bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Experimental Method to Estimate Stress-Strain Behavior of Intact Coronary Arteries Using Intravascular Ultrasound (IVUS)
Authors: Tajaddini Azita , Kilpatrick Deborah L. , Vince D. Geoffrey
Published: February 2003

Most arterial mechanics studies have focused on excised non-coronary vessels, with few studies validating the application of ex-vivo results to in-vivo conditions. A method was developed for testing the mechanical properties of intact left anterior descending coronary arteries under a variety of conditions. Vascular deformation and pressure were simultaneously measured with intravascular ultrasound and a pressure transducer guidewire, respectively. Results suggest the importance of understanding in-vivo factors such as myocardial support, vascular tone and local pressure fluctuations when applying ex-vivo coronary characterization data. With further development, this method can more accurately characterize the true in-vivo constitutive behavior in normal and atherosclerotic coronaries.
Viscoelastic Characterization of Peripapillary Sclera: Material Properties by Quadrant in Rabbit and Monkey Eyes
Authors: Downs J. Crawford , Suh J-K. Francis , Thomas Kevin A. , Bellezza Anthony J. , Burgoyne Claude F. , Hart Richard T.
Published: February 2003

In this report we characterize the viscoelastic material properties of peripapillary sclera from the four quadrants surrounding the optic nerve head in both rabbit and monkey eyes. Scleral tensile specimens harvested from each quadrant were subjected to uniaxial stress relaxation and tensile ramp to failure tests. Linear viscoelastic theory, coupled with a spectral reduced relaxation function, was employed to characterize the viscoelastic properties of the tissues. We detected no differences in the stress-strain curves of specimens from the four quadrants surrounding the optic nerve head (ONH) below a strain of 4 percent in either the rabbit or monkey. While the peripapillary sclera from monkey eyes is significantly stiffer (both instantaneously and in equilibrium) and relaxes more slowly than that from rabbits, we detected no differences in the viscoelastic material properties (tested at strains of 0–1 percent) of sclera from the four quadrants surrounding the ONH within either species group.
Influence of Fixed Charge Density Magnitude and Distribution on the Intervertebral Disc: Applications of a Poroelastic and Chemical Electric (PEACE) Model
Authors: Iatridis James C. , Laible Jeffrey P. , Krag Martin H.
Published: February 2003

A 3-dimensional formulation for a poroelastic and chemical electric (PEACE) model is presented and applied to an intervertebral disc slice in a 1-dimensional validation problem and a 2-dimensional plane stress problem. The model was used to investigate the influence of fixed charge density magnitude and distribution on this slice of disc material. Results indicated that the mechanical, chemical, and electrical behaviors were all strongly influenced by the amount as well as the distribution of fixed charges in the matrix. Without any other changes in material properties, alterations in the fixed charge density (proteoglycan content) from a healthy to a degenerated distribution will cause an increase in solid matrix stresses and can affect whether the tissue imbibes or exudes fluid under different loading conditions. Disc tissue with a degenerated fixed charge density distribution exhibited greater solid matrix stresses and decreased streaming potential, all of which have implications for disc nutrition, disc biomechanics, and tissue remodeling. It was also seen that application of an electrical potential across the disc can induce fluid transport.
Parameter Estimation in a Crossbridge Muscle Model
Authors: Lin David C. , Nichols T. Richard
Published: February 2003

Models of muscle crossbridge dynamics have great potential for understanding muscle contraction and having a wide range of application. However, the estimation of many model parameters, most of which are difficult to measure, limits their applicability. This study developed a method of estimating parameters in the Distribution Moment crossbridge model from measurements of force-length and force-velocity relationships in cat soleus single muscle fibers. Analysis of the parameter estimates showed that the detachment rate parameters had more uncertainty than the attachment rate parameter, which could reflect physiological variations in the contractile protein content and in the response of muscle to lengthenings.
Experimental Flow Studies in Exact-Replica Phantoms of Atherosclerotic Carotid Bifurcations Under Steady Input Conditions
Authors: Bale-Glickman J. , Selby K. , Saloner D. , Savas¸ O¨.
Published: February 2003

Extensive flow studies are conducted in two carotid bifurcation flow phantoms. These phantoms exactly replicate the lumen of the plaque excised intact from two patients with severe carotid atherosclerosis. The input flow into the phantom’s common carotid artery is steady. Novel scanning techniques for flow visualization and particle image velocimetry are used. In addition, a novel boundary treatment technique is employed in velocimetry to extract first order accurate velocity gradients at walls. The data show that the flow fields are highly three-dimensional. Numerous separation and recirculation zones dominate the flow domain, except at the lowest Reynolds numbers. The separation regions are often so severe that highly directed internal jets form. At high Reynolds numbers, the flows become unsteady and chaotic, even though the input flow is steady. Flow fields have large regions of energetic flow and almost stagnant recirculation zones. These recirculation zones range in size from the full size of the arteries to zones within crevasses smaller than 1 mm. Velocity field and streamline patterns conform well to the lumen geometry. The streamlines are highly tortuous. Stagnation points correlate well with the topological features of the stenosis. Vorticity maps confirm the highly complex and three dimensional nature of the flow. Wall shear stresses at the stenoses are estimated to be on the order of 10 Pa. These studies conclusively show that the nature of the flow in the diseased bifurcation is primarily dictated by the lumen geometry.
The Merits of a Parallel Genetic Algorithm in Solving Hard Optimization Problems
Authors: van Soest A. J. Knoek , Casius L. J. R. Richard
Published: February 2003

