bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gene Amplification in
Leishmania tarentolae
Selected for Resistance to Sodium Stibogluconate
Authors: Haimeur Anass , Ouellette Marc 
Published: October 2018

ABSTRACT

Leishmania tarentolae
promastigotes were selected step by step for resistance to sodium stibogluconate (Pentostam). Mutants resistant to antimony-containing drugs and cross-resistant to arsenite were therefore obtained. Amplification of one common locus was observed in several independent sodium stibogluconate-resistant mutants, and the locus amplified was novel. The copy number of the amplified locus was related to the level of resistance to pentavalent antimony. The gene responsible for antimony resistance was isolated by transfection and was shown to correspond to an open reading frame coding for 770 amino acids. The putative gene product did not exhibit significant homology with sequences present in data banks, and the putative role of this protein in antimony resistance is discussed.
Antiproliferative Effects and Mechanism of Action of SCH 56592 against
Trypanosoma
(
Schizotrypanum
)
cruzi
: In Vitro and In Vivo Studies
Authors: Urbina Julio A. , Payares Gilberto , Contreras Lellys M. , Liendo Andreína , Sanoja Cristina , Molina Judith , Piras Marta , Piras Romano , Perez Norma , Wincker Patrick , Loebenberg David 
Published: October 2018

ABSTRACT

We have investigated the antiproliferative effects of SCH 56592, a new experimental triazole, against
Trypanosoma
(
Schizotrypanum
)
cruzi
, the etiological agent of Chagas’ disease in Latin America. SCH 56592 blocked the proliferation of the epimastigote form of the parasite in vitro at 30 nM, a concentration 30- to 100-fold lower than that required with the reference compounds ketoconazole and itraconazole. At that concentration all the parasite’s endogenous sterols (ergosterol, 24-ethyl-cholesta-5,7,22-trien-3β-ol, and its 22-dihydro analogs), were replaced by methylated sterols (lanosterol and 24-methylene-dihydrolanosterol), as revealed by high-resolution gas chromatography coupled with mass spectrometry. This indicated that the primary mechanism of action of the drug was inhibition of the parasite’s sterol C-14α demethylase. Against the clinically relevant intracellular amastigote form, grown in cultured Vero cells at 37°C, the MIC of SCH 56592 was 0.3 nM, again 33- to 100-fold lower than that of ketoconazole or itraconazole. In a murine model of acute Chagas’ disease, SCH 56592 given at ≥ 10 mg/kg of body weight/day for a total of 43 doses allowed 85 to 100% survival and 90 to 100% cure of the surviving animals, as verified by parasitological, serological, and PCR-based tests, while ketoconazole given at 30 mg/kg day allowed 60% survival but only 20% cure. In a murine model of chronic Chagas’ disease, SCH 56592 was again more effective than ketoconazole, providing 75 to 85% protection from death, with 60 to 75% parasitological cures of the surviving animals, while no parasitological cures were observed with ketoconazole. The results indicate that SCH 56592 is the most powerful sterol biosynthesis inhibitor ever tested against
T. cruzi
and may be useful in the treatment of human Chagas’ disease.
Population Pharmacokinetics of Ceftizoxime Administered by Continuous Infusion in Clinically Ill Adult Patients
Authors: Facca Bryan , Frame Bill , Triesenberg Steve 
Published: October 2018

