bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combination of Candidate Microbicides Cellulose Acetate 1,2-Benzenedicarboxylate and UC781 Has Synergistic and Complementary Effects against Human Immunodeficiency Virus Type 1 Infection
Authors: Liu Shuwen , Lu Hong , Neurath A. Robert , Jiang Shibo 
Published: April 2005

ABSTRACT

The combination of two candidate microbicides, cellulose acetate 1,2-benzenedicarboxylate (CAP), a polymer that blocks human immunodeficiency virus type 1 (HIV-1) entry by targeting gp120 and gp41, and UC781, a tight-binding HIV-1 reverse transcriptase inhibitor (RTI), resulted in effective synergy for inhibition of MT-2 cell infection by HIV-1
IIIB
, a laboratory-adapted virus strain. The 95% effective concentration values for the combination were reduced about 15- to 20-fold compared with those corresponding to the single compounds. The combination of CAP and UC781 is also synergistic in inhibiting infection of peripheral blood mononuclear cells by a primary HIV-1 isolate, 92US657. Combinations of CAP with other RTIs, such as efavirenz or zidovudine, also had significant synergistic effects on the inhibition of HIV-1 infection. In addition, CAP and UC781 had complementary effects against HIV-1 infection since (i) CAP inhibited infection by the UC781-resistant strain HIV-1
IIIB
A17 and (ii) pretreatment of MT-2 cells with UC781, but not CAP, abolished subsequent infection after removal of the compound. This suggests that the combination of CAP and UC781 represents a promising candidate microbicide for prevention of sexual transmission of HIV-1.
A Novel MATE Family Efflux Pump Contributes to the Reduced Susceptibility of Laboratory-Derived
Staphylococcus aureus
Mutants to Tigecycline
Authors: McAleese Fionnuala , Petersen Peter , Ruzin Alexey , Dunman Paul M. , Murphy Ellen , Projan Steven J. , Bradford Patricia A. 
Published: April 2005

ABSTRACT

Tigecycline, an expanded-broad-spectrum glycylcycline antibiotic is not affected by the classical tetracycline resistance determinants found in
Staphylococcus aureus
. The in vitro selection of mutants with reduced susceptibility to tigecycline was evaluated for two methicillin-resistant
S. aureus
strains by serial passage in increasing concentrations of tigecycline. Both strains showed a stepwise elevation in tigecycline MIC over a period of 16 days, resulting in an increase in tigecycline MIC of 16- and 32-fold for N315 and Mu3, respectively. Transcriptional profiling revealed that both mutants exhibited over 100-fold increased expression of a gene cluster,
mepRAB
(multidrug export protein), encoding a MarR-like transcriptional regulator (
mepR
), a novel MATE family efflux pump (
mepA
), and a hypothetical protein of unknown function (
mepB
). Sequencing of the
mepR
gene in the mutant strains identified changes that presumably inactivated the MepR protein, which suggested that MepR functions as a repressor of
mepA
. Overexpression of
mepA
in a wild-type background caused a decrease in susceptibility to tigecycline and other substrates for MATE-type efflux pumps, although it was not sufficient to confer high-level resistance to tigecycline. Complementation of the
mepR
defect by overexpressing a wild-type
mepR
gene reduced
mepA
transcription and lowered the tigecycline MIC in the mutants. Transcription of
tet
(M) also increased by over 40-fold in the Mu3 mutant. This was attributed to a deletion in the promoter region of the gene that removed a stem-loop responsible for transcriptional attenuation. However, overexpression of the
tet
(M) transcript in a tigecycline-susceptible strain was not enough to significantly increase the MIC of tigecycline. These results suggest that the overexpression of
mepA
but not
tet
(M) may contribute to decreased susceptibility of tigecycline in
S. aureus
.
Evolution of TEM-Type Extended-Spectrum β-Lactamases in Clinical
Enterobacteriaceae
Strains in Poland
Authors: Baraniak Anna , Fiett Janusz , Mrówka Agnieszka , Walory Jarosław , Hryniewicz Waleria , Gniadkowski Marek 
Published: April 2005

