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PubMed2003

Structure of bacteriocin AS-48: from soluble state to membrane bound state.

The bacteriocin AS-48 is a membrane-interacting peptide, which displays a broad anti-microbial spectrum against Gram-positive and Gram-negative bacteria. The NMR structure of AS-48 at pH 3 has been solved. The analysis of this structure suggests that the mechanism of AS-48 anti-bacterial activity involves the accumulation of positively charged molecules at the membrane surface leading to a disruption of the membrane potential. Here, we report the high-resolution crystal structure of AS-48 and sedimentation equilibrium experiments showing that this bacteriocin is able to adopt different oligomeric structures according to the physicochemical environment. The analysis of these structures suggests a mechanism for molecular function of AS-48 involving a transition from a water-soluble form to a membrane-bound state upon membrane binding.

Bacterial Proteins↗
PubMed2003

Dendritic cells as a tool to combat infectious diseases.

Dendritic cells (DCs) form a network of potent antigen-presenting cells that initiate and amplify immune responses. The detection and capture of microorganisms by DCs trigger stimulus-specific maturation programs that enable DCs to convey pathogen-associated signals to the adaptive branch of the immune system. The appropriate activation of DCs is critical for their ability to direct the development of either a Th1 or a Th2 response, thereby determining the outcome of microbial infections. Advances in the understanding of DC interactions with microbes provide new concepts for immune interventions. In different models of infectious disease, it has been demonstrated that DCs can serve as vaccine carriers, mediating protection against various types of pathogens. The studies of the requirements of ex vivo manipulations of DCs may lead to the design of vaccines that induce protective immunity to infections by appropriate targeting of DCs in vivo.

Animals↗
PubMed2001

Formulation and evaluation of itraconazole via liquid crystal for topical delivery system.

Liquid crystal systems are used to tailor drug delivery from topical delivery system. Ternary polyoxyethylene [21] stearyl ether/ oil and water form liquid crystalline system cream, which has a potential as dosage form for 1% itraconazole as topical dermal drug delivery. Evaluation of the suggested formula was performed for the best physical performance, the compatibility of the components of lyotropic liquid crystal with itraconazole was conducted through polarized light microscopy, differential scanning calorimeter, thermogravimetric analysis and viscosity measurements. Fourier transform infrared spectroscopy has been studied. Furthermore, in vitro antimycotic inhibitory activity of 1% itraconazole from liquid crystal, was conducted using agar-cup method and Candida albicans as a test organism. The pH value of the cream was found to be 7.1, while when the drug was incorporated in the cream, the pH value was 6.7. The formula was examined under polarized microscope at 20x magnification and the birefringence that is characteristic of concentric lamellar liquid crystal was observed around the oil globules. Differential scanning calorimeter of itraconazole cream showed higher transition peak temperature at 120 degrees C for the hydrophilic gel phases. Fourier transform infrared spectroscopy revealed that there was no complex or any interaction between the surfactant and the drug. The microbial studies revealed that our formula had the highest zone of inhibition. The average +/- SD inhibition zone values of the test, control I and control II are 30.4+/-1.14, 19.6+/-1.14 and 14.8+/-0.83 mm, respectively. It was found that the test was significantly different from control I and control II, P=5.33x10(-6), 8.92x10(-5), respectively, so it may be concluded that incorporation of the drug in liquid crystal increased its antimicotic activity against Candida albicans.

Administration, Topical↗
PubMed2002

Sensory rhodopsin II: functional insights from structure.

Atomic resolution structures of a sensory rhodopsin phototaxis receptor in haloarchaea (the first sensory member of the widespread microbial rhodopsin family) have yielded insights into the interaction face with its membrane-embedded transducer and into the mechanism of spectral tuning. Spectral differences between sensory rhodopsin and the light-driven proton pump bacteriorhodopsin depend largely upon the repositioning of a conserved arginine residue in the chromophore-binding pocket. Information derived from the structures, combined with biophysical and biochemical analysis, has established a model for receptor activation and signal relay, in which light-induced helix tilting in the receptor is transmitted to the transducer by lateral transmembrane helix-helix interactions.

Archaeal Proteins↗
PubMed2007

Interplay among folding, sequence, and lipophilicity in the antibacterial and hemolytic activities of alpha/beta-peptides.