ABSTRACT
Ceftizoxime is a widely used beta-lactam antimicrobial agent, but pharmacokinetic data for use with clinically ill patients are lacking. We studied the population pharmacokinetics of ceftizoxime in 72 clinically ill patients at a community-based, university-affiliated hospital. A population pharmacokinetic model for ceftizoxime was created by using a prospective observational design. Ceftizoxime was administered by continuous infusion to treat patients with proven or suspected bacterial infections. While the patients were receiving infusions of ceftizoxime, serum samples were collected for pharmacokinetic analysis with the nonlinear mixed-effect modeling program NONMEM. In addition to clearance and volume of distribution, various comorbidities were examined for their influence on the kinetics. All 72 subjects completed the study, and 114 serum samples were collected. Several demographic and comorbidity variables, namely, age, weight, serum creatinine levels, congestive heart failure, and long-term ventilator dependency, had a significant impact on the estimate for ceftizoxime clearance. A mixture model, or two populations for estimation of ceftizoxime clearance, was discovered. One population presented with an additive clearance component of 1.6 liters per h. In addition, a maximizer function for serum creatinine levels was found. In summary, two models for ceftizoxime clearance, mixture and nonmixture, were found and are presented. Clearance for ceftizoxime can be estimated with commonly available clinical information and the models presented. From the clearance estimates, the dose of ceftizoxime to maintain the desired concentration in serum can be determined. Work is needed to validate the model for drug clearance and to evaluate its predictive performance.
Metabolism of 2′,3′-Dideoxy-2′,3′-Didehydro-β-
l
(−)-5-Fluorocytidine and Its Activity in Combination with Clinically Approved Anti-Human Immunodeficiency Virus β-
d
(+) Nucleoside Analogs In Vitro
Authors: Dutschman Ginger E. , Bridges Edward G. , Liu Shwu-Huey , Gullen Elizabeth , Guo Xin , Kukhanova Marina , Cheng Yung-Chi 
Published: October 2018

ABSTRACT

2′,3′-Dideoxy-2′,3′-didehydro-β-
l
(−)-5-fluorocytidine [
l
(−)Fd4C] has been reported to be a potent inhibitor of the human immunodeficiency virus (HIV) in cell culture. In the present study the antiviral activity of this compound in two-drug combinations and its intracellular metabolism are addressed. The two-drug combination of
l
(−)Fd4C plus 2′,3′-didehydro-2′,3′-dideoxythymidine (D4T, or stavudine) or 3′-azido-3′-deoxythymidine (AZT, or zidovudine) synergistically inhibited replication of HIV in vitro. Additive antiviral activity was observed with
l
(−)Fd4C in combination with 2′,3′-dideoxycytidine (ddC, or zalcitabine) or 2′,3′-dideoxyinosine (ddI, or didanosine). This β-
l
(−) nucleoside analog has no activity against mitochondrial DNA synthesis at concentrations up to 10 μM. As we previously reported for other β-
l
(−) nucleoside analogs,
l
(−)Fd4C could protect against mitochondrial toxicity associated with D4T, ddC, and ddI. Metabolism studies showed that this drug is converted intracellularly to its mono-, di-, and triphosphate metabolites. The enzyme responsible for monophosphate formation was identified as cytoplasmic deoxycytidine kinase, and the

K
m

is 100 μM.
l
(−)Fd4C was not recognized in vitro by human mitochondrial deoxypyrimidine nucleoside kinase. Also,
l
(−)Fd4C was not a substrate for deoxycytidine deaminase.
l
(−)Fd4C 5′-triphosphate served as an alternative substrate to dCTP for incorporation into DNA by HIV reverse transcriptase. The favorable anti-HIV activity and protection from mitochondrial toxicity by
l
(−)Fd4C in two-drug combinations favors the further development of
l
(−)Fd4C as an anti-HIV agent.
Detection of Point Mutations inrpoBGene of Rifampin-ResistantRickettsia typhi
Authors: Troyer Jill Michelle , Radulovic Suzana , Andersson Siv G. E. , Azad Abdu F. 
Published: October 2018

ABSTRACTTherpoBgene of rifampin-resistantRickettsia typhi(Rif mutant) and wild-typeR. typhiwere sequenced and compared. The Rif mutantrpoBhad three nucleotide substitutions, which resulted in amino acid changes at residues 151, 201, and 271 and may be the basis for the rifampin resistance.
Contribution of
rpoB
Mutations to Development of Rifamycin Cross-Resistance in
Mycobacterium tuberculosis
Authors: Williams D. L. , Spring L. , Collins L. , Miller L. P. , Heifets L. B. , Gangadharam P. R. J. , Gillis T. P. 
Published: October 2018

