bluuebunny/crossref_metadata_2025 huggingface dataset:
Real-Time Direct Position Analysis of Parallel Spherical Wrists by Using Extra Sensors
Authors: Vertechy R. , Parenti-Castelli V.
Published: December 2005

The paper presents an algorithm for the real-time evaluation of the actual end-effector orientation of general parallel spherical wrists. Conceptually, the method relies on evidence that the pose of a rigid body is defined once the location of at least two linearly independent vectors attached to the body is known. The location of these vectors of the wrist end-effector is determined by the solution of the direct position analysis of some properly chosen kinematic chains (legs) of the manipulator. In order to accomplish this analysis, extra sensors, which measure suitable non-actuated variables of the chosen legs, need to be placed in addition to the ones normally embedded in the servomotors, i.e., the sensors which measure the actuated variables. From a mathematical point of view, the algorithm is built on the polar decomposition of a matrix and has inherent least square features. Thus, together with measurement redundancy, i.e., more sensors (extra sensors) than the mechanism degrees of freedom, the method also makes it possible to minimize the influence of both round-off and measurement errors on the estimation of the location of the wrist end-effector. The method is general but, in order to prove its effectiveness, without loss of generality it has been customized to the solution of the 3(UPS)-S fully parallel wrist architecture (where U, P and S are for universal, prismatic and spherical joint, respectively). Comparison of the proposed method, in both its general and specialized form, with others from the literature is provided.
Contact Area as a Critical Determinant in the Tribology Of Metal-on-Polyethylene Total Joint Arthroplasty
Authors: Mazzucco Daniel , Spector Myron
Published: December 2005

The effects of contact area and contact stress on friction and wear of polyethylene-metal articulation were evaluated using a bidirectional pin-on-disk apparatus. A doubling of the contact area under fixed loading conditions led to a 50% increase in the coefficient of friction and a doubling of the wear rate. There appeared to be a relationship between the increase in wear rate and the increase in the coefficient of friction. A model was developed to explain the mechanism by which engagement of asperities results in the increasing wear rate with increasing contact area despite the decreased stress.
Impact of Mental Iteration on Concept Generation
Authors: Chusilp Pawat , Jin Yan
Published: December 2005

Mental iteration in conceptual design involves repetition of cognitive activities when designers perceive discrepancies of the desired state and current state of design. Although it is believed that mental iteration has significant impact on design process and design results, little proof has been developed and our current understanding of mental iteration is still limited. This paper presents a preliminary study of impact of mental iteration on performance of designers in conceptual design. Mental iteration is modeled as various iterative loops of cognitive activities. An experiment was carried out to study the mental iteration behavior in conceptual design. The analysis of correlation was performed to identify significant associations between design metrics and the number and frequency of different types of iterations. The results provide evidence that mental iteration has not only positive but also negative impact on design performance and different types of iteration yield different impacts.
Diffuse boundary extraction of breast masses on ultrasound by leak plugging
Authors: Cary T. W. , Conant E. F. , Arger P. H. , Sehgal C. M.
Published: December 2005

We propose a semiautomated seeded boundary extraction algorithm that delineates diffuse region boundaries by finding and plugging their leaks. The algorithm not only extracts boundaries that are partially diffuse, but in the process finds and quantifies those parts of the boundary that are diffuse, computing local sharpness measurements for possible use in computer‐aided diagnosis. The method treats a manually drawn seed region as a wellspring of pixel “fluid” that flows from the seed out towards the boundary. At indistinct or porous sections of the boundary, the growing region will leak into surrounding tissue. By changing the size of structuring elements used for growing, the algorithm changes leak properties. Since larger elements cannot leak as far from the seed, they produce compact, less detailed boundary approximations; conversely, growing from smaller elements results in less constrained boundaries with more local detail. This implementation of the leak plugging algorithm decrements the radius of structuring disks and then compares the regions grown from them as they increase in both area and boundary detail. Leaks are identified if the outflows between grown regions are large compared to the areas of the disks. The boundary is plugged by masking out leaked pixels, and the process continues until one‐pixel‐radius resolution. When tested against manual delineation on scans of 40 benign masses and 40 malignant tumors, the plugged boundaries overlapped and correlated well in area with manual tracings, with mean overlap of 0.69 and area correlation of 0.86, but the algorithm's results were more reproducible.
Simplifying the Motion of Coupled Oscillators Using the FFT
Authors: Easton Don
Published: December 2005

When two identical simple harmonic oscillators are coupled by a linear spring that has a spring constant kc, the system has two resonant frequencies. There is a resonance at their natural frequency, ω0, when the oscillators oscillate in phase and a resonance at the frequency ω = ω02 + 2kc/m when the oscillators are 180° out of phase. These oscillations are referred to individually as the symmetric and antisymmetric modes or collectively as the normal modes. The frequencies are called the normal frequencies.
Gone to Flab
Authors: Leslie Mitch
Published: December 2005

The muscles of a gym rat and a couch potato don't just look different, they work differently too. The muscles of obese people hoard fat, and a new study might explain why. The work identifies a key lipid-metabolism enzyme that cranks up in hefty individuals and spurs muscle cells to get chubby. Quelling the enzyme might help fend off obesity and diabetes.
What's Bugging You?
Authors: Leslie Mitch
Published: December 2005

Alzheimer's disease, atherosclerosis, and other diseases of aging might share something with sinus infections and flu. According to preliminary research, all stem from bacterial or viral attacks. Circumstantial evidence points to the lung-attacking bacterium
Chlamydia pneumoniae
, the herpes simplex I virus, and other germs. Although supporters of the hypothesis have amassed suggestive data, many researchers remain skeptical. However, advocates argue that we might have to accept weaker-than-usual evidence because the diseases kill so many people.
Cancer Connection
Authors: Leslie Mitch
Published: December 2005