Host-defense peptides inhibit bacterial growth but manifest relatively little toxicity toward eukaryotic cells. Many host-defense peptides adopt alpha-helical conformations in which cationic side chains and lipophilic side chains are segregated to distinct regions of the molecular surface ("globally amphiphilic helices"). Several efforts have been made to develop unnatural oligomers that mimic the selective antibacterial activity of host-defense peptides; these efforts have focused on the creation of molecules that are globally amphiphilic in the preferred conformation. One such endeavor, from our laboratories, focused on helix-forming alpha/beta-peptides, i.e., oligomers containing a 1:1 pattern of alpha- and beta-amino acid residues in the backbone [Schmitt, M. A.; Weisblum, B.; Gellman, S. H. J. Am. Chem. Soc. 2004, 126, 6848-6849]. We found, unexpectedly, that the most favorable biological activity profile was displayed by a "scrambled" sequence, which was designed not to be able to form a globally amphiphilic helix. Here we report new data, involving an expanded set of alpha/beta-peptides, from experiments designed to elucidate the origins of this surprising result. In addition, we evaluate the susceptibility of alpha/beta-peptides to proteolytic degradation. Our results support the hypothesis that the ability to adopt a globally amphiphilic helical conformation is not a prerequisite for selective antibacterial activity. This conclusion represents a significant advance in our understanding of the relationship among molecular composition, conformation, and biological activity. Our results should therefore influence the design of other unnatural oligomers intended to function as antibacterial agents.

Anti-Bacterial Agents↗
PubMed1990

Synthesis and structure-activity relationships of 5-substituted 6,8-difluoroquinolones, including sparfloxacin, a new quinolone antibacterial agent with improved potency.

A series of 5,7-disubstituted 1-cyclopropyl-6,8-difluoro-4(1H)-oxoquinoline-3-carboxylic acids (10-36) were prepared; the C-5 substituent in these compounds comprised halo, hydroxy, mercapto, and amino groups and the C-7 functional group included variously substituted piperazines. In vitro antibacterial screening results indicated that the amino group was optimal among the C-5 substituents. A combination of the C-5 amino group and the C-7 3,5-dimethylpiperazinyl appendage in this series conferred the best overall antibacterial property with lack of adverse drug interactions. Compound 36k [named sparfloxacin, originally AT-4140, 5-amino-1-cyclopropyl-6,8-difluoro-7-(cis-3,5-dimethyl-1-piperazinyl)- 4(1H)-oxoquinoline-3-carboxylic acid] was superior to ciprofloxacin in both in vitro and in vivo potency and hence was selected as a promising candidate for an improved therapeutic agent.

4-Quinolones↗
PubMed1978

Synthesis and biological activity of new 2-nitroimidazole derivatives.

In an earlier paper we described the synthesis and the antitrichomonas activity of 2-nitro-alpha,alpha,1-trimethyl-1H-imidazole-5-methanol (2). Starting from this compound, several derivatives have been synthesized. Among these, the phenyl carbonate 8 has been shown to possess activity equal to that of 2 and to be less toxic. This compound therefore is interesting in comparison with some antitrichomonas agents currently in use clinically. Before undertaking an in-depth investigation, compound 8 was subjected to some studies to see whether it has any effects on the central nervous system (CNS). Preliminary results show that, at therapeutic doses, it might induce unwanted CNS effects to a lesser degree than metronidazole.

Animals↗
PubMed2003

Role of the glycopeptide framework in the antibacterial activity of hydrophobic derivatives of glycopeptide antibiotics.

The antibacterial properties of glycopeptide antibiotics are based on their interaction with the d-Ala-d-Ala containing pentapeptide of bacterial peptidoglycan. The hydrophobic amides of vancomycin (1), teicoplanin (2), teicoplanin aglycon (3), and eremomycin (4) were compared with similar amides of minimally or low active des-(N-methyl-d-leucyl)eremomycin (5), eremomycin aglycon (6), des-(N-methyl-d-leucyl)eremomycin aglycon (7), and a teicoplanin degradation product TB-TPA (8). All hydrophobic amides of 1, 3, 4, and 6 were almost equally active against glycopeptide-resistant enterococci (GRE) [minimum inhibitory concentrations (MIC) <or= 4 microg/mL] and had better activity against Gram-positive strains sensitive to glycopeptides than against GRE. Extensive degradation of the glycopeptide framework in amides of 7 and 8 led to a decrease of anti-GRE activity (MIC = 16-64 microg/mL), and for these derivatives MIC values for bacterial strains sensitive and resistant to glycopeptides were very close. These results suggest that in sensitive bacteria two mechanisms of action are operating for the hydrophobic derivatives of glycopeptide antibiotics with the nondamaged peptide core-interaction with the d-Ala-d-Ala moiety and the inhibition of bacterial membrane bound enzymatic reactions, whereas for GRE lacking the d-Ala-d-Ala fragment, only the second mechanism is operating. It appears that a minimal glycopeptide core is required for activity, and that more extensive degradation results in a serious decrease of antibacterial activity.