ABSTRACT

The contributions of 23 insertion, deletion, or missense mutations within an 81-bp fragment of
rpoB
, the gene encoding the β-subunit of the DNA-dependent RNA polymerase of
Mycobacterium tuberculosis
, to the development of resistance to rifamycins (rifampin, rifabutin, rifapentine, and KRM-1648) in 29 rifampin-resistant clinical isolates were defined. Specific mutant
rpoB
alleles led to the development of cross-resistance to all rifamycins tested, while a subset of mutations were associated with resistance to rifampin and rifapentine but not to KRM-1648 or rifabutin. To further study the impact of specific
rpoB
mutant alleles on the development of rifamycin resistance, mutations were incorporated into the
rpoB
gene of
M. tuberculosis
H37Rv, contained on a mycobacterial shuttle plasmid, by in vitro mutagenesis. Recombinant
M. tuberculosis
clones containing plasmids with specific mutations in either codon 531 or 526 of
rpoB
exhibited high-level resistance to all rifamycins tested, whereas clones containing a plasmid with a mutation in codon 516 exhibited high-level resistance to rifampin and rifapentine but were susceptible to both rifabutin and KRM-1648. These results provided additional proof of the association of specific
rpoB
mutations with the development of rifamycin resistance and corroborate previous reports of the usefulness of
rpoB
genotyping for predicting rifamycin-resistant phenotypes.
Y-688, a New Quinolone Active against Quinolone-Resistant
Staphylococcus aureus
: Lack of In Vivo Efficacy in Experimental Endocarditis
Authors: Entenza J. M. , Marchetti O. , Glauser M. P. , Moreillon P. 
Published: October 2018

ABSTRACT

Y-688 is a new fluoroquinolone with increased activity against ciprofloxacin-resistant staphylococci. The MICs of Y-688 and other quinolones were determined for 58 isolates of ciprofloxacin-resistant and methicillin-resistant
Staphylococcus aureus
(MRSA). The MICs at which 50% and 90% of bacteria were inhibited were ≥128 and ≥128 mg/liter, respectively, for ciprofloxacin, 16 and 32 mg/liter, respectively, for sparfloxacin, and 0.25 and 1 mg/liter, respectively, for Y-688. This new quinolone was further tested in rats with experimental endocarditis due to either of two isolates of ciprofloxacin-resistant MRSA (namely, P8/128 and CR1). Infected animals were treated for 3 days with ciprofloxacin, vancomycin, or Y-688. Antibiotics were administered through a computerized pump to simulate human-like pharmacokinetics in the serum of rats. The anticipated peak and trough levels of Y-688 were 4 and 1 mg/liter at 0.5 and 12 h, respectively. Treatment with ciprofloxacin was ineffective. Vancomycin significantly decreased vegetation bacterial counts for both organisms (
P
≲ 0.05). In contrast, Y-688 only marginally decreased vegetation bacterial counts (
P
≳ 0.05). Moreover, several vegetation that failed Y-688 treatment grew staphylococci for which the MICs of the test antibiotic were increased two to eight times. Y-688 also selected for resistance in vitro, and isolates for which the MICs were increased eight times emerged at a frequency of ca. 10
−8
. Thus, in spite of its low MIC for ciprofloxacin-resistant MRSA, Y-688 failed in vivo and its use carried the risk of resistance selection. The fact that ciprofloxacin-resistant staphylococci became rapidly resistant to this potent new drug suggests that the treatment of ciprofloxacin-resistant MRSA with new quinolones might be more problematic than expected.
Structure of CARB-4 and AER-1 CarbenicillinHydrolyzing β-Lactamases
Authors: Sanschagrin François , Bejaoui Noureddine , Levesque Roger C. 
Published: October 2018

