Mihaela Perić

Effects of an Efflux Mechanism and Ribosomal Mutations on Macrolide Susceptibility of Haemophilus influenzae Clinical Isolates

ABSTRACT This study investigated macrolide resistance mechanisms in clinical Haemophilus influenzae strains with different levels of susceptibility to macrolides. A total of 6,382 isolates were collected during the Alexander Project from 1997 to 2000. For 96.9% of these isolates, the azithromycin MICs were 0.25 to 4 μg/ml, and these were defined as baseline strains. For 1.8% of the isolates, the azithromycin MICs were lower (<0.25 μg/ml), and for 1.3% of the isolates, the MICs were higher (>4 μg/ml). These isolates were defined as hypersusceptible and high-level macrolide-resistant strains, respectively. To identify the mechanisms associated with these three susceptibility patterns, representative strains were studied for the presence of macrolide efflux pumps and for ribosomal alterations. Macrolide efflux was studied by measuring the accumulation of radioactive azithromycin and clarithromycin in the presence or absence of carbonyl cyanide m-chlorophenylhydrazone (CCCP), a protonophore. Treatment with CCCP increased the accumulation of macrolides in baseline as well as high-level resistant strains, demonstrating the presence of an efflux mechanism, but not in the 20 hypersusceptible strains tested. Among the 31 strains studied that showed high-level resistance to both azithromycin and clarithromycin, 28 had ribosomal alterations, 7 had mutations in ribosomal protein L4, 11 had mutations in L22, 2 had mutations in 23S rRNA, 8 had multiple mutations, and 3 had no mutations. From these results, we conclude that the vast majority (>98%) of H. influenzae strains have a macrolide efflux mechanism, with a few of these being hyperresistant (1.3%) due to one or several ribosomal mutations. Occasional hypersusceptible strains (1.8%) were found and had no macrolide resistance mechanisms and appeared to be the only truly macrolide-susceptible variants of H. influenzae.

The clinical use of bone morphogenetic proteins revisited: a novel biocompatible carrier device OSTEOGROW for bone healing

PurposeThe purpose of this study was to revise the clinical use of commercial BMP2 (Infuse) and BMP7 (Osigraft) based bone devices and explore the mechanism of action and efficacy of low BMP6 doses in a novel whole blood biocompatible device OSTEOGROW.MethodsComplications from the clinical use of BMP2 and BMP7 have been systemically reviewed in light of their role in bone remodeling. BMP6 function has been assessed in Bmp6-/- mice by μCT and skeletal histology, and has also been examined in mesenchymal stem cells (MSC), hematopoietic stem cells (HSC) and osteoclasts. Safety and efficacy of OSTEOGROW have been assessed in rats and rabbits.ResultsClinical use issues of BMP2 and BMP7 have been ascribed to the limited understanding of their role in bone remodeling at the time of device development for clinical trials. BMP2 and BMP7 in bone devices significantly promote bone resorption leading to osteolysis at the endosteal surfaces, while in parallel stimulating exuberant bone formation in surrounding tissues. Unbound BMP2 and BMP7 in bone devices precipitate on the bovine collagen and cause inflammation and swelling. OSTEOGROW required small amounts of BMP6, applied in a biocompatible blood coagulum carrier, for stimulating differentiation of MSCs and accelerated healing of critical size bone defects in animals, without bone resorption and inflammation. BMP6 decreased the number of osteoclasts derived from HSC, while BMP2 and BMP7 increased their number.ConclusionsCurrent issues and challenges with commercial bone devices may be resolved by using novel BMP6 biocompatible device OSTEOGROW, which will be clinically tested in metaphyseal bone fractures, compartments where BMP2 and BMP7 have not been effective.

In Vitro Selection of Resistance in Haemophilus influenzae by Amoxicillin-Clavulanate, Cefpodoxime, Cefprozil, Azithromycin, and Clarithromycin

ABSTRACT Abilities of amoxicillin-clavulanate, cefpodoxime, cefprozil, azithromycin, and clarithromycin to select resistant mutants of Haemophilus influenzae were tested by multistep and single-step methodologies. For multistep studies, 10 random strains were tested: 5 of these were β-lactamase positive. After 50 daily subcultures in amoxicillin-clavulanate, MICs did not increase more than fourfold. However, cefprozil MICs increased eightfold for one strain. Clarithromycin and azithromycin gave a >4-fold increase in 8 and 10 strains after 14 to 46 and 20 to 50 days, respectively. Mutants selected by clarithromycin and azithromycin were associated with mutations in 23S rRNA and ribosomal proteins L4 and L22. Three mutants selected by clarithromycin or azithromycin had alterations in ribosomal protein L4, while five had alterations in ribosomal protein L22. Two mutants selected by azithromycin had mutations in the gene encoding 23S rRNA: one at position 2058 and the other at position 2059 (Escherichia coli numbering), with replacement of A by G. One clone selected by clarithromycin became hypersusceptible to macrolides. In single-step studies azithromycin and clarithromycin had the highest mutation rates, while amoxicillin-clavulanate had the lowest. All resistant clones were identical to parents as observed by pulsed-field gel electrophoresis. The MICs of azithromycin for azithromycin-resistant clones were 16 to >128 μg/ml, and those of clarithromycin for clarithromycin-resistant clones were 32 to >128 μg/ml in multistep studies. For strains selected by azithromycin, the MICs of clarithromycin were high and vice versa. After 50 daily subcultures in the presence of drugs, MICs of amoxicillin-clavulanate and cefpodoxime against H. influenzae did not rise more than fourfold, in contrast to cefprozil, azithromycin, and clarithromycin, whose MICs rose to variable degrees.

