Identification of N‐Arylated NH125 Analogues as Rapid Eradicating Agents against MRSA Persister Cells and Potent Biofilm Killers of Gram‐Positive Pathogens

Bacterial biofilms housing dormant persister cells are innately tolerant to antibiotics and disinfectants, yet several membrane‐active agents are known to eradicate tolerant bacterial cells. NH125, a membrane‐active persister killer and starting point for development, led to the identification of two N‐arylated analogues ( 1 and 2 ) that displayed improved biofilm eradication potencies compared to the parent compound and rapid persister‐cell‐killing activities in stationary cultures of methicillin‐resistant Staphylococcus aureus (MRSA). We found 1 and 2 to be superior to other membrane‐active agents in biofilm eradication assays, with 1 demonstrating minimum biofilm eradication concentrations (MBEC) of 23.5, 11.7, and 2.35 μm against MRSA, methicillin‐resistant Staphylococcus epidermidis (MRSE), and vancomycin‐resistant Enterococcus faecium (VRE) biofilms, respectively. We tested our panel of membrane‐active agents against MRSA stationary cultures and found 1 to rapidly eradicate MRSA stationary cells by 4 log units (99.99 %) in 30 min. The potent biofilm eradication and rapid persister‐cell‐killing activities exhibited by N‐arylated NH125 analogues could have significant impact in addressing biofilm‐associated problems.     

Identification of a novel protein synthesis inhibitor active against gram-positive bacteria

In an effort to identify novel antibacterial chemotypes, we performed a whole‐cell screen for inhibitors of Staphylococcus aureus growth and pursued those compounds with previously uncharacterized antibacterial activity. This process resulted in the identification of a benzothiazolium salt, ABTZ‐1, that displayed potent antibacterial activity against Gram‐positive pathogens. Several clinically desirable qualities were demonstrated for ABTZ‐1 including potent activity against multidrug‐resistant clinical isolates of methicillin‐resistant S. aureus (MRSA) and vancomycin‐resistant enterococci (VRE), retention of this activity in human serum, and low hemolytic activity. The antibacterial activity of ABTZ‐1 was attributed to its inhibition of bacterial translation, as this compound prevented the incorporation of [³⁵S]methionine into S. aureus proteins, and ABTZ‐1‐resistant strains were cross‐resistant to known inhibitors of bacterial translation. ABTZ‐1 represents a promising new class of antibacterial agents.     

Chemical Synthesis and Biological Screening of 2‐Aminoimidazole‐Based Bacterial and Fungal Antibiofilm Agents

A collection of 2‐aminoimidazole/triazole amides has been synthesized and screened for antibiofilm activity. This class of small molecules was found to modulate the biofilm activity of Pseudomonas aeruginosa, a multidrug‐resistant strain of Acinetobacter baumannii (MDRAB), a methicillin‐resistant Staphylococcus aureus strain (MRSA), Escherichia coli, Rhodospirillum salexigens, Staphylococcus epidermidis, Vibrio vulnificus, and vancomycin‐resistant Enterococcus faecium as well as the yeast Candida albicans and Cryptococcus neoformans. Furthermore, lead compounds were found to not lyse red blood cells at active concentrations.     

A comparative study of the bactericidal effect of photocatalytic oxidation by TiO2 on antibiotic‐resistant and antibiotic‐sensitive bacteria