Cancer and long life seem mutually exclusive, but a new study suggests that a life-extending enzyme also hikes tumor risk. Researchers knew that the enzyme, SIRT1, stalls a pathway that causes abnormal cells to commit suicide. The new work pinpoints a protein that normally keeps SIRT1 under control, but whose production wanes with age.
Bionic Grandma
Authors: Davenport R. John
Published: December 2005

Aging takes a toll on organs and tissues. Skin rumples, hearts fail, and muscles weaken. Drugs and other interventions can sometimes slow the devastation but rarely repair existing damage. Furthermore, although transplants can replace ruined organs, demand for donors outstrips supply, and immune rejection is a risk. To circumvent these problems, researchers are working to create tissues in the lab that can substitute for defective ones in the body. Building on previous success in designing simple tissues such as skin and bone, they are seeking new biomaterials and methods to craft more complicated ones.
Mitochondrial Genetics of Aging: Intergenomic Conflict Resolution
Authors: Rand David M.
Published: December 2005

Mitochondria are the organelles of aerobic respiration. They consume the oxygen we breathe to stay alive and generate energy for cells to function. But oxygen can be dangerous. Indeed, mitochondria generate the majority of reactive oxygen species that are prime suspects among the causes of aging. Mitochondria have been influential elements of evolving eukaryotic cells for perhaps 2 billion years, since a eubacterium fused with an archaebacterium. The picture that has emerged from this long history of genomic fusion is that of a complex network of nuclear-mitochondrial cross-talk. Here, we discuss the biochemical and genetic conflicts between mitochondria and nucleus, which have shaped the role of mitochondria in aging, and point to new paths for further investigations.
A Switch in Time Saves Mind
Authors: Leslie Mitch
Published: December 2005

If we have a choice, most of us would prefer to grow old like newsman Mike Wallace, who at 87 is still sticking it to shifty politicians and louche lawyers on the television program
60 Minutes
. A new study identifies a mechanism that allows gracefully aging rodents to maintain their memories. The results might help researchers design treatments to stave off age-related mental decline.
Immune Shaping and the Development of Alzheimer's Disease Vaccines
Authors: Federoff Howard J. , Bowers William J.
Published: December 2005

Given the emotional, social, and financial devastation wrought by Alzheimer's disease (AD), it is imperative that effective therapeutics be devised to ameliorate this presently incurable disorder. Vaccine-based approaches have been developed to target and eliminate amyloid beta (Aβ), a key peptide implicated in AD pathogenesis. Preclinical successes in AD mouse models created excitement and impetus for the clinical application of an Aβ-based vaccine. Eliciting immune responses against a self-peptide (that is, a peptide produced by the organism itself), such as Aβ, carries with it the potential to induce autoimmune and inflammatory conditions in the vaccinated individual, a caveat borne out in multiple patients enrolled as part of a recent clinical trial. These clinical adverse events seemingly overshadowed interesting behavioral stabilization and alterations of Aβ burden in these and other vaccinated patients, thus speaking to the potential of immunotherapy for AD. Understanding the mechanisms by which vaccines reduce Aβ burden in AD brain and the types of immune responses raised, as well as developing new modalities of vaccine delivery that facilitate the modulation of elicited immune responses, will undoubtedly lead to a new generation of efficacious Aβ immunotherapeutics with improved safety profiles.
Oxidants off the Hook?
Authors: Leslie Mitch
Published: December 2005

A new study of rapidly aging mice might tarnish the idea that oxidants foster aging. The rodents deteriorate despite having normal quantities of the destructive molecules. The work implicates mitochondrial slowdown in the animals' demise. However, some researchers question the results.
When T Cells Get Old
Authors: Pawelec Graham
Published: December 2005

Why is vaccination against infectious diseases less effective in older patients than in younger ones? Why do the elderly suffer from more frequent and severe infectious episodes than the young? The answer to both these questions is immunosenescence--the poorly defined changes that occur in the immune system as a result of the disrupted performance of multiple components of immunity. Presentations from a recent workshop, which are summarized here, examined these questions and provided some insights from the perspective of improving vaccination strategies among the elderly.
Loose Chromosomes Sink Cells
Authors: Leslie Mitch
Published: December 2005

"Just relax" might be good advice for stressed-out holiday travelers, but it could be disastrous for chromosomes, according to work presented at the American Society for Cell Biology meeting in San Francisco, California, on 13 December. The study suggests that chromosomes uncoil somewhat in patients with a disease that resembles premature aging, an alteration that could unleash genes whose products aren't needed.
A Bacterial Inhibitor of Host Programmed Cell Death Defenses Is an E3 Ubiquitin Ligase
Authors: Janjusevic Radmila , Abramovitch Robert B. , Martin Gregory B. , Stebbins C. Erec
Published: December 2005

The
Pseudomonas syringae
protein AvrPtoB is translocated into plant cells, where it inhibits immunity-associated programmed cell death (PCD). The structure of a C-terminal domain of AvrPtoB that is essential for anti-PCD activity reveals an unexpected homology to the U-box and RING-finger components of eukaryotic E3 ubiquitin ligases, and we show that AvrPtoB has ubiquitin ligase activity. Mutation of conserved residues involved in the binding of E2 ubiquitin–conjugating enzymes abolishes this activity in vitro, as well as anti-PCD activity in tomato leaves, which dramatically decreases virulence. These results show that
Pseudomonas syringae
uses a mimic of host E3 ubiquitin ligases to inactivate plant defenses.
Fermionic Superfluidity with Imbalanced Spin Populations
Authors: Zwierlein Martin W. , Schirotzek André , Schunck Christian H. , Ketterle Wolfgang
Published: December 2005