ABSTRACT

We determined the nucleotide sequences of

bla
CARB-4

encoding CARB-4 and deduced a polypeptide of 288 amino acids. The gene was characterized as a variant of group 2c carbenicillin-hydrolyzing β-lactamases such as PSE-4, PSE-1, and CARB-3. The level of DNA homology between the
bla
genes for these β-lactamases varied from 98.7 to 99.9%, while that between these genes and

bla
CARB-4

encoding CARB-4 was 86.3%. The

bla
CARB-4

gene was acquired from some other source because it has a G+C content of 39.1%, compared to a G+C content of 67% for typical
Pseudomonas aeruginosa
genes. DNA sequencing revealed that

bla
AER-1

shared 60.8% DNA identity with

bla
PSE-3

encoding PSE-3. The deduced AER-1 β-lactamase peptide was compared to class A, B, C, and D enzymes and had 57.6% identity with PSE-3, including an STHK tetrad at the active site. For CARB-4 and AER-1, conserved canonical amino acid boxes typical of class A β-lactamases were identified in a multiple alignment. Analysis of the DNA sequences flanking

bla
CARB-4

and

bla
AER-1

confirmed the importance of gene cassettes acquired via integrons in
bla
gene distribution.
Cloning and Nucleotide Sequences of the Topoisomerase IV
parC
and
parE
Genes of
Mycoplasma hominis
Authors: Bébéar Cécile M. , Charron Alain , Bové Joseph Marie , Bébéar Christiane , Renaudin Joel 
Published: October 2018

ABSTRACT

The topoisomerase IV
parC
and
parE
genes from the wall-less organism
Mycoplasma hominis
PG21 were cloned and sequenced. The coupled genes are located far from the DNA gyrase genes
gyrA
and
gyrB
. They encode proteins of 639 and 866 amino acids, respectively. As expected, the encoded ParE and ParC proteins exhibit higher homologies with the topoisomerase IV subunits of the gram-positive bacteria
Staphylococcus aureus
and
Streptococcus pneumoniae
than with their
Escherichia coli
counterparts. The conserved regions include the Tyr residue of the active site and the region involved in quinolone resistance (quinolone resistance-determining region [QRDR]) in ParC and the ATP-binding site and the QRDR in ParE.
Prevalence of a Putative Efflux Mechanism among Fluoroquinolone-Resistant Clinical Isolates of
Streptococcus pneumoniae
Authors: Brenwald Nigel P. , Gill Martin J. , Wise Richard 
Published: October 2018

ABSTRACT

Twenty-three norfloxacin-selected first-step mutants of
Streptococcus pneumoniae
showed low-level fluoroquinolone resistance. Their susceptibility to norfloxacin in the presence or absence of reserpine and known efflux pump substrates was determined by an agar dilution method. Five mutants showed four- to eightfold increases in their susceptibility to norfloxacin in the presence of reserpine and four- to eightfold decreases in their susceptibility to acriflavine and ethidium bromide. This phenotype is suggestive of an efflux mechanism of resistance. A representative of these mutants, 1N27, accumulated significantly less ethidium bromide than the parent strain; reserpine abolished these differences. No changes in the quinolone resistance-determining regions of
parC
,
parE
,
gyrA
, or
gyrB
were found in this mutant. By our validated agar dilution method, the efflux phenotype was sought in clinical isolates of
S. pneumoniae
. Of 1,037 clinical isolates examined from the United Kingdom, 273 showed reduced susceptibility to norfloxacin or ciprofloxacin. Of these, 45.4% showed the efflux phenotype. Our findings suggest that an efflux mechanism may be a frequent cause of clinically significant fluoroquinolone resistance in pneumococci.
Pharmacokinetics of [
18
F]Trovafloxacin in Healthy Human Subjects Studied with Positron Emission Tomography
Authors: Fischman Alan J. , Babich John W. , Bonab Ali A. , Alpert Nathaniel M. , Vincent John , Callahan Ronald J. , Correia John A. , Rubin Robert H. 
Published: October 2018