BACKGROUND: In recent decades, the increase in antibiotic‐resistant bacteria has become one of the most significant problems in public health. Titanium dioxide (TiO₂) has the potential to inactivate antibiotic‐resistant bacteria. RESULTS: In this study, TiO₂ that had been activated by ultraviolet A (UV‐A) irradiation was used to inactivate the following three antibiotic‐resistant bacteria in suspension: methicillin‐resistant Staphylococcus aureus (MRSA), multidrug‐resistant Acinetobacter baumannii (MDRAB) and vancomycin‐resistant Enterococcus faecalis (VRE). For comparison, the following antibiotic‐sensitive strains were used as controls: S. aureus (MSSA), A. baumannii (MDSAB), E. faecalis (VSE), Escherichia coli and the bacteriophage MS2. Results demonstrated that MSSA and MRSA were equally susceptible to TiO₂ photocatalysis, and the susceptibility of MDRAB was double that of MDSAB (P < 0.05). The susceptibility of VSE was 2.4 times that of VRE (P < 0.05). The results obtained from multiple regression analysis indicated that TiO₂ reaction time had the greatest influence on microbial survival following TiO₂ exposure in the presence of UV‐A. CONCLUSION: The development of antibiotic resistance does not appear to be correlated to increased resistance to TiO₂ photocatalysis, but TiO₂ in the presence of UV‐A still effectively reduces the number of antibiotic‐resistant microbes in suspension by 1–3 logs. Copyright © 2010 Society of Chemical Industry     

Antibacterial and biodegradable properties of polyhydroxyalkanoates grafted with chitosan and chitooligosaccharides via ozone treatment

Acrylic acid was grafted to ozone‐treated poly(3‐hydroxybutyric acid) (PHB) and poly(3‐hydroxybutyric acid‐co‐3‐hydroxyvaleric acid) (PHBV) membranes. The resulting membranes were further grafted with chitosan (CS) or chitooligosaccharide (COS) via esterification. These CS‐ or COS‐grafted membranes showed antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, methicilin‐resistant Staphylococcus aureus (MRSA), and S. aureus. The antibacterial activity to E. coli was the highest, whereas the antibacterial activity to MRSA was the lowest among these four bacteria tested. Acrylic acid grafting can increase the biodegradability with Alcaligens faecalis, whereas CS and COS grafting can reduce the biodegradability. In addition, CS‐grafted PHBV membrane showed higher antibacterial activity and lower biodegradability than COS‐grafted PHBV membrane. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2797–2803, 2003     

Structural Studies on 4,5‐Disubstituted 2‐Aminoimidazole‐Based Biofilm Modulators that Suppress Bacterial Resistance to β‐Lactams

A library of 4,5‐disubstituted 2‐aminoimidazole triazole amide (2‐AITA) conjugates has been successfully assembled. Upon biological screening, this class of small molecules was discovered as enhanced biofilm regulators through non‐microbicidal mechanisms against methicillin‐resistant Staphylococcus aureus (MRSA) and multidrug‐resistant Acinetobacter baumannii (MDRAB), with active concentrations in the low micromolar range. The library was also subjected to synergism and resensitization studies with β‐lactam antibiotics against MRSA. Lead compounds were identified that suppress the antibiotic resistance of MRSA by working synergistically with oxacillin, a β‐lactam antibiotic resistant to penicillinase. A further structure–activity relationship (SAR) study on the parent 2‐AITA compound delivered a 2‐aminoimidazole diamide (2‐AIDA) conjugate with significantly increased synergistic activity with oxacillin against MRSA, decreasing the MIC value of the β‐lactam antibiotic by 64‐fold. Increased anti‐biofilm activity did not necessarily lead to increased suppression of antibiotic resistance, which indicates that biofilm inhibition and resensitization are most likely occurring via distinct mechanisms.     

A Phytochemical–Halogenated Quinoline Combination Therapy Strategy for the Treatment of Pathogenic Bacteria

With the continued rise of drug‐resistant bacterial infections coupled with the current discouraging state of the antibiotic pipeline, the need for new antibacterial agents that operate through unique mechanisms compared with conventional antibiotics and work in synergy with other agents is at an all‐time high. We have discovered that gallic acid, a plant‐derived phytochemical, dramatically potentiates the antibacterial activities of several halogenated quinolines (up to 11 800‐fold potentiation against Staphylococcus aureus) against pathogenic bacteria, including drug‐resistant clinical isolates. S. aureus demonstrated the highest sensitivity towards gallic acid–halogenated quinoline combinations, including one halogenated quinoline that demonstrated potentiation of biofilm eradication activity against a methicillin‐resistant S. aureus (MRSA) clinical isolate. During our studies, we also demonstrated that these halogenated quionlines operate through an interesting metal(II) cation‐dependent mechanism and display promising mammalian cytotoxicity.     