We established superfluidity in a two-state mixture of ultracold fermionic atoms with imbalanced state populations. This study relates to the long-standing debate about the nature of the superfluid state in Fermi systems. Indicators for superfluidity were condensates of fermion pairs and vortices in rotating clouds. For strong interactions, near a Feshbach resonance, superfluidity was observed for a broad range of population imbalances. We mapped out the superfluid regime as a function of interaction strength and population imbalance and characterized the quantum phase transition to the normal state, known as the Pauli limit of superfluidity.
Pairing and Phase Separation in a Polarized Fermi Gas
Authors: Partridge Guthrie B. , Li Wenhui , Kamar Ramsey I. , Liao Yean-an , Hulet Randall G.
Published: December 2005

We report the observation of pairing in a gas of atomic fermions with unequal numbers of two components. Beyond a critical polarization, the gas separates into a phase that is consistent with a superfluid paired core surrounded by a shell of normal unpaired fermions. The critical polarization diminishes with decreasing attractive interaction. For near-zero polarization, we measured the parameter β = –0.54 ± 0.05, describing the universal energy of a strongly interacting paired Fermi gas, and found good agreement with recent theory. These results are relevant to predictions of exotic new phases of quark matter and of strongly magnetized superconductors.
The Second Ring-Moon System of Uranus: Discovery and Dynamics
Authors: Showalter Mark R. , Lissauer Jack J.
Published: December 2005

Deep exposures of Uranus taken with the Hubble Space Telescope reveal two small moons and two faint rings. All of them orbit outside of Uranus's previously known (main) ring system but are interior to the large, classical moons. The outer new moon, U XXVI Mab, orbits at roughly twice the radius of the main rings and shares its orbit with a dust ring. The second moon, U XXVII Cupid, orbits just interior to the satellite Belinda. A second ring falls between the orbits of Portia and Rosalind, in a region with no known source bodies. Collectively, these constitute a densely packed, rapidly varying, and possibly unstable dynamical system.
Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK
Authors: Komeili Arash , Li Zhuo , Newman Dianne K. , Jensen Grant J.
Published: December 2005

Magnetosomes are membranous bacterial organelles sharing many features of eukaryotic organelles. Using electron cryotomography, we found that magnetosomes are invaginations of the cell membrane flanked by a network of cytoskeletal filaments. The filaments appeared to be composed of MamK, a homolog of the bacterial actin-like protein MreB, which formed filaments in vivo. In a
mamK
deletion strain, the magnetosome-associated cytoskeleton was absent and individual magnetosomes were no longer organized into chains. Thus, it seems that prokaryotes can use cytoskeletal filaments to position organelles within the cell.
Efficacy of Amphotericin B in Combination with Flucytosine against Flucytosine-Susceptible or Flucytosine-Resistant Isolates of
Cryptococcus neoformans
during Disseminated Murine Cryptococcosis
Authors: Schwarz Patrick , Dromer Françoise , Lortholary Olivier , Dannaoui Eric
Published: December 2005

Whether or not flucytosine should be administered to patients infected with
Cryptococcus neoformans
isolates found to be resistant to flucytosine in vitro remains a controversial issue. Thus, the efficacy of amphotericin B and flucytosine in combination was investigated by mortality and fungal burden studies in a murine model of disseminated cryptococcosis using two clinical isolates of
Cryptococcus neoformans
, one susceptible and one resistant (i.e., 64 μg/ml) to flucytosine. Amphotericin B was given intraperitoneally at 0.25 or 0.5 mg/kg/day, while flucytosine was given at 100 or 250 mg/kg/day orally. Treatment was started 24 h or day 6 after inoculation and continued for 5 days in fungal burden and mortality studies, respectively. The combination of amphotericin B at 0.5 mg/kg/day and flucytosine at 250 mg/kg/day was significantly more effective than monotherapies for reducing fungal burden in brain, spleen, and lungs after infection by the flucytosine-susceptible isolate and in brain and spleen for the flucytosine-resistant isolate. For the flucytosine-resistant isolate, the combination of amphotericin B at 0.5 mg/kg/day with flucytosine at 100 mg/kg/day was significantly better than monotherapies for reducing the fungal burden in the brain. Survival obtained after the combination of amphotericin B at 0.5 mg/kg/day and flucytosine at 250 mg/kg/day increased compared to that obtained with monotherapies for both isolates, but the difference was statistically significant only for the flucytosine-susceptible isolate. Antagonism was never observed. This study demonstrates the beneficial effect of the addition of flucytosine to amphotericin B against experimental disseminated cryptococcal infection even when the
C. neoformans
isolate is resistant to flucytosine.
In Vivo Efficacies and Pharmacokinetics of DX-619, a Novel Des-Fluoro(6) Quinolone, against
Streptococcus pneumoniae
in a Mouse Lung Infection Model
Authors: Fukuda Yuichi , Yanagihara Katsunori , Ohno Hideaki , Higashiyama Yasuhito , Miyazaki Yoshitsugu , Tsukamoto Kazuhiro , Hirakata Yoichi , Tomono Kazunori , Mizuta Yohei , Tashiro Takayoshi , Kohno Shigeru
Published: December 2005

