, as well as MIC of antibiotics in the presence and absence of extract. Despite having no significant antimicrobial activity (MIC ⩾ 1000 μg mL⁻¹), the extract showed additive activity to the antibiotic efficacy, significantly reducing its MIC. These results suggest that N. corniger and its nest are promising natural products for use in antimicrobial therapy.     

Design,synthesis and antibacterial evaluation of honokiol derivatives

Staphylococcus aureus is a major and dangerous human pathogen that causes a range of clinical manifestations of varying severity, and is the most commonly isolated pathogen in the setting of skin and soft tissue infections, pneumonia, suppurative arthritis, endovascular infections, foreign-body associated infections, septicemia, osteomyelitis, and toxic shocksyndrome. Honokiol, a pharmacologically active natural compound derived from the bark of Magnolia officinalis, has antibacterial activity against Staphylococcus aureus which provides a great inspiration for the discovery of potential antibacterial agents. Herein, honokiol derivatives were designed, synthesized and evaluated for their antibacterial activity by determining the minimum inhibitory concentration (MIC) against S. aureus ATCC25923 and Escherichia coli ATCC25922 in vitro. 7c exhibited better antibacterial activity than other derivatives and honokiol. The structure-activity relationships indicated piperidine ring with amino group is helpful to improve antibacterial activity. Further more, 7c showed broad spectrum antibacterial efficiency against various bacterial strains including eleven gram-positive and seven gram-negative species. Time-kill kinetics against S. aureus ATCC25923 in vitro revealed that 7c displayed a concentration-dependent effect and more rapid bactericidal kinetics better than linezolid and vancomycin with the same concentration. Gram staining assays of S. aureus ATCC25923 suggested that 7c could destroy the cell walls of bacteria at 1 × MIC and 4 × MIC.     

In vitro pharmacokinetics of antimicrobial cationic peptides alone and in combination with antibiotics against methicillin resistant Staphylococcus aureus biofilms

Antibiotic therapy for methicillin-resistant Staphylococcus aureus (MRSA) infections is becoming more difficult in hospitals and communities because of strong biofilm-forming properties and multidrug resistance. Biofilm-associated MRSA is not affected by therapeutically achievable concentrations of antibiotics. Therefore, we investigated the in vitro pharmacokinetic activities of antimicrobial cationic peptides (AMPs; indolicidin, cecropin [1–7]-melittin A [2–9] amide [CAMA], and nisin), either alone or in combination with antibiotics (daptomycin, linezolid, teicoplanin, ciprofloxacin, and azithromycin), against standard and 2 clinically obtained MRSA biofilms. The minimum inhibitory concentrations (MIC) and minimum biofilm-eradication concentrations (MBEC) were determined by microbroth dilution technique. The time-kill curve (TKC) method was used to determine the bactericidal activities of the AMPs alone and in combination with the antibiotics against standard and clinically obtained MRSA biofilms. The MIC values of the AMPs and antibiotics ranged between 2 to 16 and 0.25 to 512 mg/L, and their MBEC values were 640 and 512 to 5120 mg/L, respectively. The TKC studies demonstrated that synergistic interactions occurred most frequently when using nisin + daptomycin/ciprofloxacin, indolicidin + teicoplanin, and CAMA + ciprofloxacin combinations. No antagonism was observed with any combination. AMPs appear to be good candidates for the treatment of MRSA biofilms, as they act as both enhancers of anti-biofilm activities and help to prevent or delay the emergence of resistance when used either alone or in combination with antibiotics.     

Antimicrobial activity of nisin against the swine pathogen Streptococcus suis and its synergistic interaction with antibiotics

Streptococcus suis serotype 2 is known to cause severe infections in pigs, including meningitis, endocarditis and pneumonia. Furthermore, this bacterium is considered an emerging zoonotic agent. Recently, increased antibiotic resistance in S. suis has been reported worldwide. The objective of this study was to evaluate the potential of nisin, a bacteriocin of the lantibiotic class, as an antibacterial agent against the pathogen S. suis serotype 2. In addition, the synergistic activity of nisin in combination with conventional antibiotics was assessed. Using a plate assay, the nisin-producing strain Lactococcus lactis ATCC 11454 proved to be capable of inhibiting the growth of S. suis (n = 18) belonging to either sequence type (ST)1, ST25, or ST28. In a microdilution broth assay, the minimum inhibitory concentration (MIC) of purified nisin ranged between 1.25 and 5 μg/mL while the minimum bactericidal concentration (MBC) was between 5 and 10 μg/mL toward S. suis. The use of a capsule-deficient mutant of S. suis indicated that the presence of this polysaccharidic structure has no marked impact on susceptibility to nisin. Following treatment of S. suis with nisin, transmission electron microscopy observations revealed lysis of bacteria resulting from breakdown of the cell membrane. A time-killing curve showed a rapid bactericidal activity of nisin. Lastly, synergistic effects of nisin were observed in combination with several antibiotics, including penicillin, amoxicillin, tetracycline, streptomycin and ceftiofur. This study brought clear evidence supporting the potential of nisin for the prevention and treatment of S. suis infections in pigs.     