Bis‐Cyclic Guanidines as a Novel Class of Compounds Potent against Clostridium difficile

Clostridium difficile infection (CDI) symptoms range from diarrhea to severe toxic megacolon and even death. Due to its rapid acquisition of resistance, C. difficile is listed as an urgent antibiotic‐resistant threat, and has surpassed methicillin‐resistant Staphylococcus aureus (MRSA) as the most common hospital‐acquired infection in the USA. To combat this pathogen, a new structural class of pseudo‐peptides that exhibit antimicrobial activities could play an important role. Herein we report a set of bis‐cyclic guanidine compounds that show potent antibacterial activity against C. difficile with decent selectivity. Eight compounds showed high in vitro potency against C. difficile UK6 with MIC values of 1.0 μg mL^?1, and cytotoxic selectivity index (SI) values up to 37. Moreover, the most selective compound is also effective in the treatment of C. difficile‐induced disease in a mouse model of CDI, and appears to be a very promising new candidate for the treatment of CDI.     

Design and Synthesis of Pyrophosphate‐Targeting Vancomycin Derivatives for Combating Vancomycin‐Resistant Enterococci

As the last resort for intractable Gram‐positive bacterial infections, vancomycin is losing efficacy with the emergence of vancomycin‐resistant bacteria, especially vancomycin‐resistant Enterococci (VRE). To combat this threat, we rationally designed and synthesized 39 novel vancomycin derivatives by respective or combined modifications using metal‐chelating, lipophilic, and galactose‐attachment strategies for extensive structure–activity relationship (SAR) analysis. In a proposed mechanism, the conjugation of dipicolylamine on the seventh amino acid resorcinol position or C‐terminus endowed the vancomycin backbone with binding capacity for the pyrophosphate moiety in lipid II while maintaining the intrinsic binding affinity for the dipeptide terminus of the bacterial cell wall peptidoglycan precursor. The in vitro antibacterial activities were evaluated, and the optimal compounds indicated 16‐ to 1024‐fold higher activity against VRE than that of vancomycin. Compound 11 b (3′,5′‐bis(dipicolylaminomethyl)tyrosine [1,2,3]triazolylmethoxylethyoxyl ethylaminomethyl‐N‐decylvancomycin) was found to have particularly potent activity against VRE through synergistic effects brought about by combining two peripheral modifications.     

Synthesis and Evaluation of N‐Phenylpyrrolamides as DNA Gyrase B Inhibitors

ATP‐competitive inhibitors of DNA gyrase and topoisomerase IV are among the most interesting classes of antibacterial drugs that are unrepresented in the antibacterial pipeline. We developed 32 new N‐phenylpyrrolamides and evaluated them against DNA gyrase and topoisomerase IV from E. coli and Staphylococcus aureus. Antibacterial activities were studied against Gram‐positive and Gram‐negative bacterial strains. The most potent compound displayed an IC₅₀ of 47 nm against E. coli DNA gyrase, and a minimum inhibitory concentration (MIC) of 12.5 μm against the Gram‐positive Enterococcus faecalis. Some compounds displayed good antibacterial activities against an efflux‐pump‐deficient E. coli strain (MIC=6.25 μm ) and against wild‐type E. coli in the presence of efflux pump inhibitor PAβN (MIC=3.13 μm ). Here we describe new findings regarding the structure–activity relationships of N‐phenylpyrrolamide DNA gyrase B inhibitors and investigate the factors that are important for the antibacterial activity of this class of compounds.     