DX-619 is a novel des-fluoro(6) quinolone with potent activity against gram-positive pathogens. The in vivo activity of DX-619 against
Streptococcus pneumoniae
was compared with those of fluoro(6) quinolones, sitafloxacin, and ciprofloxacin in a mouse model. Two strains of
S. pneumoniae
were used: a penicillin-sensitive
S. pneumoniae
(PSSP) strain and a penicillin-resistant
S. pneumoniae
(PRSP) strain. Furthermore, these strains showed intermediate susceptibilities to ciprofloxacin. In murine lung infections caused by PSSP, the 50% effective doses (ED
50
s) of DX-619, sitafloxacin, and ciprofloxacin were 9.15, 11.1, and 127.6 mg/kg of body weight, respectively. Against PRSP-mediated pneumonia in mice, the ED
50
s of DX-619, sitafloxacin, and ciprofloxacin were 0.69, 4.84, and 38.75 mg/kg, respectively. The mean ± standard error of the mean viable bacterial counts in murine lungs infected with PSSP and treated with DX-619, sitafloxacin, ciprofloxacin (10 mg/kg twice daily), and saline (twice daily) were 1.75 ± 0.06, 1.92 ± 0.23, 6.48 ± 0.28, and 7.57 ± 0.13 log
10
CFU/ml, respectively. Furthermore, the numbers of viable bacteria in lungs infected with PRSP and treated with the three agents and not treated (control) were 1.73 ± 0.04, 2.28 ± 0.17, 4.61 ± 0.59, and 5.54 ± 0.72 log
10
CFU/ml, respectively. DX-619 and sitafloxacin significantly decreased the numbers of viable bacteria in the lungs compared to the numbers in the lungs of ciprofloxacin-treated and untreated mice. The pharmacokinetic parameter of the area under the concentration-time curve (AUC)/MIC ratio in the lungs for DX-619, sitafloxacin, and ciprofloxacin were 171.0, 21.92, and 1.22, respectively. The AUC/MIC ratio in the lungs was significantly higher for DX-619 than for sitafloxacin and ciprofloxacin. Our results suggest that DX-619 and sitafloxacin are potent against both PSSP and PRSP in our mouse pneumonia model.
Posaconazole as Salvage Therapy for Zygomycosis
Authors: Greenberg R. N. , Mullane K. , van Burik J.-A. H. , Raad I. , Abzug M. J. , Anstead G. , Herbrecht R. , Langston A. , Marr K. A. , Schiller G. , Schuster M. , Wingard J. R. , Gonzalez C. E. , Revankar S. G. , Corcoran G. , Kryscio R. J. , Hare R.
Published: December 2005

Zygomycosis, an infection that is associated with significant morbidity and mortality, is becoming common in immunocompromised patients. Posaconazole is a new extended-spectrum azole antifungal that has demonstrated in vitro and in vivo activity against zygomycetes. This report provides the results from the first 24 patients with active zygomycosis who were enrolled in two open-label, nonrandomized, multicentered compassionate trials that evaluated oral posaconazole as salvage therapy for invasive fungal infections. Posaconazole was usually given as an oral suspension of 200 mg four times a day or 400 mg twice a day. Eleven (46%) of the infections were rhinocerebral. Duration of posaconazole therapy ranged from 8 to 1,004 days (mean, 292 days; median, 182 days). Rates of successful treatment (complete cure and partial response) were 79% in 19 subjects with zygomycosis refractory to standard therapy and 80% in 5 subjects with intolerance to standard therapy. Overall, 19 of 24 subjects (79%) survived infection. Survival was also associated with surgical resection of affected tissue and stabilization or improvement of the subjects' underlying illnesses. Failures either had worsening of underlying illnesses or requested all therapy withdrawn; none of the failures received more than 31 days of posaconazole. Posaconazole oral solution was well tolerated and was discontinued in only one subject due to a drug rash. Posaconazole appears promising as an oral therapy for zygomycosis in patients who receive required surgery and control their underlying illness.
Preliminary Mapping of a Putative Inhibitor-Binding Pocket for Human Immunodeficiency Virus Type 1 Integrase Inhibitors
Authors: Lee Deborah J. , Robinson W. Edward
Published: December 2005

Molecular modeling studies have identified a putative human immunodeficiency virus (HIV) integrase (IN) inhibitor-binding pocket for
l
-chicoric acid (
l
-CA) and other inhibitors of IN (C. A. Sotriffer, H. Ni, and A. McCammon, J. Med. Chem. 43:4109-4117, 2000). By using site-directed mutagenesis of several amino acid residues identified by modeling studies, a common inhibitor-binding pocket on IN was confirmed for
l
-CA and the diketo acid L-731,988. Specifically, the single mutations E92K, Q148A, K156A, K156R, G140S, and G149S, as well as the double mutations C65S-K156N and H67D-G140A were evaluated for their effects on enzymatic activity and inhibitor susceptibility. Each recombinant IN was attenuated for 3′-end processing and strand transfer activities. Most proteins were also attenuated for disintegration; the IN that contained K156R and C65S-K156N, however, displayed disintegration activity similar to that of IN from HIV
NL4-3
. All mutant IN proteins demonstrated decreased susceptibility to
l
-CA, while all mutant proteins except E92K and K156R demonstrated resistance to L-731,988. These data validate the computer modeling data and demonstrate that
l
-CA and L-731,988 share an overlapping inhibitor-binding pocket that involves amino acids Q148, C65, and H67. The resistance studies confirm that L-731,988 fills one-half of the inhibitor-binding pocket and binds to Q148 but excludes E92, while
l
-CA fills the entire binding groove and thus interacts with E92. These results provide “wet laboratory” evidence that molecular models of the HIV IN inhibitor-binding pocket can be used for drug discovery.
Open-Label, Randomized Comparison of Itraconazole versus Caspofungin for Prophylaxis in Patients with Hematologic Malignancies
Authors: Mattiuzzi Gloria N. , Alvarado Gladys , Giles Francis J. , Ostrosky-Zeichner Luis , Cortes Jorge , O'Brien Susan , Verstovsek Srdan , Faderl Stefan , Zhou Xian , Raad Issam I. , Bekele B. Nebiyou , Leitz G. J. , Lopez-Roman Ivonne , Estey Elihu H.
Published: December 2005