ABSTRACT

Seventeen extended-spectrum β-lactamase (ESBL)-producing isolates of the family
Enterobacteriaceae
recovered from 1998 to 2000 in hospitals of five different cities in Poland were analyzed. They expressed several TEM-type ESBLs, TEM-4, TEM-29, TEM-85, TEM-86, TEM-93, and TEM-94. TEM-85 (L21F, R164S, E240K, T265M), TEM-86 (L21F, R164S, A237T, E240K, T265M), TEM-93 (M182T, G238S, E240K), and TEM-94 (L21F, E104K, M182T, G238S, T265M) were identified for the first time. Including the enzymes described earlier, TEM-47, TEM-48, TEM-49, and TEM-68, the group of known ESBLs of the TEM family produced by enterobacteria in Polish hospitals has increased to 10 variants. Comparative sequence analysis of the genes coding for all these β-lactamases revealed a view of their possible evolution, which, apart from the gradual acquisition of various mutations, could also have involved recombination events. Two different
bla
TEM-1
gene alleles were precursors of the ESBL genes:
bla
TEM-1A
, which was the ancestor of
bla
TEM-93
, and
bla
TEM-1F
, from which all the remaining genes originated. The evolution of the
bla
TEM-1F
-related genes most probably consisted of three major separate lineages, one of which, including
bla
TEM-4
,
bla
TEM-47
,
bla
TEM-48
,
bla
TEM-49
,
bla
TEM-68
, and
bla
TEM-94
, was highly structured itself and could have been initiated by the
bla
TEM-25
gene, identified exclusively in France so far. Plasmid fingerprinting analysis revealed a high degree of diversity of plasmids carrying related
bla
TEM
genes, which suggested either the intense diversification or transposition of
bla
TEM
genes between different plasmids or some contribution of convergent evolution. The results of this study clearly demonstrate that the environment of Polish hospitals has been highly favorable for the rapid evolution of ESBLs.
Mechanism of Action of a Novel Series of Naphthyridine-Type Ribosome Inhibitors: Enhancement of tRNA Footprinting at the Decoding Site of 16S rRNA
Authors: Shen Linus L. , Black-Schaefer Candace , Cai Yingna , Dandliker Peter J. , Beutel Bruce A. 
Published: April 2005

ABSTRACT

The novel ribosome inhibitors (NRIs) are a broad-spectrum naphthyridine class that selectively inhibits bacterial protein synthesis (P. J. Dandliker et al., Antimicrob. Agents Chemother. 47:3831-3839, 2003). Footprinting experiments, using a range of NRIs and chemical modification agents on
Escherichia coli
ribosomes, revealed no evidence for direct protection of rRNA. In the presence of tRNA, however, we found that NRIs enhanced the known ribosomal footprinting pattern of tRNA in a dose-dependent manner. The most prominent increase in protection, at A1492/3 and A1413 in helix-44 of 16S RNA, strictly required the presence of tRNA and poly(U), and the effect was correlated with the potency of the inhibitor. Radioligand binding studies with inhibitor [
3
H]A-424902 showed that the compound binds to tRNA, either in its charged or uncharged form. The dissociation constant for [
3
H]A-424902 binding to Phe-tRNA
Phe
was determined to be 1.8 μM, near its translation inhibition potency of 1.6 μM in a cell-free
S. pneumoniae
extract assay. The compound did not change the binding of radiolabeled tRNA to the 30S ribosomal subunit. Taken together, these results imply that the NRIs exert their effects on protein synthesis by structurally perturbing the tRNA/30S complex at the decoding site.
Selective Intracellular Activation of a Novel Prodrug of the Human Immunodeficiency Virus Reverse Transcriptase Inhibitor Tenofovir Leads to Preferential Distribution and Accumulation in Lymphatic Tissue
Authors: Lee William A. , He Gong-Xin , Eisenberg Eugene , Cihlar Tomas , Swaminathan Swami , Mulato Andrew , Cundy Kenneth C. 
Published: April 2005