Indole‐based polymer and its silver nanocomposite as advanced antibacterial agents: synthetic path,kinetics of polymerization and applications

Atom transfer radical polymerization of 1‐allylindole‐3‐carbaldehyde (AIC) was studied by employing 2‐bromoisobutyryl bromide as initiator in toluene. It led to controlled radical polymerization of AIC, with an increase of molecular weight along with the conversion of the monomer, and a relatively narrow molar mass distribution was obtained, as determined by gel permeation chromatography. The living nature of poly(1‐allylindole‐3‐carbaldehyde) (PAIC) was confirmed by the chain extension polymerization whereas ¹H NMR analysis showed that the major population of PAIC retained the chain‐end functional group. PAIC and its silver nanocomposite were found to be biologically active against some tested bacterial pathogens. Minimum inhibitory concentration tests revealed that PAIC exhibited antibacterial activity against Staphylococcus aureus, Proteus mirabilis and Klebsiella pneumonae whereas PAIC/Ag nanocomposite showed antibacterial activity against Enterococcus faecalis and K. pneumonae. © 2012 Society of Chemical Industry     

Bioactive glass particles as multi-functional therapeutic carriers against antibiotic-resistant bacteria

The development of antibiotic resistance in pathogenic bacteria like Staphylococcus aureus calls for novel approaches to cope with the limited availability of effective antibacterial options. This work aims to develop a site-specific drug-delivery multifunctional vehicle with the ability to clear resistant bacteria while promoting the healing of the surrounding damaged tissue. The use of silver-doped microparticles (Ag–BG) is proposed as a platform to deliver vancomycin against MRSA, which under growth-arrested conditions exhibits resistance to vancomycin. Ag–BG caged vancomycin within the Ca–P deposits resulted from the ion exchange between surface and medium, with a loading efficiency higher than 50% after 6 h of uptake. The drug was always released above the minimum inhibitory concentration against MRSA. The Ag–BG@vanc conjugate presented strong antibacterial properties against metabolically impaired bacteria, which can tolerate high concentrations of vancomycin. Ag–BG@vanc was more lethal for MRSA than Ag–BG alone, due to its capability to synergize with antibiotics. The presence of Ca–P deposits and antibiotics at the Ag–BG surface did not compromise its biological properties since the Ag–BG@vanc conjugate still promoted the cell proliferation of human pre-osteoblast cells. These properties of multifunctional Ag–BG@vanc can provide new hope to fight antibiotic resistance and simultaneously promote bone regeneration holding great potential.     

Scaffold‐Hopping of Multicationic Amphiphiles Yields Three New Classes of Antimicrobials

Quaternary ammonium compounds (QACs) are a vital class of antiseptics. Recent investigations into their construction are uncovering novel and potent multicationic variants. Based on a trisQAC precedent, we have implemented a scaffold‐hopping approach to develop alternative QAC architectures that display 1–3 long alkyl chains in specific projections from cyclic and branched core structures bearing 3–4 nitrogen atoms. The preparation of 30 QAC structures allowed for correlation of scaffold structure with antimicrobial activity. We identified QACs with limited conformational flexibility that have improved bioactivity against planktonic bacteria as compared to their linear counterparts. We also confirmed that resistance, as evidenced by an increased minimum inhibitory concentration (MIC) for methicillin‐resistant Staphylococcus aureus (MRSA) compared to methicillin‐susceptible Staphylococcus aureus (MSSA), can reduce efficacy up to 64‐fold for monocationic QACs. Differentiation of antimicrobial and anti‐biofilm activity, however, was not observed, suggesting that these compounds utilize a non‐specific mode of eradication.     

Surface grafting of polyester fiber with chitosan and the antibacterial activity of pathogenic bacteria