A parallel genetic algorithm for optimization is outlined, and its performance on both mathematical and biomechanical optimization problems is compared to a sequential quadratic programming algorithm, a downhill simplex algorithm and a simulated annealing algorithm. When high-dimensional non-smooth or discontinuous problems with numerous local optima are considered, only the simulated annealing and the genetic algorithm, which are both characterized by a weak search heuristic, are successful in finding the optimal region in parameter space. The key advantage of the genetic algorithm is that it can easily be parallelized at negligible overhead.
On the Sensitivity of Wall Stresses in Diseased Arteries to Variable Material Properties
Authors: Williamson, S. D. , Lam, Y. , Younis, H. F. , Huang, H. , Patel, S. , Kaazempur-Mofrad, and M. R. , Kamm R. D.
Published: February 2003

Accurate estimates of stress in an atherosclerotic lesion require knowledge of the material properties of its components (e.g., normal wall, fibrous plaque, calcified regions, lipid pools) that can only be approximated. This leads to considerable uncertainty in these computational predictions. A study was conducted to test the sensitivity of predicted levels of stress and strain to the parameter values of plaque used in finite element analysis. Results show that the stresses within the arterial wall, fibrous plaque, calcified plaque, and lipid pool have low sensitivities for variation in the elastic modulus. Even a ±50% variation in elastic modulus leads to less than a 10% change in stress at the site of rupture. Sensitivity to variations in elastic modulus is comparable between isotropic nonlinear, isotropic nonlinear with residual strains, and transversely isotropic linear models. Therefore, stress analysis may be used with confidence that uncertainty in the material properties generates relatively small errors in the prediction of wall stresses. Either isotropic nonlinear or anisotropic linear models provide useful estimates, however the predictions in regions of stress concentration (e.g., the site of rupture) are somewhat more sensitive to the specific model used, increasing by up to 30% from the isotropic nonlinear to orthotropic model in the present example. Changes resulting from the introduction of residual stresses are much smaller.
Transitional Flow at the Venous Anastomosis of an Arteriovenous Graft: Potential Activation of the ERK1/2 Mechanotransduction Pathway
Authors: Loth Francis , Fischer Paul F. , Arslan Nurullah , Bertram Christopher D. , Lee Seung E. , Royston Thomas J. , Shaalan Wael E. , Bassiouny Hisham S.
Published: February 2003

We present experimental and computational results that describe the level, distribution, and importance of velocity fluctuations within the venous anastomosis of an arteriovenous graft. The motivation of this work is to understand better the importance of biomechanical forces in the development of intimal hyperplasia within these grafts. Steady-flow in vitro studies (Re=1060 and 1820) were conducted within a graft model that represents the venous anastomosis to measure velocity by means of laser Doppler anemometry. Numerical simulations with the same geometry and flow conditions were conducted by employing the spectral element technique. As flow enters the vein from the graft, the velocity field exhibits flow separation and coherent structures (weak turbulence) that originate from the separation shear layer. We also report results of a porcine animal study in which the distribution and magnitude of vein-wall vibration on the venous anastomosis were measured at the time of graft construction. Preliminary molecular biology studies indicate elevated activity levels of the extracellular regulatory kinase ERK1/2, a mitogen-activated protein kinase involved in mechanotransduction, at regions of increased vein-wall vibration. These findings suggest a potential relationship between the associated turbulence-induced vein-wall vibration and the development of intimal hyperplasia in arteriovenous grafts. Further research is necessary, however, in order to determine if a correlation exists and to differentiate the vibration effect from that of flow related effects.
Effects of Sulfamethizole and Amdinocillin against
Escherichia coli
Strains (with Various Susceptibilities) in an Ascending Urinary Tract Infection Mouse Model
Authors: Kerrn M. B. , Frimodt-Møller N. , Espersen F.
Published: February 2003

Resistance to antibiotics used for the treatment of urinary tract infections (UTIs) is increasing worldwide. The impact of in vitro resistance on clinical outcome in UTIs requires further study, since most studies of both humans and animals have evaluated only the efficacy of antibiotics toward bacteria susceptible in vitro. We were interested in evaluating the relationship between the in vitro antibacterial effect and the in vivo efficacy after antibiotic treatment. We simulated a natural ascending UTI by use of the ascending UTI mouse model and used
Escherichia coli
strains with various susceptibilities to amdinocillin (mecillinam) and sulfamethizole. Mice were treated for 3 days with antibiotic doses approximating human urinary tract concentrations after a standard oral dose. For a susceptible strain (MIC, 0.5 μg/ml) and a resistant strain (MIC, 128 μg/ml), respectively, there were significant reductions in bacterial counts in the urine, bladder, and kidneys after treatment with amdinocillin, whereas for a strain for which the MIC was 16 μg/ml, there was a significant reduction in bacterial counts in the kidneys only (
P
< 0.05). Treatment with sulfamethizole resulted in a significant reduction in bacterial counts in all samples from a susceptible strain (MIC, 128 μg/ml) and a resistant strain (MIC, 512 μg/ml). Infection with a
sulII
gene-positive strain (MIC, >2,048 μg/ml) could not be treated with sulfamethizole, as no effect could be demonstrated in the urine, bladder, or kidneys. For amdinocillin, there was no clear-cut relationship between the in vitro susceptibility and the in vivo outcome, while for sulfamethizole, we found a relationship between the MIC for the strain and the effect in the urinary tract.
Aminoglycoside Nephrotoxicity: Modeling, Simulation, and Control
Authors: Rougier Florent , Claude Daniel , Maurin Michel , Sedoglavic Alexandre , Ducher Michel , Corvaisier Stéphane , Jelliffe Roger , Maire Pascal
Published: February 2003

