bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical evidence of long‐range atmospheric transport over southern Africa
Authors: Piketh S. J. , Swap R. J. , Maenhaut W. , Annegarn H. J. , Formenti P.
Published: December 2002

Atmospheric stability and many natural and anthropogenic sources lead to the accumulation of aerosols over southern Africa with potential climatic forcing consequences. A trajectory climatology for southern Africa shows that air circulates over the entire region for several days in an anticyclonic type pattern of flow concentrating aerosols and trace gases below 700 or 500 hPa. A long‐term, time‐resolved, size‐fractionated aerosol monitoring site along the locus of one of the main transport routes was established at Ben Macdhui mountain in the eastern Cape (∼30°S, 28°E). Chemical data collected from initial samples indicated that distinctive episodes of industrial‐related emissions are detected at the site using inorganic fine sulfur as a unique tracer. In addition, two intensive sampling campaigns were undertaken to augment the long‐term data set. Emissions from four sources influencing the aerosol content at Ben Macdhui were identified: aeolian dust or soil from the natural landscape, industry, biomass burning, and sea‐salt emissions from the marine environment. The industrial aerosols were transported mostly in an anticyclonic recirculation pattern from the Highveld and had a distinct chemical signature. Some industrial emissions were transported from the east between the site and the east coast of South Africa.
Surface tension of Rax cloud water and its relation to the concentration of organic material
Authors: Hitzenberger R. , Berner A. , Kasper‐Giebl A. , Löflund M. , Puxbaum H.
Published: December 2002

During an intensive field campaign at a midlevel (1640 m above sea level) mountain in central Europe, cloud water samples were collected using a cloud water sampler and subsequently analyzed for organic and inorganic ions, total carbon (TC), and black carbon (BC). Cloud water surface tension (σ) was measured using the ring method. Generally, the cloud water samples had surface tensions lower than that of pure water. The average value of σ was 95.2% of the σ of water, while the lowest value was 83.3%. A trend of lower σ with higher concentrations of organic material (OC, obtained as TC‐BC) was found at lower OC concentrations than those previously described [Charlson et al., 2001; Facchini et al., 1999a]. The effect of the lower σ on cloud droplet activation was modeled using Köhler theory. For an assumed dry sulphate nucleus with 0.05 μm diameter, the critical supersaturation would be decreased by 7% (average σ) and by 22% for minimum σ.
Comparison of water column [CO2aq] with sedimentary alkenone‐based estimates: A test of the alkenone‐CO2proxy
Authors: Pagani Mark , Freeman Katherine H. , Ohkouchi Nao , Caldeira Ken
Published: December 2002

The stable carbon isotopic compositions of alkenones have been used to interpret the long‐term history of the partial pressure of atmospheric carbon dioxide (pCO2). Although extensive water column and culture studies document the potential utility and limitations of this approach, to date the accuracy ofpCO2values derived from sedimentary alkenones remains untested. For this study we establish Holocene‐aged, alkenone‐based CO2aqestimates ([CO2aq]alk) from 20 sites along a central Pacific Ocean transect and compare them against both observed modern water column CO2aqand estimated preindustrial concentrations at the depth of alkenone production at each site. Although the [CO2aq]alktrack measured water column values, they are conspicuously lower than modern values across the subtropics. This offset likely reflects the contributions of anthropogenic CO2in modern surface waters relative to preindustrial concentrations at the time of alkenone production. When a model‐based estimate of anthropogenic CO2is removed from the modern observed values, a majority (84%) of [CO2aq]alkfalls within 20% of modeled preindustrial values. Consistency between the modeled and alkenone‐based estimates of preindustrial CO2levels points to the relative accuracy of the alkenone‐CO2method across a wide range of ocean and biogeographic regimes, provided that phosphate concentrations, at the depth of haptophyte production, are reasonably constrained. It further suggests that light‐limited growth and/or active carbon uptake, if they occur, have a negligible effect on reconstructed [CO2aq].
Surface and deep ocean circulation in the subpolar North Atlantic during the mid‐Pleistocene revolution
Authors: Wright Amy K. , Flower Benjamin P.
Published: December 2002

We investigated surface and deep ocean variability in the subpolar North Atlantic from 1000 to 500 thousand years ago (ka) based on two Ocean Drilling Program (ODP) sites, Feni drift site 980 (55°29′N, 14°42′W) and Bjorn drift site 984 (61°25′N, 24°04′W). Benthic foraminiferal stable isotope data, planktic foraminiferal faunas, ice‐rafted debris data, and faunally based sea‐surface temperature estimates help test the hypothesis that oceanographic changes in the North Atlantic region were associated with the onset of the 100‐kyr world during the mid‐Pleistocene revolution. Based on percentage of Neogloboquadrina pachyderma (s) records from both sites, surface waters during interglacials and glacials were cooler in the mid‐Pleistocene than during marine isotope stages (MIS) 5 and 6. In particular, interglaciations at Bjorn drift site 984 were significantly cooler. Faunal evidence suggests that the interglacial Arctic front shifted from a position between the two sites to a position northwest of Bjorn drift site 984 after ca. 610 ka. As during the late Pleistocene, we find faunal evidence for lagging surface warmth at most of the glacial initiations during the mid‐Pleistocene. Each initiation is associated with high benthic δ13C values that are maintained into the succeeding glaciation, which we term “lagging NADW production.” These findings indicate that lagging warmth and lagging NADW production are robust features of the regional climate system that persist in the middle to late Pleistocene.
Three‐dimensional soil moisture profile retrieval by assimilation of near‐surface measurements: Simplified Kalman filter covariance forecasting and field application
Authors: Walker Jeffrey P. , Willgoose Garry R. , Kalma Jetse D.
Published: December 2002