Three polyesters—poly(ethylene terephthalate), poly(2‐methyl‐1,3‐propylene terephthalate‐co‐ethylene terephthalate), and poly(1,4‐cyclohexylene terephthalate‐co‐ethylene terephthalate)—were preirradiated with ⁶⁰Co‐γ‐rays. Then, acrylic acid and N‐vinylformamide were grafted to these irradiated fibers. Fibers grafted with N‐vinylformamide were further hydrolyzed with acid so that the amide groups would convert into amino groups, and they were treated with glutaraldehyde so that aldehyde groups would be introduced. Chitosan or chitooligosaccharide was then grafted to these fibers via either esterification or imine formation. Four pathogenic bacteria—methicillin‐resistant Staphylococcus aureus‐1 (MRSA), Staphylococcus aureus‐2, Escherichid coli, and Pseudomonas aeruginosa—were tested to determine the antibacterial activities of chitosan‐grafted and chitooligosaccharide‐grafted fibers. The results showed that grafting chitosan via imine formation could achieve a higher surface density for amino groups and give higher antibacterial activity to those four bacteria tested. The antibacterial activity for E. coli was the highest and that for MRSA was the lowest among the four bacteria tested. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2977–2983, 2002     

Antibacterial Small Molecules That Potently Inhibit Staphylococcus aureus Lipoteichoic Acid Biosynthesis

The rise of antibiotic resistance, especially in Staphylococcus aureus, and the increasing death rate due to multiresistant bacteria have been well documented. The need for new chemical entities and/or the identification of novel targets for antibacterial drug development is high. Lipoteichoic acid (LTA), a membrane-attached anionic polymer, is important for the growth and virulence of many Gram-positive bacteria, and interest has been high in the discovery of LTA biosynthesis inhibitors. Thus far, only a handful of LTA biosynthesis inhibitors have been described with moderate (MIC=5.34 μg mL⁻¹) to low (MIC=1024 μg mL⁻¹) activities against S. aureus. Herein we describe the identification of novel compounds that potently inhibit LTA biosynthesis in S. aureus, displaying impressive antibacterial activities (MIC as low as 0.25 μg mL⁻¹) against methicillin-resistant S. aureus (MRSA). Under similar in vitro assay conditions, these compounds are 4-fold more potent than vancomycin and 8-fold more potent than linezolid against MRSA.     

Antibacterial activity of silver‐doped manganese dioxide nanoparticles on multidrug‐resistant bacteria

BACKGROUND: As a result of evolution of multiple drug resistance in human pathogens (bacteria) there is increasing demand for novel antibacterial agents, and recently, due to their high antibacterial and catalytic activities, metal nanoparticles have attracted the attention of researchers and medical microbiologists worldwide. RESULTS: Ni‐, Ce‐ and Ag‐doped MnO₂ nanoparticles were synthesized by a co‐precipitation method. Antibacterial activity of these synthesized nanoparticles on methicillin‐resistant Staphylococcus aureus and lead‐resistant Pseudomonas aeruginosa strain 4EA was investigated using a disc diffusion method. Only Ag‐doped MnO₂ nanoparticles showed an antibacterial property against methicillin‐resistant Staphylococcus aureus and lead‐resistant Pseudomonas aeruginosa strain 4EA at low levels of 60 µg/disc and 85 µg/disc, respectively. Scanning electron microscopy and transmission electron microscopy (SEM‐TEM) coupled with energy dispersive X‐ray (EDX) analysis revealed the nano‐size and composition of these synthesized nanoparticles. CONCLUSION: It was confirmed through a disc diffusion method that chemically synthesized silver doped MnO₂ nanoparticles have antibacterial activity against multidrug‐resistant Staphylococcus aureus and lead‐resistant Pseudomonas aeruginosa strain 4EA at low levels therefore these nanoparticles can be employed to fight and prevent infections caused by multidrug‐resistant bacterial pathogens. © 2012 Society of Chemical Industry     

Building a Better Quaternary Ammonium Compound (QAC): Branched Tetracationic Antiseptic Amphiphiles

Bacteria contaminate surfaces in a wide variety of environments, causing severe problems across a number of industries. In a continuation of our campaign to develop novel antibacterial quaternary ammonium compounds (QACs) as useful antiseptics, we have identified a starting material bearing four tertiary amines, enabling the rapid synthesis of several tris‐ and tetracationic QACs. Herein we report the synthesis and biological activity of a series of 24 multiQACs deemed the “superT” family, and an investigation of the role of cationic charge in antimicrobial and anti‐biofilm activity, as well as toxicity. This class represents the most potent series of QACs reported to date against methicillin‐resistant Staphylococcus aureus (MRSA), with minimum inhibitory concentrations (MICs) and minimum biofilm eradication concentrations (MBECs) as low as 0.25 and 25 μm , respectively. Based on the significant cell‐surface‐charge differences between bacterial and eukaryotic cells, in certain cases we observed excellent efficacy‐to‐toxicity profiles, exceeding a 100‐fold differential. This work further elucidates the chemical underpinnings of disinfectant efficacy versus toxicity based on cationic charge.     