The main constraints on the administration of aminoglycosides are the risks of nephrotoxicity and ototoxicity, which can lead to acute, renal, vestibular, and auditory toxicities. In the present study we focused on nephrotoxicity. No reliable predictor of nephrotoxicity has been found to date. We have developed a deterministic model which describes the pharmacokinetic behavior of aminoglycosides (with a two-compartment model), the kinetics of aminoglycoside accumulation in the renal cortex, the effects of aminoglycosides on renal cells, the resulting effects on renal function by tubuloglomerular feedback, and the resulting effects on serum creatinine concentrations. The pharmacokinetic parameter values were estimated by use of the NPEM program. The estimated pharmacodynamic parameter values were obtained after minimization of the least-squares objective function between the measured and the calculated serum creatinine concentrations. A simulation program assessed the influences of the dosage regimens on the occurrence of nephrotoxicity. We have also demonstrated the relevancy of modeling of the circadian rhythm of the renal function. We have shown the ability of the model to fit with 49 observed serum creatinine concentrations for a group of eight patients treated for endocarditis by comparison with 49 calculated serum creatinine concentrations (r2= 0.988;P< 0.001). We have found that for the same daily dose, the nephrotoxicity observed with a thrice-daily administration schedule appears more rapidly, induces a greater decrease in renal function, and is more prolonged than those that occur with less frequent administration schedules (for example, once-daily administration). Moreover, for once-daily administration, we have demonstrated that the time of day of administration can influence the incidence of aminoglycoside nephrotoxicity. The lowest level of nephrotoxicity was observed when aminoglycosides were administered at 1:30 p.m. Clinical application of this model might make it possible to adjust aminoglycoside dosage regimens by taking into account both the efficacies and toxicities of the drugs.
Effects of an Efflux Mechanism and Ribosomal Mutations on Macrolide Susceptibility of
Haemophilus influenzae
Clinical Isolates
Authors: Peric Mihaela , Bozdogan Bülent , Jacobs Michael R. , Appelbaum Peter C.
Published: February 2003

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
.
Mutant Prevention Concentration of Garenoxacin (BMS-284756) for Ciprofloxacin-Susceptible or -Resistant
Staphylococcus aureus
Authors: Zhao Xilin , Eisner William , Perl-Rosenthal Nathan , Kreiswirth Barry , Drlica Karl
Published: February 2003

The new quinolone garenoxacin (BMS-284756), which lacks a C-6 fluorine, was examined for its ability to block the growth of
Staphylococcus aureus
. Measurement of the MIC and the mutant prevention concentration (MPC) revealed that garenoxacin was 20-fold more potent than ciprofloxacin for a variety of ciprofloxacin-susceptible isolates, some of which were resistant to methicillin. The MPC for 90% of the isolates (MPC
90
) was below published serum drug concentrations achieved with recommended doses of garenoxacin. These in vitro observations suggest that garenoxacin has a low propensity for selective enrichment of fluoroquinolone-resistant mutants among ciprofloxacin-susceptible isolates of
S. aureus
. For ciprofloxacin-resistant isolates, the MIC at which 90% of the isolates tested were inhibited was below serum drug concentrations while the MPC
90
was not. Thus, for these strains, garenoxacin concentrations are expected to fall inside the mutant selection window (between the MIC and the MPC) for much of the treatment time. As a result, garenoxacin is expected to selectively enrich mutants with even lower susceptibility.
Transcriptional Induction of the Penicillin-Binding Protein 2 Gene in
Staphylococcus aureus
by Cell Wall-Active Antibiotics Oxacillin and Vancomycin
Authors: Boyle-Vavra Susan , Yin Shaohui , Challapalli Mamatha , Daum Robert S.
Published: February 2003

We found an increased abundance of
pbpB
-specific transcripts in vancomycin intermediate-resistant
Staphylococcus aureus
(VISA) isolates compared with that found in paired, genetically identical, susceptible isolates. This difference in expression cannot be explained by differences in the
pbpB
promoter sequence. Since the factors controlling
pbpB
gene expression have remained largely unexplored, various conditions that might affect
pbpB
transcript abundance were examined. In both vancomycin-susceptible and VISA strains,
pbpB
expression varied with the growth phase, with the highest abundance of
pbpB
-specific transcripts detected during mid-log phase. Interestingly, both vancomycin and oxacillin were able to induce
pbpB
transcription above a constitutive level. When vancomycin was absent, one of the three
pbpB
-specific transcripts that were usually faintly detected in non-VISA strains was more readily detected in VISA strains during mid-log but not stationary phase. This transcript was enhanced in non-VISA strains by vancomycin induction. Gel shift assays indicated that an increased amount of the putative transcription factor that binds to both P1 and P1′ promoter regions is present in the cytosol of vancomycin-induced cells. Neither the SigB sigma factor nor the quorum-sensing
agr
locus was required for growth phase-variable
pbpB
expression or transcriptional induction of
pbpB
by vancomycin or oxacillin. Also, MecI, MecR1, BlaI, and BlaR1, regulatory proteins that mediate β-lactam-inducible expression of
mecA
and β-lactamase, were not required for antibiotic induction of
pbpB
transcription. These data support the idea that
pbpB
expression is modulated by a
trans
-acting factor in response to the presence of the cell wall-active antibiotics vancomycin and oxacillin.
Active-Site Residues of
Escherichia coli
DNA Gyrase Required in Coupling ATP Hydrolysis to DNA Supercoiling and Amino Acid Substitutions Leading to Novobiocin Resistance
Authors: Gross Christian H. , Parsons Jonathan D. , Grossman Trudy H. , Charifson Paul S. , Bellon Steven , Jernee James , Dwyer Maureen , Chambers Stephen P. , Markland William , Botfield Martyn , Raybuck Scott A.
Published: February 2003