Invasive fungal infection remains the most common cause of infectious death in acute leukemia. In this open-label, randomized study, we compared the efficacy and safety of caspofungin with that of intravenous itraconazole for antifungal prophylaxis in patients undergoing induction chemotherapy for acute myelogenous leukemia or myelodysplastic syndrome. Of 200 patients, 192 were evaluable for efficacy (86 for itraconazole, 106 for caspofungin). Duration of prophylaxis (median, 21 days [range, 1 to 38 days]), demographics, and prognostic factors were similar in both groups. Ninety-nine patients completed antifungal prophylaxis without developing fungal infection (44 [51%] with itraconazole, 55 [52%] with caspofungin). Twelve patients developed documented invasive fungal infections, five in the itraconazole group (four with candidemia and one withAspergilluspneumonia), and seven in the caspofungin group (two with candidemia, two with disseminated trichosporon species, two withAspergilluspneumonia, and one with disseminatedFusariumspp). Two patients in the itraconazole group and four in the caspofungin group died of fungal infection (P= 0.57). Grade 3 to 4 adverse event rates were comparable between groups; the most common event in both was reversible hyperbilirubinemia. No evidence of cardiovascular toxicity from intravenous itraconazole was noted among patients older than 60. In conclusion, intravenous itraconazole and caspofungin provided similar protection against invasive fungal infection during induction chemotherapy, and both drugs were well tolerated.
In Vitro Activity of Moxifloxacin against 923 Anaerobes Isolated from Human Intra-Abdominal Infections
Authors: Goldstein Ellie J. C. , Citron Diane M. , Warren Yumi A. , Tyrrell Kerin L. , Merriam C. Vreni , Fernandez Helen
Published: December 2005

The in vitro activity of moxifloxacin against 923 recent anaerobic isolates obtained from pretreatment cultures in patients with complicated intra-abdominal infections was studied using the CLSI M11-A-6 agar dilution method. Moxifloxacin was active against 87% (96 of 110)
Bacteroides fragilis
strains at ≤1 μg/ml and 87% (79 of 90)
B. thetaiotaomicron
strains at ≤2 μg/ml. Species variation was seen, with
B. uniformis
,
B. vulgatus
,
Clostridium clostridioforme
, and
C. symbiosum
being least susceptible and accounting for most of the resistant isolates; excluding the aforementioned four resistant species, 86% (303 of 363) of
Bacteroides
species isolates and 94% (417 of 450) of all other genera and species were susceptible to ≤2 μg/ml of moxifloxacin. Overall, moxifloxacin was active against 763 of 923 (83%) of strains at ≤2 μg/ml, supporting its use as a monotherapy for some community-acquired intra-abdominal infections.
Tetracycline Resistance in
Escherichia coli
and Persistence in the Infantile Colonic Microbiota
Authors: Karami Nahid , Nowrouzian Forough , Adlerberth Ingegerd , Wold Agnes E.
Published: December 2005

The ecological impact of antibiotic resistance in the absence of selective pressure has been poorly studied. We assessed the carriage of tetracycline resistance genes, persistence in the microbiota, fecal population counts and virulence factor genes in 309 commensal, intestinal
Escherichia coli
strains obtained from 128 Swedish infants followed during the first year of life with regular quantitative fecal cultures. No infant was given tetracycline, but 25% received other antibiotics. Tetracycline resistance was identified in 12% of strains, all of which carried either
tet
(A) (49%) or
tet
(B) (51%) genes. Resistance to other antibiotics occurred in 50% of
tet
(A)-positive strains, 42% of
tet
(B)-positive strains and 13% of tetracycline-sensitive strains. However, colonization with tetracycline-resistant strains was unrelated to treatment with antibiotics. Strains that were
tet
(B)- or
tet
(A)-positive carried the genes for P fimbriae and aerobactin, respectively, more often than susceptible strains. Tetracycline-resistant and -susceptible strains were equally likely to persist among the intestinal microbiota for ≥3 weeks and had similar population numbers. However, when a resistant strain and a susceptible strain colonized a child simultaneously, the resistant variety showed lower counts (
P
= 0.03). In cases of long-term colonization by initially tetracycline-resistant
E. coli
strains, loss of
tet
genes occurred in 3 of 13 cases with variable effects on population counts. The results indicate that there is limited pressure against the carriage of
tet
genes in the infantile gut microbiota even in the absence of antibiotics. Resistant strains may possess colonization factors that balance the cost of producing resistance elements.
In Vitro Effects of Thiazolides on
Giardia lamblia
WB Clone C6 Cultured Axenically and in Coculture with Caco2 Cells
Authors: Müller Joachim , Rühle Géraldine , Müller Norbert , Rossignol Jean-François , Hemphill Andrew
Published: December 2005