Synthesis and Antimicrobial Activities of Oximes Derived from O-Benzylhydroxylamine as FabH Inhibitors

Forty‐three oxime derivatives were synthesized by allowing O‐benzylhydroxylamines to react with primary benzaldehydes or salicylaldehydes; these products were gauged as potential inhibitors of β‐ketoacyl‐(acyl‐carrier‐protein) synthase III (FabH). Among the 43 compounds, 38 are reported herein for the first time. These compounds were assayed for antimicrobial activities against Escherichia coli, Pseudomonas aeruginosa, Pseudomonas fluorescens, Bacillus subtilis, Staphylococcus aureus, and Enterococcus faecalis. Compounds with prominent antibacterial activities were tested for their E. coli FabH inhibitory activities. 3‐((2,4‐Dichlorobenzyloxyimino)methyl)benzaldehyde O‐2,4‐dichlorobenzyl oxime ( 44 ) showed the best antibacterial activity, with minimum inhibitory concentrations of 3.13–6.25 μg mL^?1 against the tested bacterial strains, exhibiting the best E. coli FabH inhibitory activity, with an IC₅₀ value of 1.7 mM . Docking simulations were performed to position compound 44 into the E. coli FabH active site in order to determine the most probable binding conformation.     

Prenylated Flavonoids with Potential Antimicrobial Activity: Synthesis,Biological Activity,and In Silico Study

Prenylated flavonoids are an important class of naturally occurring flavonoids with important biological activity, but their low abundance in nature limits their application in medicines. Here, we showed the hemisynthesis and the determination of various biological activities of seven prenylated flavonoids, named 7–13, with an emphasis on antimicrobial ones. Compounds 9, 11, and 12 showed inhibitory activity against human pathogenic fungi. Compounds 11, 12 (flavanones) and 13 (isoflavone) were the most active against clinical isolated Staphylococcus aureus MRSA, showing that structural requirements as prenylation at position C-6 or C-8 and OH at positions C-5, 7, and 4′ are key to the antibacterial activity. The combination of 11 or 12 with commercial antibiotics synergistically enhanced the antibacterial activity of vancomycin, ciprofloxacin, and methicillin in a factor of 10 to 100 times against drug-resistant bacteria. Compound 11 combined with ciprofloxacin was able to decrease the levels of ROS generated by ciprofloxacin. According to docking results of S enantiomer of 11 with ATP-binding cassette transporter showed the most favorable binding energy; however, more studies are needed to support this result.     

Photocatalytic and photodisinfectant activity of sulfated and Eu doped anatase against clinically important microorganisms

Surface sulfation and Eu³⁺ doping of 0.2–2 µm anatase aggregates prepared by precipitation significantly increased their porosity, specific surface, crystallinity and photocatalytic activity in phenol photo-mineralization. Such large, porous clusters of photocatalysts containing nanocrystals with well developed crystallinity which sediment more quickly than nanopowder suspensions are advantageous in water treatment applications. Sulfated anatase co-doped with Eu³⁺ exhibited the highest photoactivity. This is composed of well developed crystallites in the 31–55 nm size-range, with evident faceting. Although the investigated powders showed very weak photo-disinfectant activity against Gram-negative Escherichia coli rods, they exhibit moderate efficacy against Gram-positive bacterial strains of methicillin resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis. The investigated powders, especially the Eu³⁺ doped ones, are highly active in elimination of the eukaryotic Candida albicans.