The Kalman filter data assimilation technique is applied to a distributed three‐dimensional soil moisture model for retrieval of the soil moisture profile in a 6 ha catchment using near‐surface soil moisture measurements. A simplified Kalman filter covariance forecasting methodology is developed based on forecasting of the state correlations and imposed state variances. This covariance forecasting technique, termed the modified Kalman filter, was then used in a 1 month three‐dimensional field application. Two updating scenarios were tested: (1) updating every 2 to 3 days and (2) a single update. The data used were from the Nerrigundah field site, near Newcastle, Australia. This study demonstrates the feasibility of data assimilation in a quasi three‐dimensional distributed soil moisture model, provided simplified covariance forecasting techniques are used. It also identifies that (1) the soil moisture profile cannot be retrieved from near‐surface soil moisture measurements when the near‐surface and deep soil layers become decoupled, such as during extreme drying events; (2) if simulation of the soil moisture profile is already good, the assimilation can result in a slight degradation, but if the simulation is poor, assimilation can yield a significant improvement; (3) soil moisture profile retrieval results are independent of initial conditions; and (4) the required update frequency is a function of the errors in model physics and forcing data.
On the identification of macroscopic root water uptake parameters from soil water content observations
Authors: Hupet F. , Lambot S. , Javaux M. , Vanclooster M.
Published: December 2002

In this paper, we analyze the identification problem of macroscopic root water uptake parameters from soil water content observations. For this study, the macroscopic root water uptake is considered to be linearly decreasing with depth with A and B parameters conditioning, respectively, the maximum root water uptake at the surface and the decreasing rate with depth. For identification of parameter A and B, two different identification approaches are tested using a detailed soil moisture data set consisting of vertical profiles measured with time domain reflectometry (TDR) and neutron probe on 28 locations within a small maize cropped field during a dry period of 26 days. The first approach is based on a simplified water balance, while the second one uses an integrated soil‐vegetation‐atmosphere transfer (SVAT) model in an inverse mode. Results of the simplified water balance show first that the root water uptake measured within the field is quite variable with CV ranging from 22 to 34% for the root uptake parameters A and B, respectively. Furthermore, positive correlation between A and B suggests that low superficial root water uptake could be compensated by high deep root water uptake. Second, numerical simulations used to test the validity of this simplified approach show that the method is quite robust, at least for a certain range of A parameter values (0.008 < A < 0.013), for B, and for all investigated differently textured soils, except the coarse sand. To investigate the feasibility and the robustness of the second approach, we address the problems of insensitivity, instability, and nonuniqueness by means of numerical simulations. Results show, for soils with different textures, that the soil water content and, to a lesser extent, the time derivative of soil water content are quite insensitive to root water uptake parameters, at least compared to soil hydraulic parameters. Furthermore, instability analysis clearly illustrates that root water uptake parameters are quite and even very instable with respect to small uncertainties on the apparently known parameters (e.g., soil parameters). Finally, results show that if root water uptake plus additional other parameters (e.g., soil parameters) are simultaneously optimized, nonuniqueness of parameter sets must be expected. Therefore a robust identification of root water uptake parameters by means of a full SVAT inversion is unlikely to be achieved during a dry period with soil water content observations at least when some other parameters driving the system, like soil hydraulic properties, are not error free. In this context, further in depth research is needed to investigate if the use of longer periods characterized by both drying and redistribution events may increase the success of a full SVAT inversion. Finally, to extend the results of this study, we recommend applying a similar analysis to other macroscopic conceptual root water uptake models.
Vancomycin Acts Synergistically with Gentamicin against Penicillin-Resistant Pneumococci by Increasing the Intracellular Penetration of Gentamicin
Authors: Cottagnoud P. , Cottagnoud M. , Täuber M. G.
Published: December 2002

Vancomycin and gentamicin act synergistically against penicillin-resistant pneumococci in vitro and in experimental rabbit meningitis. The aim of the present study was to investigate the underlying mechanism of this synergism. The intracellular concentration of gentamicin was measured by using the following experimental setting. Bacterial cultures were incubated with either gentamicin alone or gentamicin plus vancomycin for a short period (15 min). The gentamicin concentration was determined before and after grinding of the cultures by using the COBAS INTEGRA fluorescence polarization system (Roche). The grinding efficacies ranged between 44 and 54%, as determined by viable cell counts. In the combination regimen the intracellular concentration of gentamicin increased to 186% compared to that achieved with gentamicin monotherapy. These data suggest that the synergy observed in vivo and in vitro is based on an increased intracellular penetration of the aminoglycoside, probably due to the effect of vancomycin on the permeability of the cell wall.
Bacteremia Due to
Bacteroides fragilis
Group: Distribution of Species, β-Lactamase Production, and Antimicrobial Susceptibility Patterns
Authors: Aldridge Kenneth E. , Ashcraft Deborah , O'Brien Megan , Sanders Charles V.
Published: December 2002

A retrospective analysis of susceptibility data on 542 blood isolates of the
Bacteroides fragilis
group tested from 1987 to 1999 by the same NCCLS-recommended broth microdilution method throughout is presented. Metronidazole, β-lactam-β-lactamase inhibitor combinations, carbapenems, and trovafloxacin were the most active agents (susceptibility of ≥93%). Among the cephalosporin-cephamycins, the order of activity was cefoxitin > ceftizoxime > cefotetan = cefotaxime = cefmetazole > ceftriaxone. All isolates were resistant to penicillin G, and 22% were resistant to clindamycin. The susceptibility rates to piperacillin-tazobactam, imipenem, and meropenem were affected least among isolates resistant to cefoxitin or clindamycin. Except for piperacillin-tazobactam, imipenem, and meropenem, the
B. fragilis
species was more susceptible than were the non-
B. fragilis
species. These data underscore the importance of susceptibility testing of the
B. fragilis
group and can serve as a guide in the choice of empirical antimicrobial therapy.
In Vitro Activities of Cethromycin (ABT-773), a New Ketolide, against
Streptococcus pneumoniae
Strains That Are Not Susceptible to Penicillin or Macrolides
Authors: Mason Edward O. , Lamberth Linda B. , Wald Ellen R. , Bradley John S. , Barson William J. , Kaplan Sheldon L.
Published: December 2002