The thiazolides represent a novel class of anti-infective drugs, with the nitrothiazole nitazoxanide [2-acetolyloxy-
N
-(5-nitro 2-thiazolyl) benzamide] (NTZ) as the parent compound. NTZ exhibits a broad spectrum of activities against a wide variety of helminths, protozoa, and enteric bacteria infecting animals and humans. In vivo, NTZ is rapidly deacetylated to tizoxanide (TIZ), which exhibits similar activities. We have here comparatively investigated the in vitro effects of NTZ, TIZ, a number of other modified thiazolides, and metronidazole (MTZ) on
Giardia lamblia
trophozoites grown under axenic culture conditions and in coculture with the human cancer colon cell line Caco2. The modifications of the thiazolides included, on one hand, the replacement of the nitro group on the thiazole ring with a bromide, and, on the other hand, the differential positioning of methyl groups on the benzene ring. Of seven compounds with a bromo instead of a nitro group, only one, RM4820, showed moderate inhibition of
Giardia
proliferation in axenic culture, but not in coculture with Caco2 cells, with a 50% inhibitory concentration (IC
50
) of 18.8 μM; in comparison, NTZ and tizoxanide had IC
50
s of 2.4 μM, and MTZ had an IC
50
of 7.8 μM. Moreover, the methylation or carboxylation of the benzene ring at position 3 resulted in a significant decrease of activity, and methylation at position 5 completely abrogated the antiparasitic effect of the nitrothiazole compound. Trophozoites treated with NTZ showed distinct lesions on the ventral disk as soon as 2 to 3 h after treatment, whereas treatment with metronidazole resulted in severe damage to the dorsal surface membrane at later time points.
Ciprofloxacin and Trimethoprim Cause Phage Induction and Virulence Modulation in
Staphylococcus aureus
Authors: Goerke Christiane , Köller Johanna , Wolz Christiane
Published: December 2005

In
Staphylococcus aureus
strains of human origin, phages which integrate into the chromosomal gene coding for β-hemolysin (
hlb
) are widely distributed. Most of them encode accessory virulence determinants such as staphylokinase (
sak
) or enterotoxins. Here, we analyzed the effects of ciprofloxacin and trimethoprim on phage induction and expression of phage-encoded virulence factors by using isolates from patients with cystic fibrosis for which the induction of
hlb
-converting phages was demonstrated in vivo (C. Goerke, S. Matias y Papenberg, S. Dasbach, K. Dietz, R. Ziebach, B. C. Kahl, and C. Wolz, J. Infect. Dis. 189:724-734, 2004) as well as a φ13 lysogen of phage-cured strain 8325-4. Treatment of lysogens with subinhibitory concentrations of either antibiotic resulted in (i) delysogenization of strains resembling the isolates picked up after chronic lung infection and (ii) replication of phages in the bacterial host in a dose-dependent manner. Ciprofloxacin treatment resulted in enhanced
recA
transcription, indicating involvement of the SOS response in phage mobilization. Induction of φ13 was linked to elevated expression of the phage-encoded virulence gene
sak
, chiefly due to the activation of latent phage promoters. In summary, we could show the induction of
hlb
-converting phages and a subsequent virulence modulation of the host bacterium by ciprofloxacin and trimethoprim.
Novel Plasmid-Mediated 16S rRNA Methylase, RmtC, Found in a
Proteus mirabilis
Isolate Demonstrating Extraordinary High-Level Resistance against Various Aminoglycosides
Authors: Wachino Jun-ichi , Yamane Kunikazu , Shibayama Keigo , Kurokawa Hiroshi , Shibata Naohiro , Suzuki Satowa , Doi Yohei , Kimura Kouji , Ike Yasuyoshi , Arakawa Yoshichika
Published: December 2005

Proteus mirabilis
ARS68, which demonstrated a very high level of resistance to various aminoglycosides, was isolated in 2003 from an inpatient in Japan. The aminoglycoside resistance of this strain could not be transferred to recipient strains
Escherichia coli
CSH-2 and
E. coli
HB101 by a general conjugation experiment, but
E. coli
DH5α was successfully transformed by electroporation with the plasmid of the parent strain, ARS68, and acquired an unusually high degree of resistance against aminoglycosides. Cloning and sequencing analyses revealed that the presence of a novel 16S rRNA methylase gene, designated
rmtC
, was responsible for resistance in strain ARS68 and its transformant. The G+C content of
rmtC
was 41.1%, and the deduced amino acid sequences of the newly identified 16S rRNA methylase, RmtC, shared a relatively low level of identity (≤29%) to other plasmid-mediated 16S rRNA methylases, RmtA, RmtB, and ArmA, which have also been identified in pathogenic gram-negative bacilli. Also, RmtC shared a low level of identity (≤28%) with the other 16S rRNA methylases found in aminoglycoside-producing actinomycetes. The purified histidine-tagged RmtC clearly showed methyltransferase activity against
E. coli
16S rRNA in vitro.
rmtC
was located downstream of an IS
Ecp1
-like element containing
tnpA
. Several plasmid-mediated 16S rRNA methylases have been identified in pathogenic gram-negative bacilli belonging to the family
Enterobacteriaceae
, and some of them are dispersing worldwide. The acceleration of aminoglycoside resistance among gram-negative bacilli by producing plasmid-mediated 16S rRNA methylases, such as RmtC, RmtB, and RmtA, may indeed become an actual clinical hazard in the near future.
Phenothiazinium Antimicrobial Photosensitizers Are Substrates of Bacterial Multidrug Resistance Pumps
Authors: Tegos George P. , Hamblin Michael R.
Published: December 2005