ABSTRACT

An isopropylalaninyl monoamidate phenyl monoester prodrug of tenofovir (GS 7340) was prepared, and its in vitro antiviral activity, metabolism, and pharmacokinetics in dogs were determined. The 50% effective concentration (EC
50
) of GS 7340 against human immunodeficiency virus type 1 in MT-2 cells was 0.005 μM compared to an EC
50
of 5 μM for the parent drug, tenofovir. The (
L
)-alaninyl analog (GS 7340) was >1,000-fold more active than the (
D
)-alaninyl analog. GS 7340 has a half-life of 90 min in human plasma at 37°C and a half-life of 28.3 min in an MT-2 cell extract at 37°C. The antiviral activity (>10× the EC
50
) and the metabolic stability in MT-2 cell extracts (>35×) and plasma (>2.5×) were also sensitive to the stereochemistry at the phosphorus. After a single oral dose of GS 7340 (10 mg-eq/kg tenofovir) to male beagle dogs, the plasma bioavailability of tenofovir compared to an intravenous dose of tenofovir was 17%. The total intracellular concentration of all tenofovir species in isolated peripheral blood mononuclear cells at 24 h was 63 μg-eq/ml compared to 0.2 μg-eq/ml in plasma. A radiolabeled distribution study with dogs resulted in an increased distribution of tenofovir to tissues of lymphatic origin compared to the commercially available prodrug tenofovir DF (Viread).
Dual Targeting of Topoisomerase IV and Gyrase To Reduce Mutant Selection: Direct Testing of the Paradigm by Using WCK-1734, a New Fluoroquinolone, and Ciprofloxacin
Authors: Strahilevitz Jacob , Hooper David C. 
Published: April 2005

ABSTRACT

Quinolones that act equally against DNA gyrase and topoisomerase IV are a desirable modality to decrease the selection of resistant strains. We first determined by genetic and biochemical studies in
Staphylococcus aureus
that the primary target enzyme of WCK-1734, a new quinolone, was DNA gyrase. A single mutation in gyrase, but not topoisomerase IV, caused a two- to fourfold increase in the MIC. Studies with purified topoisomerase IV and gyrase from
S. aureus
also showed that gyrase was more sensitive than topoisomerase IV to WCK-1734 (50% inhibitory concentration, 1.25 and 2.5 to 5.0 μg/ml, respectively; 50% stimulation of cleavage complex formation, 0.62 and 2.5 to 5.0 μg/ml, respectively). To test the effect of balanced activity of quinolones against the two target enzymes, we measured the frequency of selection of mutants with ciprofloxacin (which targets topoisomerase IV) and WCK-1734 alone and in combination. With the combination of ciprofloxacin and WCK-1734, each at its MIC, the ratio of frequency of mutants selected was significantly lower than that with each drug alone at two times their respective MICs. We further characterized resistant strains selected with the combination of ciprofloxacin and WCK-1734 and found evidence to suggest the existence of novel mutational mechanisms for low-level quinolone resistance. By use of a combination of differentially targeting quinolones, this study provides novel data in direct support of the paradigm for dual targeting of quinolone action and reduced development of resistance.
Role of the ABC Transporter MRPA (PGPA) in Antimony Resistance in
Leishmania infantum
Axenic and Intracellular Amastigotes
Authors: El Fadili Karima , Messier Nadine , Leprohon Philippe , Roy Gaétan , Guimond Chantal , Trudel Nathalie , Saravia Nancy G. , Papadopoulou Barbara , Légaré Danielle , Ouellette Marc 
Published: April 2005