Pneumococcal resistance to antimicrobials presents problems to physicians for empirical treatment of acute otitis media (AOM). Three hundred thirty-three isolates of
Streptococcus pneumoniae
selected for nonsusceptibility to penicillin (MIC >0.1 μg/ml) from the middle ear (
n
= 325) or mastoid (
n
= 8) of children seen between 1994 and 2000 at four children's hospitals in the United States were tested by broth microdilution for susceptibility to nine antibiotics. Using NCCLS 2002 breakpoints, resistance to the following drugs was as indicated: amoxicillin, 1%; azithromycin, 71%; cefprozil, 71%; ceftriaxone, 2%; cefdinir, 98%; erythromycin, 70%; levofloxacin, 0%; and trimethoprim-sulfamethoxazole, 93%. Of the penicillin- and erythromycin-nonsusceptible isolates, 97% were inhibited by cethromycin (ABT-773) and 83% were inhibited by telithromycin at a concentration of ≤0.125 μg/ml. Macrolide resistance among penicillin-nonsusceptible pneumococci increased from 44 to 80% in the 6 years of the study from which the isolates were selected; however, the proportion of isolates with M or MLS
B
phenotypes remained constant over the time period (53 and 18%, respectively). Prior treatment with a macrolide or clindamycin alone or in combination with a β-lactam resulted in 94 or 85% of isolates causing infections being macrolide and or clindamycin resistant. No prior individual macrolide (azithromycin, erythromycin, or clarithromycin) resulted in more macrolide resistance or in a more prevalent resistance phenotype. The ketolides appear to be active antimicrobials against penicillin- and macrolide-resistant pneumococci.
Simple In Vitro Assay for Determining the Sensitivity of
Plasmodium vivax
Isolates from Fresh Human Blood to Antimalarials in Areas where
P. vivax
Is Endemic
Authors: Russell Bruce M. , Udomsangpetch Rachanee , Rieckmann Karl H. , Kotecka Barbara M. , Coleman Russell E. , Sattabongkot Jetsumon
Published: December 2002

The aim of this study was to develop a simple, field-practical, and effective in vitro method for determining the sensitivity of fresh erythrocytic
Plasmodium vivax
isolates to a range of antimalarials. The method used is a modification of the standard World Health Organization (WHO) microtest for determination of
P. falciparum
drug sensitivity. The WHO method was modified by removing leukocytes and using a growth medium supplemented with AB
+
serum. We successfully carried out 34 in vitro drug assays on 39
P. vivax
isolates collected from the Mae Sod malaria clinic, Tak Province, Thailand. The mean percentage of parasites maturing to schizonts (six or more merozoites) in control wells was 66.5% ± 5.9% (standard deviation). This level of growth in the control wells enabled rapid microscopic determination (5 min per isolate per drug) of the MICs of chloroquine, dihydroartemisinin, WR238605 (tafenoquine), and sulfadoxine.
P. vivax
was relatively sensitive to chloroquine (MIC = 160 ng/ml, 50% inhibitory concentration [IC
50
] = 49.8 ng/ml) and dihydroartemisinin (MIC = 0.5 ng/ml, IC
50
= 0.47 ng/ml). The poor response of
P. vivax
to both tafenoquine (MIC = 14,000 ng/ml, IC
50
= 9,739 ng/ml) and sulfadoxine (MIC = 500,000 ng/ml, IC
50
= 249,000 ng/ml) was due to the slow action of these drugs and the innate resistance of
P. vivax
to sulfadoxine. The in vitro assay developed in our study should be useful both for assessing the antimalarial sensitivity of
P. vivax
populations and for screening new antimalarials in the absence of long-term
P. vivax
cultures.
In Vitro Activities of 7-Substituted 9-Chloro and 9-Amino-2-Methoxyacridines and Their Bis- and Tetra-Acridine Complexes against
Leishmania infantum
Authors: Di Giorgio Carole , Delmas Florence , Filloux Nathalie , Robin Maxime , Seferian Laetitia , Azas Nadine , Gasquet Monique , Costa Muriel , Timon-David Pierre , Galy Jean-Pierre
Published: December 2002

9-Chloro and 9-amino-2-methoxyacridines bearing different substituents in position 7, as well as their corresponding unsubstituted dimeric and tetrameric complexes, were investigated for in vitro antiproliferative properties against
Leishmania infantum
compared to toxicity towards human monocytes. The results clearly confirmed that several compounds of the 2-methoxyacridine series, together with their corresponding dimeric and tetrameric derivatives, had strong in vitro antiparasitic properties. Antileishmanial activity was shown to depend on the nature of both 7- and 9-substituted groups in monoacridines, while it varied according to the nature of the 9-substituted group and the length of the linker among bis- and tetra-acridines. The effects of acridine derivatives on DNA synthesis raised the hypothesis that DNA metabolism constituted their main target in
Leishmania
promastigotes; however, secondary effects on other biochemical pathways, including protein and lipid metabolism, were observed, suggesting that acridine compounds could be considered multitarget drugs.
Exploring the Structure and Function of the Mycobacterial KatG Protein Using
trans
-Dominant Mutants
Authors: DeVito Joseph A. , Morris Sheldon
Published: December 2002