Antimicrobial photodynamic therapy (PDT) combines a nontoxic photoactivatable dye, or photosensitizer (PS), with harmless visible light to generate singlet oxygen and free radicals that kill microbial cells. Although the light can be focused on the diseased area, the best selectivity is achieved by choosing a PS that binds and penetrates microbial cells. Cationic phenothiazinium dyes, such as methylene blue and toluidine blue O, have been studied for many years and are the only PSs used clinically for antimicrobial PDT. Multidrug resistance pumps (MDRs) are membrane-localized proteins that pump drugs out of cells and have been identified for a wide range of organisms. We asked whether phenothiazinium salts with structures that are amphipathic cations could potentially be substrates of MDRs. We used MDR-deficient mutants of
Staphylococcus aureus
(NorA),
Escherichia coli
(TolC), and
Pseudomonas aeruginosa
(MexAB) and found 2 to 4 logs more killing than seen with wild-type strains by use of three different phenothiazinium PSs and red light. Mutants that overexpress MDRs were protected from killing compared to the wild type. Effective antimicrobial PSs of different chemical structures showed no difference in light-mediated killing depending on MDR phenotype. Differences in uptake of phenothiazinium PS by the cells depending on level of MDR expression were found. We propose that specific MDR inhibitors could be used in combination with phenothiazinium salts to enhance their photodestructive efficiency.
Simultaneous Detection of Nine Antibiotic Resistance-Related Genes in
Streptococcus agalactiae
Using Multiplex PCR and Reverse Line Blot Hybridization Assay
Authors: Zeng Xianyu , Kong Fanrong , Wang Hui , Darbar Archie , Gilbert Gwendolyn L.
Published: December 2005

Streptococcus agalactiae
(group B streptococcus [GBS]) is the leading cause of neonatal and maternal sepsis. Penicillin is recommended for intrapartum prophylaxis, but erythromycin or clindamycin is used for penicillin-allergic carriers. Antibiotic resistance (AR) has increased recently and needs to be monitored. We have developed a multiplex PCR-based reverse line blot (mPCR/RLB) hybridization assay to detect, simultaneously, seven genes encoding AR—
erm
(A/TR),
erm
(B),
mef
(A/E),
tet
(M),
tet
(O),
aphA-3
, and
aad
-
6
—and two AR-related genes,
int
-Tn and
mreA
. We tested 512 GBS isolates from Asia and Australasia and compared mPCR/RLB with antibiotic susceptibility phenotype or single-gene PCR. Phenotypic resistance to tetracycline was identified in 450 (88%) isolates, of which 442 had
tet
(M) (93%) and/or
tet
(O) (6%). Of 67 (13%) erythromycin-resistant isolates, 18 were susceptible to clindamycin, i.e., had the M phenotype, encoded by
mef
(A/E); 39 had constitutive (cMLS
B
) and 10 inducible clindamycin resistance, and of these, 34 contained
erm
(B) and 12
erm
(A/TR). Of four additional isolates with
mef
(A/E), three contained
erm
(B) with cMLS
B
and one was erythromycin susceptible. Of 61 (12%) clindamycin-resistant isolates, 20 were susceptible to erythromycin and two had intermediate resistance. Based on sequencing, 21 of 22 isolates with
mef
had
mef
(E), and 8 of 353 with
int
-Tn had an atypical sequence. Several AR genes,
erm
(B),
tet
(O),
aphA-3
,
aad
-
6
, and
mef
(A/E), were significantly more common among Asian than Australasian isolates, and there were significant differences in distribution of AR genes between GBS serotypes. Our mPCR/RLB assay is simple, rapid, and suitable for surveillance of antibiotic resistance in GBS.
Effect of Ethanol on Fluoroquinolone Efficacy in a Rat Model of Pneumococcal Pneumonia
Authors: Olsen Keith M. , Gentry-Nielsen Martha , Yue Mei , Snitily Mary U. , Preheim Laurel C.
Published: December 2005

This investigation compared the effect of ethanol on fluoroquinolone antibiotic efficacy and pharmacodynamics in an ethanol-fed rat model of pneumococcal pneumonia. Male Sprague-Dawley rats received a liquid diet containing 36% of total calories as ethanol. Paired controls (pair-fed controls) were fed a liquid diet without ethanol or received rat chow. Diets began 7 days before and continued for 10 days after transtracheal infections with 10 times the 50% lethal dose of type 3
Streptococcus pneumoniae
. Beginning 18 h after infection, the rats received once daily subcutaneous phosphate-buffered saline, levofloxacin, moxifloxacin, or trovafloxacin at 50 or 100 mg/kg of body weight. White blood cell counts were determined, blood samples were collected for culture, and mortality was recorded. Additional rats were killed on day 5 for pharmacodynamic studies and quantitative cultures of bronchoalveolar lavage fluid. Bacteremia occurred by day 3 in 20 of 22 untreated rats. All 22 untreated rats died by day 9. Moxifloxacin treatment was effective in all diet groups at both the 50- and 100-mg/kg doses. In contrast, 50-mg/kg doses of levofloxacin and trovafloxacin improved survival in ethanol-fed rats but were ineffective in chow-fed rats. High-dose trovafloxacin at 100 mg/kg was associated with increased mortality in pair-fed rats. The free-fraction area under the concentration-time curve/MIC ratio exceeded 50 with all antibiotics in the ethanol group but dropped below 30 with levofloxacin and trovafloxacin in the pair- and chow-fed rats, with higher mortality. Achievement of adequate antibiotic-free fraction area under the concentration-time curve/MIC ratios helps overcome ethanol-induced immune defects induced in experimental pneumococcal pneumonia.
Induction and Inhibition of Ciprofloxacin Resistance-Conferring Mutations in Hypermutator Bacteria
Authors: Cirz Ryan T. , Romesberg Floyd E.
Published: December 2005