Anti-Bacterial Agents↗
PubMed2004

Hydrophobic acetal and ketal derivatives of mannopeptimycin-alpha and desmethylhexahydromannopeptimycin-alpha: semisynthetic glycopeptides with potent activity against Gram-positive bacteria.

The effect of introducing hydrophobic groups onto the disaccharide portion of the mannopeptimycins has been examined. Under acid-catalyzed conditions dimethyl acetals and ketals react on the terminal mannose of the disaccharide moiety of mannopeptimycin-alpha and the cyclohexylalanyl analogue 2. The preferentially formed monofunctionalized 4,6-acetals and -ketals display potent antibacterial activities against Gram-positive microorganisms, including MRSA, PRSP, and VRE pathogens.

Acetals↗
PubMedDate not supplied

A model for diffusion controlled bioavailability of crude oil components.

Crude oil is a complex mixture of several different structural classes of compounds including alkanes, aromatics, heterocyclic polar compounds, and asphaltenes. The rate and extent of microbial degradation of crude oil depends on the interaction between the physical and biochemical properties of the biodegradable compounds and their interactions with the non-biodegradable fraction. In this study we have systematically altered the concentration of non-biodegradable material in the crude oil and analyzed its impact on transport of the biodegradable components of crude oil to the microorganisms. We have also developed a mathematical model that explains and accounts for the dependence of biodegradation of crude oil through a putative bioavailability parameter. Experimental results indicate that as the asphaltene concentration in oil increases, the maximum oxygen uptake in respirometers decreases. The mathematically fitted bioavailability parameter of degradable components of oil also decreases as the asphaltene concentration increases.

Algorithms↗
PubMed2002

Chemical ecology of marine microbial defense.

Because marine animals and plants are continuously exposed to a large diversity of potentially harmful microorganisms, it seems reasonable to hypothesize that potential hosts might produce bioactive compounds to deter microbial attack. However, little is known about how host metabolites may defend against harmful microbes or facilitate the growth or colonization of helpful symbionts. While there is a large body of literature describing the antimicrobial activities of marine secondary metabolites, we are only now beginning to understand how these compounds function in an ecological context. For example, there is mounting evidence that nontoxic concentrations of secondary metabolites can have significant effects on microbial behavior, suggesting that certain host-microbe interactions are chemically mediated. Herein, we discuss the importance of employing ecologically relevant assays to elucidate microbiological effects and the need to develop a better understanding of host-microbe associations within an ecologically realistic context. Continued research in this field along with improved techniques will certainly provide further insight into how microbes have influenced the evolution of secondary metabolite production in marine organisms.

Animal Population Groups↗
PubMed2001

Effect of physical factors on the production of bacteriocin from Pediococcus acidilactici ITV 26.

The effect of pH, temperature and agitation on growth and bacteriocin production by Pediococcus acidilactici ITV 126 was investigated. Experiments were made in flasks containing MRS medium at 30 to 40 degrees C, pH 5 to 7 and agitation 0 to 200 rpm. Factor levels were arranged in a 2(3) factorial design with central and axial points. Anova and Tukey paired comparison tests showed that a temperature of 35 degrees C favored bacteriocin production, whereas 40 degrees C was best for cell growth. A statistical interaction of temperature and agitation was observed affecting microbial growth. pH 5 favored both cell growth and bacteriocin production.

Bacteriocins↗
PubMed1992

The influence of serum proteins on biological activity of anticandidal peptides containing N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid.

The binding of several anticandidal peptides containing N3-(4-methoxyfumaroyl)-L-2,3-diaminopropanoic acid (FMDP) to serum proteins was studied using equilibrium dialysis. The affinity of these FMDP-peptides for serum albumin was low and well correlated with their biological activity against Candica albicans ATCC 26278 in serum albumin solution. This binding did not affect the biological activity of FMDP-peptides. On the other hand, substantial raising of MIC values was observed when anticandidal activity of FMDP peptides was assayed in the presence of complete serum proteins. This effect was likely to be a result of interaction with non-albumin components of serum proteins. Preliminary evidence points to the possibility of non-specific interaction with components containing sulfhydryl groups. In this study Nva-FMDP-Nva peptide was shown to be the most active compound in the serum protein solution. Moreover Nva-FMDP-Nva was most resistant to inactivation by serum components in comparison to other FMDP-peptides.

Animals↗
PubMed1993

In vitro activity of cefodizime (HR-221) in combination with beta-lactamase inhibitors.

Cefodizime (formerly HR221) was tested either for in vitro microbiological activity or for its stability to beta-lactamases in the presence of two beta-lactamase inhibitors (clavulanic acid, tazobactam). Cefodizime was a poor substrate of class C enzymes but hyperproducer strains were generally resistant with or without a beta-lactamase inhibitor used in combination. On the contrary, class A enzymes were able to hydrolyze cefodizime. However, strains expressing class A beta-lactamase were susceptible to cefodizime in combination with clavulanic acid.