In order to probe the structure and function of the mycobacterial catalase-peroxidase enzyme (KatG), we employed a genetic approach using dominant-negative analysis of
katG
merodiploids. Transformation of
Mycobacterium bovis
BCG with various
katG
point mutants (expressed from low-copy-number plasmids) resulted in reductions in peroxidase and catalase activities as measured in cell extracts. These reductions in enzymatic activity usually correlated with increased resistance to the antituberculosis drug isoniazid (INH). However, for the N138S
trans
-dominant mutant, the catalase-peroxidase activity was significantly decreased while the sensitivity to INH was retained.
trans
-dominance required
katG
expression from multicopy plasmids and could not be demonstrated with
katG
mutants integrated elsewhere on the wild-type
M. bovis
BCG chromosome. Reversal of the mutant phenotype through plasmid exchange suggested the catalase-peroxidase deficiency occurred at the protein level and that INH resistance was not due to a second site mutation(s). Electrophoretic analysis of KatG proteins from the
trans
-dominant mutants showed a reduction in KatG dimers compared to WT and formation of heterodimers with reduced activity. The mutants responsible for these defects cluster around proposed active site residues: N138S, T275P, S315T, and D381G. In an attempt to identify mutants that might delimit the region(s) of KatG involved in subunit interactions, C-terminal truncations were constructed (with and without the D381G dominant-negative mutation). None of the C-terminal deletions were able to complement a Δ
katG
strain, nor could they cause a dominant-negative effect on the WT. Taken together, these results suggest an intricate association between the amino- and carboxy-terminal regions of KatG and may be consistent with a domain-swapping mechanism for KatG dimer formation.
Activity and Diffusion of Tigecycline (GAR-936) in Experimental Enterococcal Endocarditis
Authors: Lefort Agnès , Lafaurie Matthieu , Massias Laurent , Petegnief Yolande , Saleh-Mghir Azzam , Muller-Serieys Claudette , Le Guludec Dominique , Fantin Bruno
Published: December 2002

The activity of tigecycline (GAR-936), a novel glycylcycline, was investigated in vitro and in experimental endocarditis due to the susceptible
Enterococcus faecalis
JH2-2 strain, its VanA type transconjugant BM4316, and a clinical VanA type strain,
E. faecium
HB217 resistant to tetracycline. MICs of GAR-936 were 0.06 μg/ml for the three strains. In vitro pharmacodynamic studies demonstrated a bacteriostatic effect of GAR-936 that was not enhanced by increasing concentrations to more than 1 μg/ml and a postantibiotic effect ranging from 1 to 4.5 h for concentrations of 1- to 20-fold the MIC. Intravenous injection of [
14
C]GAR-936 to five rabbits with enterococcal endocarditis sacrificed 30 min, 4 h, or 12 h after the end of the infusion evidenced a lower clearance of GAR-936 from aortic vegetations than from serum and a homogeneous diffusion of GAR-936 into the vegetations. In rabbits with endocarditis, GAR-936 (14 mg/kg of body weight twice a day [b.i.d.]) given intravenously for 5 days was bacteriostatic against both strains of
E. faecalis
. Against
E. faecium
HB217, bacterial counts in vegetations significantly decreased during therapy (
P
< 0.01), and the effect was similar with GAR-936 at 14 mg/kg b.i.d., 14 mg/kg once a day (o.d.), and 7 mg/kg o.d., which provided concentrations in serum constantly above the MIC. Mean serum elimination half-life ranged from 3.3 to 3.6 h. No GAR-936-resistant mutants were selected in vivo with any regimen. We concluded that the combination of prolonged half-life, significant postantibiotic effect, and good and homogeneous diffusion into the vegetations may account for the in vivo activity of GAR-936 against enterococci susceptible or resistant to glycopeptides and tetracyclines, even when using a o.d. regimen in rabbits.
Chemotherapy with Benznidazole and Itraconazole for Mice Infected with Different
Trypanosoma cruzi
Clonal Genotypes
Authors: Toledo Max Jean de Ornelas , Bahia Maria Terezinha , Carneiro Cláudia M. , Martins-Filho Olindo Assis , Tibayrenc Michel , Barnabé Christian , Tafuri Washington Luis , de Lana Marta
Published: December 2002

The benznidazole (BZ) and itraconazole (ITC) susceptibilities of a standard set of
Trypanosoma cruzi
natural stocks were evaluated during the acute phase and the chronic phase of experimental chagasic infection in BALB/c mice. Twenty laboratory-cloned stocks representative of the total phylogenetic diversity of
T. cruzi
, including genotypes 20 and 19 (
T. cruzi
I) and genotypes 39 and 32 (
T. cruzi
II), were analyzed. Our results demonstrate important differences among stocks that could be pointed out as markers of biological behavior. Members of the
T. cruzi
I group were highly resistant to both BZ and ITC, whereas members of the
T. cruzi
II group were partially resistant to both drugs, despite their susceptibilities to ITC during the chronic phase of infection. The resistance to BZ observed for
T. cruzi
I was mainly triggered by genotype 20 isolates, whereas resistance to ITC was due to both genotype 20 and 19 isolates. Two polar patterns of response to BZ observed for genotype 39 isolates had a major impact on the partial resistance pattern observed for members of the
T. cruzi
II group. Genotype 32 isolates showed a typical profile of susceptibility. The correlation between the response to treatment and phylogenetic classification of
T. cruzi
stocks was clearer for ITC than for BZ. In conclusion, the data presented show a correlation between phylogenetic divergence among
T. cruzi
stocks and their susceptibilities to chemotherapeutic agents in vivo. Our results warn of the necessity to take into account the lesser genetic subdivisions of
T. cruzi
stocks since the upper subdivisions (
T. cruzi
I and II) show a great deal of heterogeneity for in vivo drug susceptibility.
Enzymatic Assay for Measurement of Intracellular DXG Triphosphate Concentrations in Peripheral Blood Mononuclear Cells from Human Immunodeficiency Virus Type 1-Infected Patients
Authors: Kewn Stephen , Wang Laurene H. , Hoggard Patrick G. , Rousseau Franck , Hart Robert , MacNeela John P. , Khoo Saye H. , Back David J.
Published: December 2002