The emergence of drug-resistant bacteria poses a serious threat to human health. Bacteria often acquire resistance from a mutation of chromosomal genes during therapy. We have recently shown that the evolution of resistance to ciprofloxacin in vivo and in vitro requires the induction of a mutation that is mediated by the cleavage of the SOS repressor LexA and the associated derepression of three specialized DNA polymerases (polymerase II [Pol II], Pol IV, and Pol V). These results led us to suggest that it may be possible to design drugs to inhibit these proteins and that such drugs might be coadministered with antibiotics to prevent mutation and the evolution of resistance. For the approach to be feasible, there must not be any mechanisms through which bacteria can induce mutations and acquire antibiotic resistance that are independent of LexA and its repressed polymerases. Perhaps the most commonly cited mechanism to elevate bacterial mutation rates is the inactivation of methyl-directed mismatch repair (MMR). However, it is unclear whether this represents a LexA-independent mechanism or if the mutations that arise in MMR-deficient hypermutator strains are also dependent on LexA cleavage and polymerase derepression. In this work, we show that LexA cleavage and polymerase derepression are required for the evolution of clinically significant resistance in MMR-defectiveEscherichia coli. Thus, drugs that inhibit the proteins responsible for induced mutations are expected to efficiently prevent the evolution of resistance, even in MMR-deficient hypermutator strains.
First Detection of Metallo-β-Lactamase VIM-2 in
Pseudomonas aeruginosa
Isolates from Colombia
Authors: Villegas Maria Virginia , Lolans Karen , del Rosario Olivera Maria , Suarez Carlos José , Correa Adriana , Queenan Anne Marie , Quinn John P.
Published: December 2005

Carbapenem resistance rates in
Pseudomonas aeruginosa
isolates in Colombia, as in many South American countries, are high for reasons that remain unclear. From our nationwide network, we describe the first detection of the metallo-β-lactamase VIM-2 in clinical isolates of
P. aeruginosa
from multiple cities within Colombia. Metallo-β-lactamases were not detected in the two centers with the highest imipenem resistance rates. Clonality was noted in five of the eight centers with strains meeting the criteria for molecular typing. The high carbapenem resistance in
P. aeruginosa
in Colombia may be attributable to a combination of factors, including the presence of metallo-β-lactamases and nosocomial transmission.
Utility of Muropeptide Ligase for Identification of Inhibitors of the Cell Wall Biosynthesis Enzyme MurF
Authors: Baum Ellen Z. , Crespo-Carbone Steven M. , Abbanat Darren , Foleno Barbara , Maden Amy , Goldschmidt Raul , Bush Karen
Published: December 2005

MurF is a key enzyme in the biosynthesis of the bacterial cell wall in both gram-positive and gram-negative bacteria. This enzyme has not been extensively exploited as a drug target, possibly due to the difficulty in obtaining one of the substrates, UDP-MurNAc-
l
-Ala-γ-
d
-Glu-
meso
-diaminopimelate, which is usually purified from bacteria. We have identified putative inhibitors of
Escherichia coli
MurF by a binding assay, thus bypassing the need for substrate. Inhibition of enzymatic activity was demonstrated in a high-performance liquid chromatography-based secondary assay with UDP-MurNAc-
l
-Ala-γ-
d
-Glu-diaminopimelate substrate prepared in a novel way by using muropeptide ligase enzyme to add UDP-MurNAc to synthetic
l
-Ala-γ-
d
-Glu-diaminopimelate; the substrate specificity of muropeptide ligase for peptides containing
l
-Lys in place of diaminopimelate was also investigated. Using the muropeptide ligase-generated MurF substrate, a thiazolylaminopyrimidine series of MurF enzyme inhibitors with 50% inhibitory concentration values as low as 2.5 μM was identified.
Activity of a New Oral Streptogramin, XRP2868, against Gram-Positive Cocci Harboring Various Mechanisms of Resistance to Streptogramins
Authors: Dupuis Michel , Leclercq Roland
Published: December 2005

The antibacterial activity of XRP2868, a new oral streptogramin composed of a combination of RPR132552 (streptogramin A) and RPR202868 (streptogramin B), was evaluated against a collection of clinical gram-positive isolates with characterized phenotypes and genotypes of streptogramin resistance. The effects of genes for resistance to streptogramin A or B on the activity of XRP2868 and its components were also tested by cloning these genes individually or in various combinations in gram-positive recipient strains susceptible to quinupristin-dalfopristin. The species tested included
Staphylococcus aureus
, coagulase-negative staphylococci,
Enterococcus faecalis
,
Enterococcus faecium
,
Streptococcus pneumoniae
, and other species of streptococci. XRP2868 was generally fourfold more potent than quinupristin-dalfopristin against
S. aureus
,
E. faecium
, and streptococci and had activity against
E. faecalis
(MICs = 0.25 to 1 μg/ml). XRP2868 appeared to be affected by the same mechanisms of resistance as those to quinupristin-dalfopristin. Nevertheless, the strong activity of factor A of the oral streptogramin enabled the combination to be very potent against streptogramin-susceptible staphylococci, streptococci, and
E. faecium
(MICs = 0.03 to 0.25 μg/ml) and to retain low MICs against the strains harboring a mechanism of resistance to factor A or factor B of the streptogramin. However, the combination of mechanisms of resistance to factors A and B caused an increase in the MICs of XRP2868, which reached 1 to 4 μg/ml. As with the other streptogramins, there was a reduction in the bactericidal effect of XRPR2868 when the staphylococcal strains acquired a constitutively expressed
erm
gene.