DNA gyrase is a bacterial type II topoisomerase which couples the free energy of ATP hydrolysis to the introduction of negative supercoils into DNA. Amino acids in proximity to bound nonhydrolyzable ATP analog (AMP · PNP) or novobiocin in the gyrase B (GyrB) subunit crystal structures were examined for their roles in enzyme function and novobiocin resistance by site-directed mutagenesis. Purified
Escherichia coli
GyrB mutant proteins were complexed with the gyrase A subunit to form the functional A
2
B
2
gyrase enzyme. Mutant proteins with alanine substitutions at residues E42, N46, E50, D73, R76, G77, and I78 had reduced or no detectable ATPase activity, indicating a role for these residues in ATP hydrolysis. Interestingly, GyrB proteins with P79A and K103A substitutions retained significant levels of ATPase activity yet demonstrated no DNA supercoiling activity, even with 40-fold more enzyme than the wild-type enzyme, suggesting that these amino acid side chains have a role in the coupling of the two activities. All enzymes relaxed supercoiled DNA to the same extent as the wild-type enzyme did, implying that only ATP-dependent reactions were affected. Mutant genes were examined in vivo for their abilities to complement a temperature-sensitive
E. coli gyrB
mutant, and the activities correlated well with the in vitro activities. We show that the known R136 novobiocin resistance mutations bestow a significant loss of inhibitor potency in the ATPase assay. Four new residues (D73, G77, I78, and T165) that, when changed to the appropriate amino acid, result in both significant levels of novobiocin resistance and maintain in vivo function were identified in
E. coli
.
Influence of P-Glycoprotein Inhibitors on Accumulationof Macrolides in J774 MurineMacrophages
Authors: Seral Cristina , Michot Jean-Michel , Chanteux Hugues , Mingeot-Leclercq Marie-Paule , Tulkens Paul M. , Van Bambeke Françoise
Published: February 2003

The influence of inhibitors of P-glycoprotein (verapamil [VE], cyclosporine [CY], and GF120918 [GF]) on the cell handling of macrolides (erythromycin [ERY], clarithromycin [CLR], roxithromycin [ROX], azithromycin [AZM], and telithromycin [TEL]) was examined in J774 murine macrophages. The net influx rates of AZM and TEL were increased from 2- to 3.5-fold in the presence of these inhibitors, but their efflux was slowed only marginally. At 3 h, the inhibitors increased the levels of AZM, ERY, and TEL accumulation approximately three- to fourfold (the effect of VE, however, was lower) but did not influence CLR accumulation (the inhibitors had an intermediate behavior on ROX accumulation). The effect was concentration dependent (half-maximal increases in the level of accumulation of AZM were obtained with GF, CY, and VE at 0.5, 5, and 10μ M, respectively). ATP depletion also caused an approximately threefold increase in the level of accumulation of AZM. Two inhibitors of MRP (probenecid [2.5 mM] and gemfibrozil [0.25 mM]) had no effect. Monensin (a proton ionophore) completely suppressed the accumulation of AZM in control cells as well as in cells incubated in the presence of VE, demonstrating that transmembrane proton gradients are the driving force causing the accumulation of AZM in both cases. Yet, VE did not alter the pH of the lysosomes (approximately 5) or of the cytosol (approximately 7.1). P-glycoprotein was detected by immunostaining at the cell surface as well as in intracellular vacuoles (endosomes and lysosomes). The data suggest that the influx of AZM, ERY, TEL, and ROX is adversely influenced by the activity of P-glycoprotein in J774 macrophages, resulting in suboptimal drug accumulation.
Structure-Based Design and Engineering of a Nontoxic Recombinant Pokeweed Antiviral Protein with Potent Anti-Human Immunodeficiency Virus Activity
Authors: Uckun Fatih M. , Rajamohan Francis , Pendergrass Sharon , Ozer Zahide , Waurzyniak Barbara , Mao Chen
Published: February 2003

A molecular model of pokeweed antiviral protein (PAP)-RNA interactions was used to rationally engineer FLP-102(151AA152) and FLP-105(191AA192) as nontoxic PAPs with potent anti-human immunodeficiency virus (anti-HIV) activities. FLP-102 and FLP-105 have been produced inEscherichia coliand tested both in vitro and in vivo. These proteins depurinate HIV type 1 (HIV-1) RNA much better than rRNA and are more potent anti-HIV agents than native PAP or recombinant wild-type PAP. They are substantially less toxic than native PAP in BALB/c mice and exhibit potent in vivo activities against genotypically and phenotypically nucleoside reverse transcriptase inhibitor-resistant HIV-1 in a surrogate human peripheral blood lymphocyte (Hu-PBL) SCID mouse model of human AIDS. Rationally engineered nontoxic recombinant PAPs such as FLP-102 and FLP-105 may provide the basis for effective salvage therapies for patients harboring highly drug-resistant strains of HIV-1. The documented in vitro potencies of FLP-102 and FLP-105, their in vivo antiretroviral activities in the HIV-infected Hu-PBL SCID mouse model, and their favorable toxicity profiles in BALB/c mice warrant the further development of these promising new biotherapeutic agents.
Amino Acid Sequence Requirements at Residues 69 and 238 for the SME-1 β-Lactamase To Confer Resistance to β-Lactam Antibiotics
Authors: Majiduddin Fahd K. , Palzkill Timothy
Published: February 2003