DXG {[2
R
-
cis
]-2-amino-1,9-dihydro-9-[2-[hydroxymethyl]-1,3-dioxolan-4-yl]-6H-purin-6-one} and its prodrug DAPD ([2
R
-
cis
]-4-[2,6-diamino-9H-purin-9-yl]-1,3-dioxolane-2-methanol; amdoxovir) are novel 2′,3′-dideoxynucleosides (ddNs) displaying activity against human immunodeficiency virus type 1 (HIV-1). In this paper, we describe the development of an enzymatic assay for determining the intracellular active metabolite of DXG and DAPD, DXG triphosphate (DXGTP), in peripheral blood mononuclear cells (PBMCs) from HIV-infected patients. The assay involves inhibition of HIV reverse transcriptase (RT), which normally incorporates radiolabeled deoxynucleoside triphosphates (dNTPs) into a synthetic template primer. DXGTP (0.6 pmol) inhibited control product formation with or without a preincubation step. Inhibition was greatest when the template primer was most diluted. DAPDTP inhibited control product formation only at very high levels (50 pmol) and when a preincubation procedure was used. However, reduced template primer stability in assays using preincubation steps, coupled with potential interference by DAPDTP, led to the current assay method for DXGTP being performed without preincubation. Standard DXGTP inhibition curves were constructed. The presence of PBMC extracts or endogenous dGTP did not interfere with the DXGTP assay. Intracellular DXGTP and dGTP concentrations were determined in PBMCs from HIV-infected patients receiving oral DAPD (500 mg b.i.d.). Peak concentrations of DXGTP were obtained 8 h after dosing and were measurable through 48 h postdose. Levels of endogenous dGTP were also determined over 48 h. No direct relationship was observed between concentrations of DXGTP and dGTP. Quantification of DXGTP concentrations in PBMCs from patients receiving a clinically relevant dose of DAPD is possible with this enzymatic assay.
Contributions of MexAB-OprM and an EmrE Homolog to Intrinsic Resistance of
Pseudomonas aeruginosa
to Aminoglycosides and Dyes
Authors: Li Xian-Zhi , Poole Keith , Nikaido Hiroshi
Published: December 2002

Of the six putative small multidrug resistance (SMR) family proteins of
Pseudomonas aeruginosa
, a protein encoded by the PA4990 gene (
emrE
Pae
) shows the highest identity to the well-characterized EmrE efflux transporter of
Escherichia coli
. Reverse transcription-PCR confirmed the expression of
emrE
Pae
in the wild-type strain of
P. aeruginosa
. Using isogenic
emrE
Pae
,
mexAB-oprM
, and/or
mexB
deletion mutants, the contributions of the EmrE protein and the MexAB-OprM efflux system to drug resistance in
P. aeruginosa
were assessed by a drug susceptibility test carried out in a low-ionic-strength medium, Difco nutrient broth. We found that EmrE
Pae
contributed to intrinsic resistance not only to ethidium bromide and acriflavine but also to aminoglycosides. In this low-ionic-strength medium, MexAB-OprM was also shown to contribute to aminoglycoside resistance, presumably via active efflux. Aminoglycoside resistance caused by these two pumps could not be demonstrated in high-ionic-strength media, such as Luria broth or Mueller-Hinton broth. The EmrE-dependent efflux of ethidium bromide was confirmed by a continuous fluorescence assay.
Reactivity of Reduced [2Fe-2S] Ferredoxins Parallels Host Susceptibility to Nitroimidazoles
Authors: Vidakovic Momcilo , Crossnoe Chetlen R. , Neidre Christopher , Kim Kyonghee , Krause Kurt L. , Germanas Juris P.
Published: December 2002

The kinetics of the electron transfer reaction between reduced [2Fe-2S] ferredoxins and select nitroimidazole antimicrobial agents is reported. The ferredoxins from the protozoan
Trichomonas vaginalis
and the cyanobacterium
Anabaena
sp. strain 7120 were studied because they are the proximal electron donors to nitroimidazoles in these two organisms with significantly different nitroimidazole susceptibilities. The rates of electron transfer from
Anabaena
ferredoxin to all nitroimidazoles were 1 to 2 orders of magnitude lower than for
T. vaginalis
ferredoxin. Quantitative structure-activity analysis of the kinetic data showed that the size of the alkyl substituent on the N-1 position of the imidazole ring strongly influenced the magnitude of the electron transfer rate constant. This implies that the distance between the iron-sulfur cluster and the nitro group of the imidazole is the critical variable in determining the rate of electron transfer. A correlation between the magnitude of the one-electron transfer rate constant with the susceptibility of the host organism to the cytotoxic effects of nitroimidazoles was also discovered. These results demonstrate that reductive activation is the most crucial step in determining the toxicity of nitroimidazoles.
Pharmacokinetic-Pharmacodynamic Analysis of Lopinavir-Ritonavir in Combination with Efavirenz and Two Nucleoside Reverse Transcriptase Inhibitors in Extensively Pretreated Human Immunodeficiency Virus-Infected Patients
Authors: Hsu Ann , Isaacson Jeffrey , Brun Scott , Bernstein Barry , Lam Wayne , Bertz Richard , Foit Cheryl , Rynkiewicz Karen , Richards Bruce , King Martin , Rode Richard , Kempf Dale J. , Granneman G. Richard , Sun Eugene
Published: December 2002