Anti-Bacterial Agents↗
PubMed2005

Assessing in vitro combinations of antifungal drugs against yeasts and filamentous fungi: comparison of different drug interaction models.

Non-parametric and parametric approaches of two competing zero-interaction theories--the Loewe additivity and the Bliss independence - were evaluated for analyzing the in vitro interactions of various antifungal drugs. Fifty-one data sets, derived from three drug combinations, tested in triplicate against 17 clinical yeast and mold isolates with a two-dimensional checkerboard microdilution technique, were selected to span from strong synergy to strong antagonism. These were analyzed with the standard FIC index model and modern concentration-effect response surface models: the fully parametric model developed by Greco et al. and the 3-D analysis developed by Prichard et al. The FIC index model is subjective, sensitive to experimental errors and resulted in approximated results and variable conclusions depending on the MIC endpoints determined and interpretation endpoints used. By using the MIC-2 endpoint (lowest drug concentration showing 50% of growth) for calculating the FIC indices, problems due to trailing phenomena were reduced and weak interactions could be detected; higher levels of reproducibility and agreement with the other models were achieved using the MIC-0 and MIC-1 (lowest drug concentration showing 10 and 25% of growth, respectively). High reproducibility was achieved in interpreting the FIC indices when the cutoffs of 0.25 and 4 (for single experiments) and the cutoff of 1 (for replicates) were used for defining the limits of additivity/indifference. Although the fully parametric Greco model did not describe precisely the entire response surface of all antifungal drug interactions, it was able to differentiate synergistic from non-synergistic interactions with a non-unit, reproducible, concentration-independent interaction parameter, including its uncertainty, without requiring replication. The Bliss independence based models resulted in mosaics of synergistic and antagonistic combinations, raising questions about the concentration-dependent nature of antifungal drug interaction. The sum of all statistically significant interactions were used as a summary interaction parameter for the entire response surface, concluding synergy or antagonism when it was positive or negative, respectively. The cutoffs of 100% and 200% were used to distinguish weak and moderate interactions, respectively in 12-16 x 8-12 checkerboard formats. Semi-parametric approaches need particular care as experimental errors are not eliminated from the entire response surface.

Antifungal Agents↗
PubMed2003

Voriconazole: a new triazole antifungal agent.

Voriconazole is a second-generation azole antifungal agent that shows excellent in vitro activity against a wide variety of yeasts and molds. It can be given by either the intravenous or the oral route; the oral formulation has excellent bioavailability. The side effect profile of voriconazole is unique in that non-sight-threatening, transient visual disturbances occur in approximately 30% of patients given the drug. Rash (which can manifest as photosensitivity) and hepatitis also occur. The potential for drug-drug interactions is high and requires that careful attention be given to dosage regimens and monitoring of serum levels and effects of interacting drugs. Voriconazole has been approved for the treatment of invasive aspergillosis and refractory infections with Pseudallescheria/Scedosporium and Fusarium species, and it will likely become the drug of choice for treatment of serious infections with those filamentous fungi.

Antifungal Agents↗
PubMedDate not supplied

Synergy of fluoroquinolones with other antimicrobial agents.

Synergy resulting from the combination of ciprofloxacin and an antipseudomonal penicillin has been reported for 20%-50% of isolates of Pseudomonas aeruginosa. A similar effect has also been reported for the combination of ciprofloxacin and fosfomycin. In contrast, the combination of quinolones and aminoglycosides rarely showed synergy when tested against P. aeruginosa. Most studies have shown that the combination of beta-lactams or aminoglycosides with quinolones is indifferent against Escherichia coli, Klebsiella species, Enterobacter species, Citrobacter species, and Serratia species. The combination of ciprofloxacin and chloramphenicol can be antagonistic against E. coli. In general, the combination of quinolone antibiotics with other drugs tested against staphylococci, enterococci, and anaerobic species has shown indifference. The neutropenic mouse model of infection has demonstrated the synergistic effect of ciprofloxacin plus antipseudomonal penicillins; the combination of ciprofloxacin and rifampin has been superior to single agents in experimental Staphylococcus aureus osteomyelitis. Ciprofloxacin has been the quinolone studied most thoroughly, and few data are available about the combination of other quinolones with other antimicrobial agents. Overall, the occurrence of synergy when quinolones are combined with other antimicrobial agents is infrequent, and clinical studies that demonstrate the clinical relevance of data from in vitro and animal models of infection are not available. However, data from in vitro and animal model studies indicate that the combination of a quinolone with other antimicrobial agents rarely results in antagonism.

4-Quinolones↗