ABSTRACT

Tissue pharmacokinetics of trovafloxacin, a new broad-spectrum fluoroquinolone antimicrobial agent, were measured by positron emission tomography (PET) with [
18
F]trovafloxacin in 16 healthy volunteers (12 men and 4 women). Each subject received a single oral dose of trovafloxacin (200 mg) daily beginning 5 to 8 days before the PET measurements. Approximately 2 h after the final oral dose, the subject was positioned in the gantry of the PET camera, and 1 h later 10 to 20 mCi of [
18
F]trovafloxacin was infused intravenously over 1 to 2 min. Serial PET images and blood samples were collected for 6 to 8 h, starting at the initiation of the infusion. Drug concentrations were expressed as the percentage of injected dose per gram, and absolute concentrations were estimated by assuming complete absorption of the final oral dose. In most tissues, there was rapid accumulation of the radiolabeled drug, with high levels achieved within 10 min after tracer infusion. Peak concentrations of more than five times the MIC at which 90% of the isolates are inhibited (MIC
90
) for most members of
Enterobacteriaceae
and anaerobes (>10-fold for most organisms) were achieved in virtually all tissues, and the concentrations remained above this level for more than 6 to 8 h. Particularly high peak concentrations (micrograms per gram; mean ± standard error of the mean [SEM]) were achieved in the liver (35.06 ± 5.89), pancreas (32.36 ± 20.18), kidney (27.20 ± 10.68), lung (22.51 ± 7.11), and spleen (21.77 ± 11.33). Plateau concentrations (measured at 2 to 8 h; micrograms per gram; mean ± SEM) were 3.25 ± 0.43 in the myocardium, 7.23 ± 0.95 in the lung, 11.29 ± 0.75 in the liver, 9.50 ± 2.72 in the pancreas, 4.74 ± 0.54 in the spleen, 1.32 ± 0.09 in the bowel, 4.42 ± 0.32 in the kidney, 1.51 ± 0.15 in the bone, 2.46 ± 0.17 in the muscle, 4.94 ± 1.17 in the prostate, and 3.27 ± 0.49 in the uterus. In the brain, the concentrations (peak, ∼2.63 ± 1.49 μg/g; plateau, ∼0.91 ± 0.15 μg/g) exceeded the MIC
90
s for such common causes of central nervous system infections as
Streptococcus pneumoniae
(MIC
90
, <0.2 μg/ml),
Neisseria meningitidis
(MIC
90
, <0.008 μg/ml), and
Haemophilus influenzae
(MIC
90
, <0.03 μg/ml). These PET results suggest that trovafloxacin will be useful in the treatment of a broad range of infections at diverse anatomic sites.
Topoisomerase Mutations in Trovafloxacin-Resistant
Staphylococcus aureus
Authors: Fitzgibbon Joseph E. , John Joseph F. , Delucia Jennifer L. , Dubin Donald T. 
Published: October 2018

ABSTRACT

A total of 201
Staphylococcus aureus
isolates were surveyed for susceptibility to ciprofloxacin and trovafloxacin. Of 66 methicillin-resistant isolates, 89% were ciprofloxacin resistant and 6% were also trovafloxacin resistant. Trovafloxacin-resistant strains had unusual patterns of quinoline resistance mutations in DNA topoisomerase genes, including two mutations in the A subunit (encoded by
grlA
) of topoisomerase IV.
The M539V Polymerase Variant of Human Hepatitis B Virus Demonstrates Resistance to 2′-Deoxy-3′-Thiacytidine and a Reduced Ability to Synthesize Viral DNA
Authors: Ladner Stephanie K. , Miller Thomas J. , King Robert W. 
Published: October 2018