The steady-state pharmacokinetics and pharmacodynamics of two oral doses of lopinavir-ritonavir (lopinavir/r; 400/100 and 533/133 mg) twice daily (BID) when dosed in combination with efavirenz, plus two nucleoside reverse transcriptase inhibitors, were assessed in a phase II, open-label, randomized, parallel arm study in 57 multiple protease inhibitor-experienced but non-nucleoside reverse transcriptase inhibitor-naive human immunodeficiency virus (HIV)-infected subjects. All subjects began dosing of lopinavir/r at 400/100 mg BID; subjects in one arm increased the lopinavir/r dose to 533/133 mg BID on day 14. When codosed with efavirenz, the lopinavir/r 400/100 mg BID regimen resulted in lower lopinavir concentrations in plasma, particularlyCmin, than were observed in previous studies of lopinavir/r administered without efavirenz. Increasing the lopinavir/r dose to 533/133 mg increased the lopinavir area under the concentration-time curve over a 12-h dosing interval (AUC12),Cpredose, andCminby 46, 70, and 141%, respectively. The increase in lopinavirCmax(33%,) did not reach statistical significance. Ritonavir AUC12,Cmax,Cpredose, andCminvalues were increased 46 to 63%. The lopinavir predose concentrations achieved with the 533/133-mg BID dose were similar to those observed with lopinavir/r 400/100 mg BID in the absence of efavirenz. Results from univariate logistic regression analyses identified lopinavir and efavirenz inhibitory quotient (IQ) parameters, as well as the baseline lopinavir phenotypic susceptibility, as predictors of antiviral response (HIV RNA < 400 copies/ml at week 24); however, no lopinavir or efavirenz concentration parameter was identified as a predictor. Multiple stepwise logistic regressions confirmed the significance of the IQ parameters, as well as other baseline characteristics, in predicting virologic response at 24 weeks in this patient population.
Drug Targeting
Mycobacterium tuberculosis
Cell Wall Synthesis: Development of a Microtiter Plate-Based Screen for UDP-Galactopyranose Mutase and Identification of an Inhibitor from a Uridine-Based Library
Authors: Scherman Michael S. , Winans Katharine A. , Stern Richard J. , Jones Victoria , Bertozzi Carolyn R. , McNeil Michael R.
Published: December 2002

A microtiter plate assay for UDP-galactopyranose mutase, an essential cell wall biosynthetic enzyme of
Mycobacterium tuberculosis
, was developed. The assay is based on the release of tritiated formaldehyde from UDP-galactofuranose but not UDP-galactopyranose by periodate and was used to identify a uridine-based enzyme inhibitor from a chemical library.
Site-Specific Mutagenesis Analysis of PBP 1A from a Penicillin-Cephalosporin-Resistant Pneumococcal Isolate
Authors: Smith Anthony M. , Klugman Keith P.
Published: December 2002

Our mutagenesis study has investigated all amino acid mutations in the penicillin-binding domain of PBP 1A from Hungarian pneumococcal isolate 3191 to determine the importance of every mutation in the development of penicillin and cefotaxime resistance. Our data reveal that mutations at amino acid positions 574 to 577 and position 539 cause penicillin and cefotaxime resistance.
In Vitro Activities of ABT-773 and Other Antimicrobials against Human Mycoplasmas
Authors: Waites Ken B. , Crabb Donna M. , Duffy Lynn B.
Published: December 2002

The in vitro susceptibilities of 103
Mycoplasma pneumoniae
isolates, 14
Mycoplasma hominis
isolates, 12
Mycoplasma fermentans
isolates, and 24
Ureaplasma
species to ABT-773, an investigational ketolide, and seven other agents were determined. For
M. pneumoniae,
the ABT-773 MIC at which 90% of isolates are inhibited (MIC
90
; ≤0.001 μg/ml) was comparable to those of azithromycin, clarithromycin, and erythromycin and at least 128-fold lower than those of levofloxacin, gatifloxacin, moxifloxacin, and doxycycline. For
M. fermentans
, the ABT-773 MIC
90
(≤0.008 μg/ml) was 2- to 128-fold lower than those of all other agents tested. For
M. hominis
, the ABT-773 MIC
90
(0.031 μg/ml) was equivalent to that of moxifloxacin, 2-fold lower than those of gatifloxacin and clindamycin, and 16-fold lower than that of levofloxacin. ABT-773 was equally active against doxycycline-susceptible and doxycycline-resistant organisms. The ABT-773 MICs (0.016 μg/ml) for
Ureaplasma
species were the lowest of those of any drug tested. The MIC
90
was 4- to 64-fold lower than those of clarithromycin, azithromycin, and erythromycin and ≥16-fold lower than those of all three fluoroquinolones. Minimal bactericidal concentrations determined for a subgroup of organisms were ≤0.063 μg/ml for
M. pneumoniae
and 0.25 μg/ml for
M. fermentans
, but they were several dilutions higher for
M. hominis
and
Ureaplasma
spp. ABT-773 has great potential for further study for the treatment of infections due to mycoplasmas and ureaplasmas.
Escherichia coli
with a Self-Transferable, Multiresistant Plasmid Coding for Metallo-β-Lactamase VIM-1
Authors: Miriagou Vivi , Tzelepi Eva , Gianneli Dimitra , Tzouvelekis Leonidas S.
Published: December 2002

An
Escherichia coli
strain exhibiting decreased susceptibility to carbapenems was isolated from a hospitalized patient in Greece. The strain carried a self-transferable plasmid coding for metallo-β-lactamase VIM-1.
bla
VIM-1
, along with
aacA7
,
dhfrI
, and
aadA
, was included as a gene cassette in a novel class 1 integron. A
Citrobacter freundii ampC
-derived gene, not associated with the integron, was also located in the same plasmid.
Antibiotic Susceptibilities of
Anaplasma
(
Ehrlichia
)
phagocytophilum
Strains from Various Geographic Areas in the United States
Authors: Maurin Max , Bakken Johan S. , Dumler J. Stephen
Published: December 2002