ABSTRACT

Antimonial compounds are the mainstay for the treatment of infections with the protozoan parasite
Leishmania
. We present our studies on
Leishmania infantum
amastigote parasites selected for resistance to potassium antimonyl tartrate [Sb(III)]. Inside macrophages, the Sb(III)-selected cells are cross-resistant to sodium stibogluconate (Pentostam), the main drug used against
Leishmania
. Putative alterations in the level of expression of more than 40 genes were compared between susceptible and resistant axenic amastigotes using customized DNA microarrays. The expression of three genes coding for the ABC transporter MRPA (PGPA),
S
-adenosylhomocysteine hydrolase, and folylpolyglutamate synthase was found to be consistently increased. The levels of cysteine were found to be increased in the mutant. Transfection of the
MRPA
gene was shown to confer sodium stibogluconate resistance in intracellular parasites. This MRPA-mediated resistance could be reverted by using the glutathione biosynthesis-specific inhibitor buthionine sulfoximine. These results highlight for the first time the role of MRPA in antimony resistance in the amastigote stage of the parasite and suggest a strategy for reversing resistance.
Altered PBP 2A and Its Role in the Development of Penicillin, Cefotaxime, and Ceftriaxone Resistance in a Clinical Isolate of
Streptococcus pneumoniae
Authors: Smith Anthony M. , Feldman Charles , Massidda Orietta , McCarthy Kerrigan , Ndiweni Dalu , Klugman Keith P. 
Published: April 2005

ABSTRACT

We report the unusual involvement of altered PBP 2A in the development of β-lactam resistance in
Streptococcus pneumoniae
. This was investigated amid three identical serotype 14 isolates (designated isolates 1, 2, and 3, respectively) of pneumococci cultured successfully from the blood of a human immunodeficiency virus-seropositive child with recurrent pneumonia. The passage of this strain through its human host induced several changes in the bacterium, which is typical of the adaptive and evolving nature of the pneumococcus. An efflux resistance mechanism, which conferred increased ciprofloxacin resistance, was induced in isolates 2 and 3. In addition, faster growth rates and larger capsules were also observed for these isolates, with respect to isolate 1. Notably, compared to isolates 1 and 2, isolate 3 showed a decrease in penicillin, cefotaxime, and ceftriaxone resistance. This change was associated with the replacement of an altered PBP 2A for an unaltered PBP 2A. In all likelihood, these events produced a strain which evolved into a fitter and more virulent type, isolate 3, that resulted in an aggravated pneumococcal infection and ultimately in the patient's death.
Novel Human Immunodeficiency Virus Type 1 Protease Mutations Potentially Involved in Resistance to Protease Inhibitors
Authors: Svicher Valentina , Ceccherini-Silberstein Francesca , Erba Fulvio , Santoro Maria , Gori Caterina , Bellocchi Maria Concetta , Giannella Sara , Trotta Maria Paola , Monforte Antonella d'Arminio , Antinori Andrea , Perno Carlo Federico 
Published: April 2005

ABSTRACTPlasma-derived sequences of human immunodeficiency virus type 1 (HIV-1) protease from 1,162 patients (457 drug-naïve patients and 705 patients receiving protease inhibitor [PI]-containing antiretroviral regimens) led to the identification and characterization of 17 novel protease mutations potentially associated with resistance to PIs. Fourteen mutations were positively associated with PIs and significantly correlated in pairs and/or clusters with known PI resistance mutations, suggesting their contribution to PI resistance. In particular, E34Q, K43T, and K55R, which were associated with lopinavir treatment, correlated with mutations associated with lopinavir resistance (E34Q with either L33F or F53L, or K43T with I54A) or clustered with multi-PI resistance mutations (K43T with V82A and I54V or V82A, V32I, and I47V, or K55R with V82A, I54V, and M46I). On the other hand, C95F, which was associated with treatment with saquinavir and indinavir, was highly expressed in clusters with either L90M and I93L or V82A and G48V. K45R and K20T, which were associated with nelfinavir treatment, were specifically associated with D30N and N88D and with L90M, respectively. Structural analysis showed that several correlated positions were within 8 Å of each other, confirming the role of the local environment for interactions among mutations. We also identified three protease mutations (T12A, L63Q, and H69N) whose frequencies significantly decreased in PI-treated patients compared with that in drug-naïve patients. They never showed positive correlations with PI resistance mutations; if anything, H69N showed a negative correlation with the compensatory mutations M36I and L10I. These mutations may prevent the appearance of PI resistance mutations, thus increasing the genetic barrier to PI resistance. Overall, our study contributes to a better definition of protease mutational patterns that regulate PI resistance and strongly suggests that other (novel) mutations beyond those currently known to confer resistance should be taken into account to better predict resistance to antiretroviral drugs.
Mechanistic Study of the Photodynamic Inactivation of
Candida albicans
by a Cationic Porphyrin
Authors: Lambrechts S. A. G. , Aalders M. C. G. , Van Marle J. 
Published: April 2005