Azetidinone-isothiazolidinones: Stereoselective synthesis and antibacterial evaluation of new monocyclic beta-lactams

A simple and efficient procedure for the stereoselective synthesis of new azetidinone-isothiazolidinones has been developed. New compounds were tested in vitro on a panel of Gram-positive and Gram-negative bacterial pathogens, some of them showing weak antibacterial activity.

Activity of nine oral agents against gram-positive and gram-negative bacteria encountered in community-acquired infections: use of pharmacokinetic/pharmacodynamic breakpoints in the comparative assessment of beta-lactam and macrolide antimicrobial agents.

BACKGROUND The application of pharmacokinetic (PK) and pharmacodynamic (PD) data in conjunction with minimum inhibitory concentrations (MICs) of antibacterial agents has been shown to allow for improved selection and appropriate dosing of antimicrobial agents for specific infections, increasing the likelihood of bacteriologic cure and, through this, reducing the risk for the development of resistant organisms. OBJECTIVES This study was undertaken to provide data on current levels of resistance among common community-acquired bacterial species to 7 betalactam antimicrobial agents (including the combination product amoxicillin/clavulanate), azithromycin, and clarithromycin, determined through application of the PK/PD breakpoints based on time-above-MIC for the beta-lactams and the nonazalide macrolide clarithromycin, and on 24-hour serum area under the curve divided by MIC for the azalide macrolide azithromycin. METHODS The antimicrobial products tested were amoxicillin/clavylanate, cefpodoxime, cefdinir, cefditoren, cefprozil, cefuroxime, cefixime, azithromycin, and clarithromycin. The bacterial species comprised 70 penicillin-susceptible, 68 penicillin-intermediate, and 69 penicillin-resistant strains of Streptococcus pneumoniae; 46 beta-lactamase-positive and 54 beta-lactamase-negative strains of Haemophilus influenzae; 49 strains of Moraxella catarrhalis; and 100 methicillin-sensitive strains of Staphylococcus aureus (MSSA). Strains were isolated from clinical specimens obtained from outpatient-acquired infections in 1 clinical center in the Northeast and 1 in the north-central area of the United States within the past 2 years. National Committee for Clinical Laboratory Standards microdilution MIC methodology was used. PK/PD breakpoints were obtained from previously published studies and were based on blood values. RESULTS Amoxicillin/clavulanate was the product to which the greatest percentage of susceptible, intermediate, and resistant strains of pneumococci were sensitive at the PK/PD breakpoint, followed by cefditoren, cefpodoxime, cefuroxime, cefdinir, and cefprozil. None of the cephalosporins were active against penicillin-resistant pneumococci. Cefditoren and cefpodozime were the agents to which the greatest percentage of beta-lactamase-positive and beta-lactamase-negative strains of H influenzae were sensitive, followed by amoxicillin/clavulanate, cefdinir, and cefuroxime. Cefprozil was inactive against H influenzae. All of the beta-lactam products were active against M catarrhalis. All but cefpodoxime, cefditoren, and cefixime were active against MSSA. CONCLUSIONS In this study, based on PK/PD breakpoints, amoxicillin/clavulanate had the best overall activity of the 9 antimicrobial products tested. Cefpodoxime and cefditoren were active against >or=90% of strains of penicillin-susceptible and penicillin-intermediate pneumococci, H influenzae, and M catarrhalis. The macrolides azithromycin and clarithromycin were active against penicillin-susceptible and penicillin-intermediate pneumococci and M catarrhalis; they were inactive against H influenzae and penicillin-resistant pneumococci.

Antimalarial activity of 9a-N substituted 15-membered azalides with improved in vitro and in vivo activity over azithromycin.

Novel classes of antimalarial drugs are needed due to emerging drug resistance. Azithromycin, the first macrolide investigated for malaria treatment and prophylaxis, failed as a single agent and thus novel analogues were envisaged as the next generation with improved activity. We synthesized 42 new 9a-N substituted 15-membered azalides with amide and amine functionalities via simple and inexpensive chemical procedures using easily available building blocks. These compounds exhibited marked advances over azithromycin in vitro in terms of potency against Plasmodium falciparum (over 100-fold) and high selectivity for the parasite and were characterized by moderate oral bioavailability in vivo. Two amines and one amide derivative showed improved in vivo potency in comparison to azithromycin when tested in a mouse efficacy model. Results obtained for compound 6u, including improved in vitro potency, good pharmacokinetic parameters, and in vivo efficacy higher than azithromycin and comparable to chloroquine, warrant its further development for malaria treatment and prophylaxis.