Carbapenem antibiotics have been used to counteract resistant strains of bacteria harboring β-lactamases and extended-spectrum β-lactamases. Four enzymes from the class A group of β-lactamases, NMC-A, IMI-1, SME-1
,
and KPC-1, efficiently hydrolyze carbapenem antibiotics. Sequence comparisons and structural information indicate that cysteines at amino acid residues 69 and 238, which are conserved in all four of these enzymes, form a disulfide bond that is unique to these β-lactamases. To test whether this disulfide bond is required for catalytic activity, the codons for residues Cys69 and Cys238 were randomized individually and simultaneously by PCR-based mutagenesis to create random replacement libraries for these positions. Mutants that were able to confer resistance to ampicillin, imipenem, or cefotaxime were selected from these libraries. The results indicate that positions Cys69 and Cys238 are critical for hydrolysis of all of the antibiotics tested, suggesting that the disulfide bond is generally required for this enzyme to catalyze the hydrolysis of β-lactam antibiotics.
In Vitro Activities of Caspofungin Compared with Those of Fluconazole and Itraconazole against 3,959 Clinical Isolates of
Candida
spp., Including 157 Fluconazole-Resistant Isolates
Authors: Pfaller M. A. , Diekema D. J. , Messer S. A. , Hollis R. J. , Jones R. N.
Published: February 2003

Caspofungin is an echinocandin antifungal agent with broad-spectrum activity against
Candida
and
Aspergillus
spp. The in vitro activities of caspofungin against 3,959 isolates of
Candida
spp. obtained from over 95 different medical centers worldwide were compared with those of fluconazole and itraconazole. The MICs of the antifungal drugs were determined by broth microdilution tests performed according to the NCCLS method using RPMI 1640 as the test medium. Caspofungin was very active against
Candida
spp. (MIC at which 90% of the isolates were inhibited [MIC
90
], 1 μg/ml; 96% of MICs were ≤2 μg/ml).
Candida albicans
,
C. dubliniensis
,
C. tropicalis
, and
C. glabrata
were the most susceptible species of
Candida
(MIC
90
, 0.25 to 0.5 μg/ml), and
C. guilliermondii
was the least susceptible (MIC
90
, >8 μg/ml). Caspofungin was very active against
Candida
spp., exhibiting high-level resistance to fluconazole and itraconazole (99% of MICs were ≤1 μg/ml). These results provide further evidence for the spectrum and potency of caspofungin activity against a large and geographically diverse collection of clinically important isolates of
Candida
spp.
High-Dose, Short-Duration, Early Valacyclovir Therapy for Episodic Treatment of Cold Sores: Results of Two Randomized, Placebo-Controlled, Multicenter Studies
Authors: Spruance Spotswood L. , Jones Terry M. , Blatter Mark M. , Vargas-Cortes Mauricio , Barber Judy , Hill Joanne , Goldstein Donna , Schultz Margaret
Published: February 2003

Oral valacyclovir is better absorbed than oral acyclovir, increasing acyclovir bioavailability three- to fivefold. This provides the opportunity to explore whether high systemic acyclovir concentrations are effective in the treatment of cold sores (herpes labialis). Two randomized, double-blind, placebo-controlled studies were conducted. Subjects were provided with 2 g of valacyclovir twice daily for 1 day (1-day treatment), 2 g of valacyclovir twice daily for 1 day and then 1 g of valacyclovir twice daily for 1 day (2-day treatment), or a matching placebo and instructed to initiate treatment upon the first symptoms of a cold sore. In study 1, the median duration of the episode (primary endpoint) was reduced by 1.0 day (
P
= 0.001) with 1-day treatment and 0.5 days (
P
= 0.009) with 2-day treatment compared to placebo. Similarly, the mean duration of the episode was statistically significantly reduced by 1.1 days with 1-day treatment and 0.7 days with 2-day treatment compared to placebo. The proportion of subjects in whom cold sore lesion development was prevented and/or blocked was increased by 6.4% (
P
= 0.096) with 1-day treatment and 8.5% (
P
= 0.061) with 2-day treatment compared to placebo. The time to lesion healing and time to cessation of pain and/or discomfort were statistically significantly reduced with valacyclovir compared to placebo. In study 2, results similar to those in study 1 were obtained. AEs were similar across treatment groups. These studies provide evidence supporting a simple, 1-day valacyclovir treatment regimen for cold sores that is safe and effective. The 1-day valacyclovir regimen offers patients a unique and convenient dosing alternative compared to available topical therapies.
Use of the Microbial Growth Curve in Postantibiotic Effect Studies of
Legionella pneumophila
Authors: Smith Raymond P. , Baltch Aldona L. , Michelsen Phyllis B. , Ritz William J. , Alteri Richard
Published: February 2003

Using the standard Craig and Gudmundsson method (W. A. Craig and S. Gudmundsson, p. 296-329,
in
V. Lorian, ed.,
Antibiotics in Laboratory Medicine
, 1996) as a guideline for determination of postantibiotic effects (PAE), we studied a large series of growth curves for two strains of
Legionella pneumophila
. We found that the intensity of the PAE was best determined by using a statistically fitted line over hours 3 to 9 following antibiotic removal. We further determined the PAE duration by using a series of observations of the assay interval from hours 3 to 24. We determined that inoculum reduction was not necessarily the only predictor of the PAE but that the PAE was subject to the type and dose of the drug used in the study. In addition, there was a variation between strains. Only levofloxacin at five and ten times the minimum inhibitory concentration (MIC) resulted in a PAE duration of 4 to 10 h for both strains of
L. pneumophila
tested. Ciprofloxacin at five and ten times the MIC and azithromycin at ten times the MIC caused a PAE for one strain only. No PAE could be demonstrated for either strain with erythromycin or doxycycline. Using the presently described method of measuring PAE for
L. pneumophila
, we were able to detect differences in PAE which were dependent upon the
L. pneumophila
strain, the antibiotic tested, and the antibiotic concentration. We suggest the use of mathematically fitted curves for comparison of bacterial growth in order to measure PAE for
L. pneumophila
.
Activities of Moxifloxacin against, and Emergence of Resistance in,
Streptococcus pneumoniae
and
Pseudomonas aeruginosa
in an In Vitro Pharmacokinetic Model
Authors: MacGowan Alasdair P. , Rogers Chris A. , Holt H. Alan , Bowker Karen E.
Published: February 2003