ABSTRACT

The growing resistance against antifungal agents has renewed the search for alternative treatment modalities, and antimicrobial photodynamic inactivation (PDI) is a potential candidate. The cationic porphyrin 5-phenyl-10,15,20-Tris(
N
-methyl-4-pyridyl)porphyrin chloride (TriP[4]) is a photosensitizer that in combination with light can inactivate bacteria, fungi, and viruses. For future improvement of the efficacy of PDI of clinically relevant fungi such as
Candida albicans
, we sought to understand the working mechanism by following the response of
C. albicans
exposed to PDI using fluorescence confocal microscopy and freeze-fracture electron microscopy. The following events were observed under dark conditions: TriP[4] binds to the cell envelope of
C. albicans
, and none or very little TriP[4] enters the cell. Upon illumination the cell membrane is damaged and eventually becomes permeable for TriP[4]. After lethal membrane damage, a massive influx of TriP[4] into the cell occurs. Only the vacuole membrane is resistant to PDI-induced damage once TriP[4] passes the plasma membrane. Increasing the incubation time of
C. albicans
with TriP[4] prior to illumination did not increase the influx of TriP[4] into the cell or the efficacy of PDI. After the replacement of 100% phosphate-buffered saline (PBS) by 10% PBS as the medium,
C. albicans
became permeable for TriP[4] during dark incubation and the efficacy of PDI increased dramatically. In conclusion,
C. albicans
can be successfully inactivated by the cationic porphyrin TriP[4], and the cytoplasmic membrane is the target organelle. TriP[4] influx occurred only after cell death.
Targeting Tn
5
Transposase Identifies Human Immunodeficiency Virus Type 1 Inhibitors
Authors: Ason Brandon , Knauss Daniel J. , Balke Allison M. , Merkel George , Skalka Anna Marie , Reznikoff William S. 
Published: April 2005

ABSTRACT

Human immunodeficiency virus (HIV) type 1 (HIV-1) integrase is an underutilized drug target for the treatment of HIV infection. One limiting factor is the lack of costructural data for use in the rational design or modification of integrase inhibitors. Tn
5
transposase is a structurally well characterized, related protein that may serve as a useful surrogate. However, little data exist on inhibitor cross-reactivity. Here we screened 16,000 compounds using Tn
5
transposase as the target and identified 20 compounds that appear to specifically inhibit complex assembly. Six were found to also inhibit HIV-1 integrase. These compounds likely interact with a highly conserved region presumably within the catalytic core. Most promising, several cinnamoyl derivatives were found to inhibit HIV transduction in cells. The identification of integrase inhibitors from a screen using Tn
5
transposase as the target illustrates the utility of Tn
5
as a surrogate for HIV-1 integration even though the relationship between the two systems is limited to the active site architecture and catalytic mechanism.
Replication Fitness and NS5B Drug Sensitivity of Diverse Hepatitis C Virus Isolates Characterized by Using a Transient Replication Assay
Authors: Ludmerer Steven W. , Graham Donald J. , Boots Evelyn , Murray Edward M. , Simcoe Amy , Markel Eric J. , Grobler Jay A. , Flores Osvaldo A. , Olsen David B. , Hazuda Daria J. , LaFemina Robert L. 
Published: April 2005