Modulating composition and metabolic activity of the gut microbiota in IBD patients

The healthy intestine represents a remarkable interface where sterile host tissues come in contact with gut microbiota, in a balanced state of homeostasis. The imbalance of gut homeostasis is associated with the onset of many severe pathological conditions, such as inflammatory bowel disease (IBD), a chronic gastrointestinal disorder increasing in incidence and severely influencing affected individuals. Despite the recent development of next generation sequencing and bioinformatics, the current scientific knowledge of specific triggers and diagnostic markers to improve interventional approaches in IBD is still scarce. In this review we present and discuss currently available and emerging therapeutic options in modulating composition and metabolic activity of gut microbiota in patients affected by IBD. Therapeutic approaches at the microbiota level, such as dietary interventions alone or with probiotics, prebiotics and synbiotics, administration of antibiotics, performing fecal microbiota transplantation (FMT) and the use of nematodes, all represent a promising opportunities towards establishing and maintaining of well-being as well as improving underlying IBD symptoms.

Synthesis and structure–activity relationship of amidine derivatives of 3, 4-ethylenedioxythiophene as novel antibacterial agents

Current antibacterial chemotherapeutics are facing an alarming increase in bacterial resistance pressuring the search for novel agents that would expand the available therapeutic arsenal against resistant bacterial pathogens. In line with these efforts, a series of 9 amidine derivatives of 3,4-ethylenedioxythiophene were synthesized and, together with 18 previously synthesized analogs, evaluated for their relative DNA binding affinity, in vitro antibacterial activities and preliminary in vitro safety profile. Encouraging antibacterial activity of several subclasses of tested amidine derivatives against Gram-positive (including resistant MRSA, MRSE, VRE strains) and Gram-negative bacterial strains was observed. The bis-phenyl derivatives were the most antibacterially active, while compound 19 from bis-benzimidazole class exhibited the widest spectrum of activity (with MIC of 4, 2, 0.5 and ≤0.25 μg/ml against laboratory strains of Staphyloccocus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Moraxella catarrhalis, respectively and 4-32 μg/ml against clinical isolates of sensitive and resistant S. aureus, Staphylococcus epidermidis and Enterococcus faecium) and also demonstrated the strongest DNA binding affinity (ΔTm of 15.4 °C). Asymmetrically designed compounds and carboxamide-amidines were, in general, less active. Molecular docking indicated that the shape of the 3,4-ethylenedioxythiophene derivatives and their ability to form multiple electrostatic and hydrogen bonds with DNA, corresponds to the binding modes of other minor-groove binders. Herein reported results encourage further investigation of this class of compounds as novel antibacterial DNA binding agents.

1,2,3-Triazole pharmacophore-based benzofused nitrogen/sulfur heterocycles with potential anti-Moraxella catarrhalis activity.

Versatile 1,2,3-triazole pharmacophore-based benzofused heterocycles containing halogen-substituted aromatic (9-17 and 25-28), 7-substituted coumarin (18-23 and 29-30) or penciclovir-like subunit (31a,b-38a) were designed and synthesized to evaluate their antibacterial activities against selected Gram-positive and Gram-negative bacteria. Hybridization approach using environmentally friendly Cu(I)-catalyzed click reaction under microwave irradiation was adopted in the synthesis of regioselective 1,4-disubstituted 1,2,3-triazole tethered heterocycles (9-23 and 25-30), while post-N-alkylation of NH-1,2,3-triazoles afforded both 2,4- (31a-38a) and 1,4-disubstituted (31b-33b, 35b-37b) 1,2,3-triazole regioisomers. The compounds 18-23 and 25-30 revealed fluorescence in the violet region of the visible spectrum with a strong influence of phenyl spacer in 25-30 on both wavelength and emission intensity. Fusion of selected subunits led to new hybrid architecture, benzothiazole-1,2,3-triazole-coumarin 29 that demonstrated extremely narrow spectrum activity towards fastidious Gram-negative bacteria Moraxella catarrhalis. Selected hybrid showed the potency against Moraxella catarrhalis (MIC⩽0.25μg/mL) comparable to that of reference antibiotic azithromycin, which suggested that further investigations are necessary to optimize this potential hit compound as a new anti-Moraxella catarrhalis agent.

An efficient and convenient microwave-assisted chemical synthesis of (thio)xanthones with additional in vitro and in silico characterization.

Xanthones and their thio-derivatives are a class of pleiotropic compounds with various reported pharmacological and biological activities. Although these activities are mainly determined in laboratory conditions, the class itself has a great potential to be utilized as promising chemical scaffold for the synthesis of new drug candidates. One of the main obstacles in utilization of these compounds was related to the difficulties in their chemical synthesis. Most of the known methods require two steps, and are limited to specific reagents not applicable to a large number of starting materials. In this paper a new and improved method for chemical synthesis of xanthones is presented. By applying a new procedure, we have successfully obtained these compounds with the desired regioselectivity in a shorter reaction time (50s) and with better yield (>80%). Finally, the preliminary in vitro screenings on different bacterial species and cytotoxicity assessment, as well as in silico activity evaluation were performed. The obtained results confirm potential pharmacological use of this class of molecules.