ABSTRACT
The cytosine analog 2′-deoxy-3′-thiacytidine (3TC) has been shown to be an effective treatment for chronic hepatitis B virus (HBV) infection. However, several liver transplant patients who were undergoing treatment with 3TC for HBV infection experienced a breakthrough of virus while on 3TC. The predominant virus found in these patients’ sera contained either a valine or isoleucine for the methionine in the highly conserved YMDD nucleotide binding site in the HBV polymerase. To determine the biological relevance of the Met-to-Val substitution, we mutated a plasmid that contained a cDNA copy of the HBV pregenomic RNA such that when virus replication occurred during transient transfection of HepG2 cells, an M539V polymerase variant was produced. We found that in transiently transfected cells, this variant was approximately 330-fold less sensitive to the antiviral effects of 3TC and produced 7-fold less viral DNA than the wild type.
Iron-Limited Biofilms of
Candida albicans
and Their Susceptibility to Amphotericin B
Authors: Baillie George S. , Douglas L. Julia 
Published: October 2018

ABSTRACT

Biofilms of
Candida albicans
were grown in vitro under iron limitation and at a low growth rate to simulate conditions for implant-associated biofilms in vivo. Their properties were compared with those of glucose-limited biofilms grown under analogous conditions. At steady state, the adherent cell populations of iron-limited biofilms were double those of glucose-limited biofilms, although the growth rates were similar (0.038 to 0.043 h
−1
). Both biofilm types were resistant to amphotericin B, but daughter cells from iron-limited biofilms were significantly more susceptible to the drug than those from glucose-limited biofilms.
Pharmacokinetics and Distribution over the Blood-Brain Barrier of Zalcitabine (2′,3′-Dideoxycytidine) and BEA005 (2′,3′-Dideoxy-3′-Hydroxymethylcytidine) in Rats, Studied by Microdialysis
Authors: Borg Natalia , Ståhle Lars 
Published: October 2018

ABSTRACT

Microdialysis was applied to sample the unbound drug concentration in the extracellular fluid in brain and muscle of rats given zalcitabine (2′,3′-dideoxycytidine;
n
= 4) or BEA005 (2′,3′-dideoxy-3′-hydroxymethylcytidine;
n
= 4) (50 mg/kg of body weight given subcutaneously). Zalcitabine and BEA005 were analyzed by high-pressure liquid chromatography with UV detection. The maximum concentration of zalcitabine in the dialysate (
C
max
) was 31.4 ± 5.1 μM (mean ± standard error of the mean) for the brain and 238.3 ± 48.1 μM for muscle. The time to
C
max
was found to be from 30 to 45 min for the brain and from 15 to 30 min for muscle. Zalcitabine was eliminated from the brain and muscle with half-lives 1.28 ± 0.64 and 0.85 ± 0.13 h, respectively. The ratio of the area under the concentration-time curve (AUC) (from 0 to 180 min) for the brain and the AUC for muscle (AUC ratio) was 0.191 ± 0.037. The concentrations of BEA005 attained in the brain and muscle were lower than those of zalcitabine, with
C
max
s of 5.7 ± 1.4 μM in the brain and 61.3 ± 12.0 μM in the muscle. The peak concentration in the brain was attained 50 to 70 min after injection, and that in muscle was achieved 30 to 50 min after injection. The half-lives of BEA005 in the brain and muscle were 5.51 ± 1.45 and 0.64 ± 0.06 h, respectively. The AUC ratio (from 0 to 180 min) between brain and muscle was 0.162 ± 0.026. The log octanol/water partition coefficients were found to be −1.19 ± 0.04 and −1.47 ± 0.01 for zalcitabine and BEA005, respectively. The degrees of plasma protein binding of zalcitabine (11% ± 4%) and BEA005 (18% ± 2%) were measured by microdialysis in vitro. The differences between zalcitabine and BEA005 with respect to the AUC ratio (
P
= 0.481), half-life in muscle (
P
= 0.279), and level of protein binding (
P
= 0.174) were not statistically significant. The differences were statistically significant in the case of the half-life in the brain (
P
= 0.032), clearance (
P
= 0.046), volume of distribution (
P
= 0.027) in muscle, and octanol/water partition coefficient (
P
= 0.019).