ABSTRACT
The innate genetic variability characteristic of chronic hepatitis C virus (HCV) infection makes drug resistance a concern in the clinical development of HCV inhibitors. To address this, a transient replication assay was developed to evaluate the replication fitness and the drug sensitivity of NS5B sequences isolated from the sera of patients with chronic HCV infection. This novel assay directly compares replication between NS5B isolates, thus bypassing the potential sequence and metabolic differences which may arise with independent replicon cell lines. Patient-derived NS5B sequences were similar to those of the established HCV genotypes, but isolates from each patient shared genetic variability specific to that patient, with additional genetic variability observed across the individual isolates. Every sample provided functional NS5B isolates which supported subgenomic replication, frequently to levels comparable to that of laboratory-optimized replicons. All isolates were equivalently sensitive to an active-site nucleoside inhibitor, but the sensitivities to a panel of nonnucleoside inhibitors which targeted three distinct sites on NS5B varied among the isolates. In con1, the original laboratory-optimized replicon, the NS5B S282T substitution confers resistance to the nucleoside inhibitor but impairs replication. This substitution was engineered into both genotype 1a and genotype 1b isolates. Replication was severely debilitated, demonstrating that no compensatory residues were encoded within these genetically diverse sequences to increase the replication fitness of the mutated replicons. This work describes a transient replicon-based assay that can support the clinical development of compounds which target NS5B and demonstrates its utility by examining several patient-derived NS5B isolates for replication fitness and differential sensitivity to NS5B inhibitors.
Hypermutable and Fluoroquinolone-Resistant Clinical Isolates of
Staphylococcus aureus
Authors: Trong Hiep N'Guyen , Prunier Anne-Laure , Leclercq Roland 
Published: April 2005

ABSTRACT

Over 124 methicillin-susceptible
Staphylococcus aureus
0/74 fluoroquinolone-susceptible versus 5/50 fluoroquinolone-resistant isolates were hypermutable. Hypermutable isolates combined mutations in
gyrA
,
parC
, and/or
parE
genes. One strain had a large deletion of the mutator
mutS
and
mutL
genes. No relevant mutation in
mutS
and
mutL
genes was found in the other isolates.
Origin and Dissemination of Chloroquine-Resistant
Plasmodium falciparum
with Mutant
pfcrt
Alleles in the Philippines
Authors: Chen Nanhua , Wilson Danny W. , Pasay Cielo , Bell David , Martin Laura B. , Kyle Dennis , Cheng Qin 
Published: April 2005

ABSTRACT

The
pfcrt
allelic type and adjacent microsatellite marker type were determined for 82
Plasmodium falciparum
isolates from the Philippines. Mutant
pfcrt
allelic types P1a and P2a/P2b were dominant in different locations. Microsatellite analysis revealed that P2a/P2b evolved independently in the Philippines, while P1a shared common ancestry with Papua New Guinea chloroquine-resistant parasites.
Florfenicol Resistance Gene
floR
Is Part of a Novel Transposon
Authors: Doublet Benoît , Schwarz Stefan , Kehrenberg Corinna , Cloeckaert Axel 
Published: April 2005

ABSTRACT

The florfenicol/chloramphenicol resistance gene
floR
was found to be part of the novel 4,284-bp transposon Tn
floR
from
Escherichia coli
. Tn
floR
consists of the gene
floR
, a putative regulatory gene, and the transposase gene
tnpA
. A circular form of Tn
floR
was detected and suggested the potential mobility of this transposon.
Differences in Interactions between Azole Drugs Related to Modifications in the 14-α Sterol Demethylase Gene (
cyp51A
) of
Aspergillus fumigatus
Authors: Garcia-Effron G. , Mellado E. , Gomez-Lopez A. , Alcazar-Fuoli L. , Cuenca-Estrella M. , Rodriguez-Tudela Juan L. 
Published: April 2005

ABSTRACT

The combined activity of different azole drugs was investigated. Thirty-one
Aspergillus fumigatus
strains were tested, including two
cyp51A
−
and one
cyp51B
−
gene-knockout strain and azole-susceptible and -resistant strains with different resistance mechanisms. The combination of itraconazole and voriconazole was synergistic for all strains except for those with gene knockouts.