The pharmacodynamics of moxifloxacin against
Streptococcus pneumoniae
and
Pseudomonas aeruginosa
were investigated in a pharmacokinetic infection model. Three strains of
S. pneumoniae
, moxifloxacin, and two strains of
P. aeruginosa
were used. Antibacterial effect and emergence of resistance were measured for both species over a 72-h period using an initial inoculum of about 10
8
CFU/ml. At equivalent area under the curve (AUC)/MIC ratios,
S. pneumoniae
was cleared from the model while
P. aeruginosa
was not. For
S. pneumoniae
, the area under the bacterial kill curve up to 72 h could be related to AUC/MIC ratio using an inhibitory maximum effect (
E
max
) model (concentration required for 50%
E
max
[EC
50
], 45 ± 22;
r
2
, 0.97). For
P. aeruginosa
even at the highest AUC/MIC ratio (427), bacterial clearance was insufficient for the EC
50
to be calculated. Emergence of resistance occurred with
P. aeruginosa
but not to any significant extent with
S. pneumoniae
. Emergence of resistance in
P. aeruginosa
as measured by population analysis profile (PAP-AUC) was dependent on drug exposure and time of exposure. In weighted least-squares regression analysis AUC/MIC ratio was predictive of PAP-AUC. When emergence of resistance was measured by the time for the colony counts on media containing antibiotic to increase by 2 logs, again AUC/MIC was the best predictor of emergence of resistance. However, for both experiments using
S. pneumoniae
and
P. aeruginosa
the correlation between all the pharmacodynamic parameters was high. These data indicate that for a given fluoroquinolone the magnitude of the AUC/MIC ratio for antibacterial effect is dependent on the bacterial species. Emergence of resistance is dependent on (i) species, (ii) duration of drug exposure, and (iii) drug exposure. A single AUC/MIC ratio magnitude is not adequate to predict antibacterial effect or emergence of resistance for all bacterial species.
Mechanism of Fluoroquinolone Resistance Is an Important Factor in Determining the Antimicrobial Effect of Gemifloxacin against
Streptococcus pneumoniae
in an In Vitro Pharmacokinetic Model
Authors: MacGowan Alasdair P. , Bowker Karen E.
Published: February 2003

Antibacterial effect and emergence of resistance to gemifloxacin and levofloxacin were studied in an in vitro pharmacokinetic model of infection. A panel of
Streptococcus pneumoniae
strains with known mechanisms of resistance were used; two strains had no known resistance mechanism, two had efflux pumps, three had
gyrA
plus
parC
mutations, and one had only a
parC
mutation. Gemifloxacin MICs were in the range of 0.016 to 0.25 mg/liter, and levofloxacin MICs ranged from 1 to 16 mg/liter. Antimicrobial effect was measured by area under the bacterial-kill curve up to 72 h, and emergence of resistance was determined by population analysis profile before and during drug exposure. The area under the curve (AUC)/MIC ratios for gemifloxacin and levofloxacin were 35 to 544 and 3 to 48, respectively. As expected on the basis of these AUC/MIC ratio differences, antibacterial effect was much greater for gemifloxacin than levofloxacin. In the gemifloxacin simulations, mechanism of resistance as well as MIC determined the antibacterial effect, as indicated by gemifloxacin’s greater effect against efflux strains compared to those with
gyrA
or
parC
mutations despite similar MICs. This was not true of levofloxacin. Emergence of resistance was not easily demonstrated with either agent, and mechanism of resistance did not have any impact on it.
Aminoglycoside Efflux in
Pseudomonas aeruginosa
: Involvement of Novel Outer Membrane Proteins
Authors: Jo James T. H. , Brinkman Fiona S. L. , Hancock Robert E. W.
Published: February 2003

The expression of tripartite multidrug efflux pumps such as MexA-MexB-OprM in
Pseudomonas aeruginosa
contributes to intrinsic resistance to a wide variety of antimicrobials, including β-lactams, chloramphenicol, macrolides, quinolones, and tetracycline. The MexX-MexY linker-pump combination has been shown to be involved in intrinsic resistance to aminoglycosides, but the identity of the cognate outer membrane channel component remains under debate. Fourteen uncharacterized OprM homologs identified in the genome of
P. aeruginosa
were examined as candidates for this role by assessing the minimum inhibitory concentrations (MICs) of aminoglycosides in
P. aeruginosa
strain PAK knockout mutants lacking the corresponding genes. Insertional inactivation of OpmG, OpmI, and OpmH resulted in decreases of various degrees in the MICs of streptomycin, kanamycin, and gentamicin. When reintroduced into
P. aeruginosa
on multicopy plasmids, OpmG was able to complement the susceptibility of an
opmG
::miniTn
5
mutant; however, cloned
opmH
, the proposed ortholog of
Escherichia coli tolC
according to our phylogenetic analysis, was able to only partially complement the
opmH
::miniTn
5
mutant. Mini-microarray hybridization analysis demonstrated that
opmG
disruption does not affect expression of OpmI or OpmH (ruling out such indirect effects on aminoglycoside resistance); however,
opmH
disruption did have possible effects on expression of OpmG and OpmI. Based on the data, we propose that OpmG is a major outer membrane efflux channel involved in aminoglycoside efflux in
P. aeruginosa
PAK and that OpmI, its most related paralog, may share an overlapping function.
Erythromycin and Clindamycin Resistance and Telithromycin Susceptibility in
Streptococcus agalactiae
Authors: Betriu C. , Culebras E. , Gómez M. , Rodríguez-Avial I. , Sánchez B. A. , Ágreda M. C. , Picazo J. J.
Published: February 2003