Antimicrobial peptides containing unnatural amino acid exhibit potent bactericidal activity against ESKAPE pathogens

A series of 36 synthetic antimicrobial peptides containing unnatural amino acids were screened to determine their effectiveness to treat Enterococcus faecium, Staphylococcus aureus, Klebsiella pnemoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species (ESKAPE) pathogens, which are known to commonly infect chronic wounds. The primary amino acid sequences of these peptides incorporate either three or six dipeptide units consisting of the unnatural amino acids Tetrahydroisoquinolinecarboxylic acid (Tic) and Octahydroindolecarboxylic acid (Oic). The Tic-Oic dipeptide units are separated by SPACER amino acids with specific physicochemical properties that control how these peptides interact with bacterial cell membranes of different chemical compositions. These peptides exhibited minimum inhibitory concentrations (MIC) against these pathogens in the range from >100 to 6.25 μg/mL. The observed diversity of MIC values for these peptides against the various bacterial strains are consistent with our hypothesis that the complementarity of the physicochemical properties of the peptide and the lipid of the bacteria’s cell membrane determines the resulting antibacterial activity of the peptide.     

Bis(N-amidinohydrazones) and N-(amidino)-N′-aryl-bishydrazones: New classes of antibacterial/antifungal agents

The emergence of multidrug-resistant bacterial and fungal strains poses a threat to human health that requires the design and synthesis of new classes of antimicrobial agents. We evaluated bis(N-amidinohydrazones) and N-(amidino)-N′-aryl-bishydrazones for their antibacterial and antifungal activities against panels of Gram-positive/Gram-negative bacteria as well as fungi. We investigated their potential to develop resistance against both bacteria and fungi by a multi-step resistance-selection method, explored their potential to induce the production of reactive oxygen species, and assessed their toxicity. In summary, we found that these compounds exhibited broad-spectrum antibacterial and antifungal activities against most of the tested strains with minimum inhibitory concentration (MIC) values ranging from <0.5 to >500 μM against bacteria and 1.0 to >31.3 μg/mL against fungi; and in most cases, they exhibited either superior or similar antimicrobial activity compared to those of the standard drugs used in the clinic. We also observed minimal emergence of drug resistance to these newly synthesized compounds by bacteria and fungi even after 15 passages, and we found weak to moderate inhibition of the human Ether-à-go-go-related gene (hERG) channel with acceptable IC₅₀ values ranging from 1.12 to 3.29 μM. Overall, these studies show that bis(N-amidinohydrazones) and N-(amidino)-N′-aryl-bishydrazones are potentially promising scaffolds for the discovery of novel antibacterial and antifungal agents.     

Anti-tubercular agents. Part 8: Synthesis,antibacterial and antitubercular activity of 5-nitrofuran based 1,2,3-triazoles

A series of 5-nitrofuran–triazole conjugates were synthesized and evaluated for their antimicrobial activity against both Gram-positive and Gram-negative bacterial strains. All the compounds exhibited promising inhibition towards Gram-positive pathogenic strains, while mild inhibitory effects were observed towards Gram-negative bacterial strains. Some of the compounds 8a, 8b, 8e, 8f, 8h are most active among the series exhibiting MIC value of 1.17 μg/ml against different bacterial strains. The bactericidal activity is found to be in accordance with the bacterial growth inhibition data. Compound 8e was found to be equipotent to the standard drug Ciprofloxacin displaying MBC value of 1.17 μg/ml against the bacterial strain Bacillus subtilis. The compounds have also demonstrated promising antibacterial activity against the resistant strain MRSA and were found to be effective inhibitors of biofilm formation. The compound 8b exhibited excellent anti-biofilm activity with IC₅₀ value as low as 0.8 μg/ml. These conjugates were also screened for antitubercular activity against Mycobacterium tuberculosis H₃₇Rv strain. Compound 8e showed promising antitubercular activity with MIC value of 0.25 μg/ml. Most of these compounds are less toxic to normal mammalian cells than the widely used antibacterial drug Ciprofloxacin.     

Synthesis,antibacterial activities and molecular docking studies of peptide and Schiff bases as targeted antibiotics

A series of peptide and Schiff bases (PSB) were synthesized by reacting salicylic acid, primary diamines with salicylaldehyde or its derivatives, and 40 of which were newly reported. The inhibitory activities against Escherichia coli β-ketoacyl-acyl carrier protein synthase III (ecKAS III) were investigated in vitro and molecular docking simulation also surveyed. Top 10 PSB compounds which posses both good inhibitory activity and well binding affinities were picked out, and their antibacterial activities against Gram-negative and Gram-positive bacterial strains were tested, expecting to exploit potent antibacterial agent with broad-spectrum antibiotics activity. The results demonstrate compound N-(3-(5-bromo-2-hydroxybenzylideneamino)propyl)-2-hydroxybenzamide (2d) can be as a potential antibiotics agent, displaying minimal inhibitory concentration values in the range of 0.39–3.13 μg/mL against various bacteria.