We tested the antibiotic susceptibilities of eight strains of
Anaplasma phagocytophilum
(the agent of human granulocytic ehrlichiosis) collected in various geographic areas of the United States, including Minnesota, Wisconsin, California, and New York. The results are homogeneous and show that doxycycline, rifampin, and levofloxacin are the most active antibiotics against these strains in vitro.
Class 1 Integron-Borne Gene Cassettes in Multidrug-Resistant
Yersinia enterocolitica
Strains of Different Phenotypic and Genetic Types
Authors: Soto S. M. , Lobato M. J. , Mendoza M. C.
Published: December 2002

Seventy nine strains of
Yersinia enterocolitica
resistant to one or more antimicrobials were analyzed for integrons. Only class 1
sul1
integrons containing
aadA1a
(28 strains),
aadA1a-dfr1-sat1
(2 strains), and
dfr1-aadA1a
(1 strain) gene cassettes were found. The first two types were found in clinical isolates belonging to serotype O:3, biotypes 2 to 4, and eight combined ribotypes, and the third was found in the reference strain, CECT4054 (O:8). All screened resistance markers were found in strains with and without integrons (except for chloramphenicol resistance, encoded by
catA1
gene, which was only present in strains with integrons), but in different resistance profiles (R profiles). A profile (ampicillin, streptomycin, sulfadiazine, and trimethoprim resistance, encoded by the
tem1
,
aadA1a
,
sul1
, and
dfr1
genes, respectively) was found in strains, with and without integrons. Integrons and some of the resistance genes are located on plasmids with sizes ranging between 65 and 140 kb. This is the first report of class 1 integrons in
Y. enterocolitica.
In Vivo Antibacterial Activity of RWJ-54428, a New Cephalosporin with Activity against Gram-Positive Bacteria
Authors: Griffith David C. , Harford Laurie , Williams Robert , Lee Ving J. , Dudley Michael N.
Published: December 2002

RWJ-54428 (MC-02,479) is a new cephalosporin with activity against resistant gram-positive organisms, including methicillin-resistant
Staphylococcus aureus
, vancomycin-resistant enterococci, and penicillin-resistant
Streptococcus pneumoniae
. The in vivo efficacy of RWJ-54428 was evaluated against gram-positive bacteria in four mouse models of infection. RWJ-54428 was effective in vivo against methicillin-susceptible and -resistant
S. aureus
in a mouse model of sepsis, with 50% effective doses being similar to those of vancomycin. In a single-dose neutropenic mouse thigh model of infection, RWJ-54428 at 30 mg/kg of body weight showed activity similar to that of vancomycin at 30 mg/kg against a strain of methicillin-resistant
S. aureus
. RWJ-54428 also showed a prolonged in vivo postantibiotic effect in this model. In a mouse model of pneumonia due to a penicillin-susceptible strain of
Streptococcus pneumoniae
, RWJ-54428 displayed efficacy and potency superior to those of penicillin G and cefotaxime. In a mouse model of pyelonephritis due to
Enterococcus faecalis
, RWJ-54428 had bactericidal effects similar to those of vancomycin and ampicillin, but at two- to threefold lower total daily doses. These studies show that RWJ-54428 is active in experimental mouse models of infection against gram-positive organisms, including strains resistant to earlier cephalosporins and penicillin G.
Lincomycin Resistance Mutations in Two Regions Immediately Downstream of the −10 Region of
lmr
Promoter Cause Overexpression of a Putative Multidrug Efflux Pump in
Bacillus subtilis
Mutants
Authors: Kumano Miyuki , Fujita Masaya , Nakamura Kouji , Murata Makiko , Ohki Reiko , Yamane Kunio
Published: December 2002

We isolated 19 lincomycin-resistant
Bacillus subtilis
mutants by expressing
lmrB
encoding a putative multidrug efflux protein. Eighteen of the mutants altered at two regions (−3 to −1 and +15) immediately downstream of the −10 region of the
lmr
promoter increased
lmr
transcription in vivo and in vitro.
Fourteen-Member Macrolides Promote the Phosphatidylserine Receptor-Dependent Phagocytosis of Apoptotic Neutrophils by Alveolar Macrophages
Authors: Yamaryo Takeshi , Oishi Kazunori , Yoshimine Hiroyuki , Tsuchihashi Yoshiko , Matsushima Kouji , Nagatake Tsuyoshi
Published: December 2002

An inflammation of the airway of patients with diffuse panbronchiolitis (DPB), is characterized by dense neutrophil infiltration. Resolution of the inflammation can be achieved by the removal of apoptotic neutrophils by human alveolar macrophages (AM) without liberating neutrophil proteases in the airway. To understand clinical efficacy for the treatment of DPB by 14- or 15-member macrolides, their effects on the phagocytosis of apoptotic neutrophils by AM were examined. Treatment of AM with erythromycin (ERY) or clarithromycin at clinically achievable levels significantly increased the levels of phagocytosis of apoptotic neutrophils. A serum factor was not essential for the enhancement by these 14-member macrolides. Of the antibiotics tested, these effects were specific for the 14-member macrolides and a 15-member macrolide, azithromycin, but not for the 16-member macrolides, clindamycin or β-lactam antibiotics. The enhanced phagocytosis of apoptotic neutrophils by ERY had no effect on the levels of interleukin-8 or tumor necrosis factor alpha production by lipopolysaccharide-stimulated AM after phagocytosis of the apoptotic neutrophils. The increased phagocytosis of apoptotic neutrophils by ERY was also found to be phosphatidylserine receptor-dependent for AM. These data indicate a novel anti-inflammatory action of 14-member and 15-member macrolides, and suggest that such antibiotics achieve clinical efficacy for patients with DPB, in part, through enhancing the nonphlogistic phagocytosis of apoptotic neutrophils by AM.
Mannopeptimycins, New Cyclic Glycopeptide Antibiotics Produced by
Streptomyces hygroscopicus
LL-AC98: Antibacterial and Mechanistic Activities
Authors: Singh M. P. , Petersen P. J. , Weiss W. J. , Janso J. E. , Luckman S. W. , Lenoy E. B. , Bradford P. A. , Testa R. T. , Greenstein M.
Published: December 2002