The rates of resistance to erythromycin and clindamycin among
Streptococcus agalactiae
strains isolated in our hospital increased from 4.2 and 0.8% in 1993 to 17.4 and 12.1%, respectively, in 2001. Erythromycin resistance was mainly due to the presence of an Erm(B) methylase, while the M phenotype was detected in 3.8% of the strains. Telithromycin was very active against erythromycin-resistant strains, irrespective of their mechanisms of macrolide resistance.
Mercury Resistance Determinants Related to Tn
21
, Tn
1696
, and Tn
5053
in Enterobacteria from the Preantibiotic Era
Authors: Essa Ashraf M. M. , Julian Daniel J. , Kidd Stephen P. , Brown Nigel L. , Hobman Jon L.
Published: February 2003

Three
mer
transposons from the Murray collection of preantibiotic enterobacteria show >99% sequence identity to current isolates. Tn
5073
is most closely related to Tn
5036
and Tn
1696
, and Tn
5074
is most closely related to Tn
5053
. Tn
5075
is most closely related to Tn
21
but lacks integron In2 and is flanked by insertion elements.
A Point Mutation in the 14α-Sterol Demethylase Gene
cyp51A
Contributes to Itraconazole Resistance in
Aspergillus fumigatus
Authors: Diaz-Guerra T. M. , Mellado E. , Cuenca-Estrella M. , Rodriguez-Tudela J. L.
Published: February 2003

The genes encoding 14α-sterol demethylases (
cyp51A
and
cyp51B
) were analyzed in 12 itraconazole (ITC)-resistant and three ITC-susceptible clinical isolates of
Aspergillus fumigatus
. Six ITC-resistant strains exhibited a substitution of another amino acid for glycine at position 54, which is located at a very conserved region of the Cyp51A protein. The
cyp51A
gene from the
A. fumigatus
wild-type strain (CM-237) was replaced with the mutated
cyp51A
gene copy of an ITC-resistant strain (AF-72). Two transformants exhibited resistance to ITC, both of which had incorporated the mutated copy of the
cyp51A
gene.
PCR-Restriction Fragment Length Polymorphism Analysis for Detection of Point Mutations Associated with Macrolide Resistance in
Campylobacter
spp
Authors: Vacher Sylvie , Ménard Armelle , Bernard Elisabeth , Mégraud Francis
Published: February 2003

A 23S rRNA gene fragment in domain V was sequenced from 30 clinical isolates of
Campylobacter
spp., including 22 resistant to macrolides. Two point mutations associated with erythromycin resistance were identified at positions 2074 and 2075 on the 23S rRNA gene (homologous to A2142C and A2143G mutations in
Helicobacter pylori
) in which an adenine residue is also replaced with a cytosine and a guanine residue, respectively. A combined PCR-restriction fragment length polymorphism technique was developed to detect these mutations by using the
Bsa
I and
Bce
AI enzymes.
ABT-773: Pharmacokinetics and Interactions with Ranitidine and Sucralfate
Authors: Pletz M. W. , Preechachatchaval V. , Bulitta J. , Allewelt M. , Burkhardt O. , Lode H.
Published: February 2003

We assessed the pharmacokinetics and interaction of ABT-773 in 12 volunteers receiving ABT-773 alone or concomitantly with ranitidine or sucralfate. Data for 150 mg of ABT-773 were as follows: the maximum concentration of the drug in plasma (
C
max
) was 318 ng/ml, its half-life was 5.66 h, and its area under the plasma concentration-time curve from 0 h to ∞ (AUC
0-∞
) was 1,662 ng · h/ml. Coadministration of ranitidine, reduced the
C
max
(−25.7%) and AUC
0-∞
(−15.8%) significantly. Sucralfate had no impact on the bioavailability of ABT-773.
In Vitro Bactericidal Activities of ABT-773 against
ermB
Strains of
Streptococcus pneumoniae
Authors: Neuhauser Melinda M. , Prause Jennifer L. , Danziger Larry H. , Pendland Susan L.
Published: February 2003

The bactericidal activities of ABT-773, a new ketolide, were compared to those of cefuroxime and amoxicillin-clavulanate against 10 strains of
Streptococcus pneumoniae
containing the
ermB
gene. MICs and time-kill curves were determined in duplicate per NCCLS guidelines with cation-adjusted Mueller-Hinton broth with 3% lysed horse blood. Viable counts were done at 0, 2, 6, and 24 h. Antibiotic concentrations tested were two and eight times the MIC. ABT-773 MICs ranged from 0.008 to 1.0 μg/ml. Bactericidal activity was observed with ABT-773 at eight times the MIC against 4 of 10 strains at 24 h compared to 10 of 10 strains with the beta-lactam antibiotics.
In Vitro Activities of Rifamycin Derivatives ABI-1648 (Rifalazil, KRM-1648), ABI-1657, and ABI-1131 against
Chlamydia trachomatis
and Recent Clinical Isolates of
Chlamydia pneumoniae
Authors: Roblin Patricia M. , Reznik Tamara , Kutlin Andrei , Hammerschlag Margaret R.
Published: February 2003