Mannopeptimycins α, β, γ, δ, and ε are new cyclic glycopeptide antibiotics produced by
Streptomyces hygroscopicus
LL-AC98. Mannopeptimycins γ, δ, and ε, which have an isovaleryl substitution at various positions on the terminal mannose of the disaccharide moiety, demonstrated moderate to good antibacterial activities. Mannopeptimycin ε was the most active component against methicillin-resistant staphylococci and vancomycin-resistant enterococci (MICs, 2 to 4 μg/ml for staphylococci and streptococci and 4 to 32 μg/ml for enterococci), while mannopeptimycins γ and δ were two- to fourfold less active. Mannopeptimycins α and β, which lack the isovaleryl substitution and the disaccharide moiety, respectively, had poor antibacterial activities. The in vivo efficacies of the mannopeptimycins in
Staphylococcus aureus
mouse protection studies paralleled their in vitro activities. The median effective doses of mannopeptimycins γ, δ, and ε were 3.8, 2.6, and 0.59 mg/kg of body weight, respectively. The mannopeptimycins were inactive against cell wall-deficient
S. aureus
and caused spheroplasting of
Escherichia coli imp
similar to that observed with penicillin G in an osmotically protective medium. Mannopeptimycin δ rapidly inhibited [
3
H]
N
-acetylglucosamine incorporation into peptidoglycan in
Bacillus subtilis
and had no effect on DNA, RNA, or protein biosynthesis. On the basis of the observations presented above, an effect on cell wall biosynthesis was suggested as the primary mode of action for mannopeptimycin δ. The mannopeptimycins were inactive against
Candida albicans
, did not initiate hemolysis of human erythrocytes, and did not promote potassium ion leakage from
E. coli imp
, suggesting a lack of membrane damage to prokaryotic or eukaryotic cells.
VanD-Type Vancomycin-ResistantEnterococcus faecium10/96A
Authors: Depardieu Florence , Reynolds Peter E. , Courvalin Patrice
Published: December 2002

VanD typeEnterococcus faecium10/96A is constitutively resistant to vancomycin and to low levels of teicoplanin by nearly exclusive synthesis of peptidoglycan precursors terminating ind-alanyl-d-lactate (L. M. Dalla Costa, P. E. Reynolds, H. A. Souza, D. C. Souza, M. F. Palepou, and N. Woodford, Antimicrob. Agents Chemother. 44:3444-3446, 2000). A G184S mutation adjacent to the serine involved in the binding ofd-Ala1 in thed-alanine:d-alanine ligase (Ddl) led to production of an impaired Ddl and accounts for the lack ofd-alanyl-d-alanine-containing peptidoglycan precursors. The sequence of thevanDgene cluster revealed eight open reading frames. The organization of this operon, assigned to a chromosomal location, was similar to those in other VanD type strains. The distal part encoded the VanHDdehydrogenase, the VanD ligase, and the VanXDdipeptidase, which were homologous to the corresponding proteins in VanD-type strains. Upstream from the structural genes for these proteins was thevanYDgene; a frameshift mutation in this gene resulted in premature termination of the encoded protein and accounted for the lack of penicillin-susceptibled,d-carboxypeptidase activity. Analysis of the translated sequence downstream from the stop codon, but in a different reading frame because of the frameshift mutation, indicated homology with penicillin binding proteins (PBPs) with a high degree of identity with VanYDfrom VanD-type strains. The 5′ end of the gene cluster contained thevanRD-vanSDgenes for a putative two-component regulatory system. Insertion of ISEfa4in thevanSDgene led to constitutive expression of vancomycin resistance. This new insertion belonged to the IS605family and was composed of two open reading frames encoding putative transposases of two unrelated insertion sequence elements, IS200and IS1341.
Contribution of the 8-Methoxy Group to the Activity of Gatifloxacin against Type II Topoisomerases of
Streptococcus pneumoniae
Authors: Kishii Ryuta , Takei Masaya , Fukuda Hideyuki , Hayashi Katsuhiko , Hosaka Masaki
Published: December 2002

The inhibitory activities (50% inhibitory concentrations [IC
50
s]) of gatifloxacin and other quinolones against both DNA gyrase and topoisomerase IV of the wild-type
Streptococcus pneumoniae
IID553 were determined. The IC
50
s of 10 compounds ranged from 4.28 to 582 μg/ml against DNA gyrase and from 1.90 to 35.2 μg/ml against topoisomerase IV. The inhibitory activity against DNA gyrase was more varied than that against topoisomerase IV among fluoroquinolones. The IC
50
s for DNA gyrase of the 8-methoxy quinolones gatifloxacin and AM-1147 were approximately seven times lower than those of their 8-H counterparts AM-1121 and ciprofloxacin, whereas the IC
50
s for topoisomerase IV were 1.5 times lower. Moreover, the IC
50
ratios (IC
50
for DNA gyrase/IC
50
for topoisomerase IV) of gatifloxacin, AM-1147, and moxifloxacin, which possess 8-methoxy groups, were almost the same. The 8-methoxy quinolones showed higher antibacterial activity and less mutant selectivity against IID553 than their 8-H counterparts. These results suggest that the 8-methoxy group enhances both target inhibition, especially for DNA gyrase, leading to potent antipneumococcal activity and dual inhibition against both DNA gyrase and topoisomerase IV in the bacterial cell.