ABI-1648 (rifalazil) is a semisynthetic rifamycin with potent bactericidal activity against intracellular respiratory bacteria, including
Mycobacterium tuberculosis
, and a long half-life (∼60 h) and thus can be administered once weekly. We therefore tested the in vitro activities of ABI-1648, its derivatives ABI-1657 and ABI-1131, azithromycin, and levofloxacin against 10 strains of
Chlamydia trachomatis
and 10 recent clinical isolates of
Chlamydia pneumoniae
. The MICs at which 90% of the isolates were inhibited and the minimal bactericidal concentration at which 90% of the isolates were killed for ABI-1648, ABI-1657, and ABI-1131 were 0.0025 μg/ml for
C. trachomatis
and 0.00125 to 0.0025 μg/ml for
C. pneumoniae
. ABI-1648, ABI-1657, and ABI-1131 were 10- to 1,000-fold more active than azithromycin and levofloxacin.
In Vitro Susceptibilities of
Shigella flexneri
and
Streptococcus pyogenes
to Inner Gel of
Aloe barbadensis
Miller
Authors: Ferro Valerie A. , Bradbury Fiona , Cameron Pamela , Shakir Eisin , Rahman Sabita R. , Stimson William H.
Published: February 2003

Aloe barbadensis
Miller (or
Aloe vera
) has widespread use in health products, and despite numerous reports on the whole plant, little work has been performed on the inner gel, which has been used extensively in these products. This report describes the in vitro susceptibilities of two bacteria to this component.
Postantibiotic Effects of Garenoxacin (BMS-284756) against 12 Gram-Positive or -Negative Organisms
Authors: Pankuch G. A. , Jacobs M. R. , Appelbaum P. C.
Published: February 2003

Conventional in vitro methods were used to determine the postantibiotic effects (PAEs), sub-MIC effects (SMEs), and postantibiotic sub-MIC effects (PA-SMEs) of garenoxacin for a range of organisms. The mean PAEs of garenoxacin for pneumococci, staphylococci, and enterococci were 0.3 to 2.2 h. For
Escherichia coli
and
Pseudomonas aeruginosa
, the PAEs were 0.9 to 1.6 h. The mean PA-SMEs (0.4 times the MIC) for pneumococci, staphylococci, and enterococci were 3.0 to >10 h, 1.8 to >10.7 h, and 5.8 h, respectively, while those for
E. coli
and
P. aeruginosa
were 7.6 and 4.4 h, respectively.
Antianaerobe Activity of RBX 7644 (Ranbezolid), a New Oxazolidinone, Compared with Those of Eight Other Agents
Authors: Ednie Lois M. , Rattan Ashok , Jacobs Michael R. , Appelbaum P. C.
Published: February 2003

The activity of ranbezolid (RBX 7644), a new oxazolidinone, against 306 anaerobes was compared with those of 11 other agents. The MICs at which 50% of the isolates tested are inhibited and those at which 90% of the isolates tested are inhibited (in micrograms per milliliter) were as follows: ranbezolid, 0.03 and 0.5; linezolid, 2 and 4; vancomycin, >16 and >16; teicoplanin, 1 and >16; quinupristin-dalfopristin, 1 and >8; amoxicillin-clavulanate, 0.5 and 2; imipenem, 0.125 and 1; clindamycin, 0.25 and 8; metronidazole, 1 and 4; gatifloxacin, 0.5 and 4; and moxifloxacin, 0.5 and 2, respectively. Ranbezolid had very good in vitro activity against both gram-negative and -positive anaerobes.
Antipneumococcal and Antistaphylococcal Activities of Ranbezolid (RBX 7644), a New Oxazolidinone, Compared to Those of Other Agents
Authors: Hoellman Dianne B. , Lin Gengrong , Ednie Lois M. , Rattan Ashok , Jacobs Michael R. , Appelbaum Peter C.
Published: February 2003

For 260 pneumococcal and 266 staphylococcal strains, ranbezolid MICs ranged from ≤0.06 to 4 μg/ml. The MICs for pneumococci were similar irrespective of the strains' β-lactam, macrolide, or quinolone susceptibilities, and ranbezolid MICs for coagulase-negative staphylococci were lower than those for
Staphylococcus aureus
. Ranbezolid was bacteriostatic against pneumococci. Ranbezolid MICs were similar to or lower than those of linezolid. Vancomycin and quinupristin-dalfopristin were also very active.
Lack of Synergy of Erythromycin Combined with Penicillin or Cefotaxime against
Streptococcus pneumoniae
In Vitro
Authors: Lin Eugene , Stanek Ronald J. , Mufson Maurice A.
Published: February 2003

We investigated a possible synergistic effect of a macrolide and β-lactams against
Streptococcus pneumoniae
strains with different resistance profiles. Checkerboard and time-kill assays of erythromycin combined with penicillin or cefotaxime essentially showed indifference, suggesting that these antibiotics in combinations in vitro act substantially as individuals in their activity against
S. pneumoniae
.
Vancomycin Resistance Is Maintained in Enterococci in the Viable but Nonculturable State and after Division Is Resumed
Authors: Lleò Maria del Mar , Bonato Barbara , Signoretto Caterina , Canepari Pietro
Published: February 2003

Stressed vancomycin-resistant enterococci (VRE) can activate a survival strategy known as the viable but nonculturable (VBNC) state and are able to maintain vancomycin resistance. During restoration of division they continue to express the vancomycin resistance trait. We suggest that VBNC enterococci may constitute further reservoirs of VRE and therefore represent an additional risk for human health.