bluuebunny/crossref_metadata_2025_split huggingface dataset:
Potent Anti-Influenza Activity of Cyanovirin-N and Interactions with Viral Hemagglutinin
Authors: O'Keefe Barry R. , Smee Donald F. , Turpin Jim A. , Saucedo Carrie J. , Gustafson Kirk R. , Mori Toshiyuki , Blakeslee Dennis , Buckheit Robert , Boyd Michael R. 
Published: July 2003

ABSTRACT

The novel antiviral protein cyanovirin-N (CV-N) was initially discovered based on its potent activity against the human immunodeficiency virus (HIV). Subsequent studies identified the HIV envelope glycoproteins gp120 and gp41 as molecular targets of CV-N. More recently, mechanistic studies have shown that certain high-mannose oligosaccharides (oligomannose-8 and oligomannose-9) found on the HIV envelope glycoproteins comprise the specific sites to which CV-N binds. Such selective, carbohydrate-dependent interactions may account, at least in part, for the unusual and unexpected spectrum of antiviral activity of CV-N described herein. We screened CV-N against a broad range of respiratory and enteric viruses, as well as flaviviruses and herpesviruses. CV-N was inactive against rhinoviruses, human parainfluenza virus, respiratory syncytial virus, and enteric viruses but was moderately active against some herpesvirus and hepatitis virus (bovine viral diarrhea virus) strains (50% effective concentration [EC
50
] = ∼1 μg/ml) while inactive against others. Remarkably, however, CV-N and related homologs showed highly potent antiviral activity against almost all strains of influenza A and B virus, including clinical isolates and a neuraminidase inhibitor-resistant strain (EC
50
= 0.004 to 0.04 μg/ml). When influenza virus particles were pretreated with CV-N, viral titers were lowered significantly (>1,000-fold). Further studies identified influenza virus hemagglutinin as a target for CV-N, showed that antiviral activity and hemagglutinin binding were correlated, and indicated that CV-N′s interactions with hemagglutinin involved oligosaccharides. These results further reveal new potential avenues for antiviral therapeutics and prophylaxis targeting specific oligosaccharide-comprised sites on certain enveloped viruses, including HIV, influenza virus, and possibly others.
Unique Biological Properties and Molecular Mechanism of 5,6-Bridged Quinolones
Authors: Macinga David R. , Renick Paul J. , Makin Kelly M. , Ellis David H. , Kreiner Allison A. , Li Min , Rupnik Kirk J. , Kincaid Erica M. , Wallace Cynthia D. , Ledoussal Benoit , Morris Timothy W. 
Published: July 2003

ABSTRACT

We have characterized an early series of 5,6-bridged dioxinoquinolones which behaved strikingly different from typical quinolones. The 5,6-bridged dioxinoquinolones inhibited
Escherichia coli
DNA gyrase supercoiling activity but, unlike typical quinolones, failed to stimulate gyrase-dependent cleavable complex formation. Analogous unsubstituted compounds stimulated cleavable complex formation but were considerably less potent than the corresponding 5,6-bridged compounds. Consistent with a previous report (M. Antoine et al., Chim. Ther. 7:434-443, 1972) and contrary to established quinolone SAR trends, a compound with an N-1 methyl substitution (PGE-8367769) was more potent than its analog with an N-1 ethyl substitution (PGE-6596491). PGE-8367769 was shown to antagonize ciprofloxacin-mediated cleavable complex formation in a dose-dependent manner, suggesting an interaction with the gyrase-DNA complex that overlaps that of ciprofloxacin. Resistance to PGE-8367769 in
E. coli
was found to arise through missense mutations in
gyrA
, implicating DNA gyrase as the primary antibacterial target. Notably, only 1 of 15 distinct mutations selected on PGE-8367769 (D87G) has previously been implicated in quinolone resistance in
E. coli.
The remaining 14 mutations (E16V, G31V, R38L, G40A, Y50D, V70A, A84V, I89L, M135T, G173S, T180I, F217C, P218T, and F513C) have not been previously reported, and most were located outside of the traditional quinolone resistance-determining region. These novel GyrA mutations decreased sensitivity to 5,6-bridged dioxinoquinolones by four- to eightfold, whereas they did not confer resistance to other quinolones such as ciprofloxacin, clinafloxacin, or nalidixic acid. These results demonstrate that the 5,6-bridged quinolones act via a mechanism that is related to but qualitatively different from that of typical quinolones.
Correlation of Daptomycin Bactericidal Activity and Membrane Depolarization in
Staphylococcus aureus
Authors: Silverman Jared A. , Perlmutter Nancy G. , Shapiro Howard M. 
Published: July 2003

ABSTRACT

The objective of this study was to further elucidate the role of membrane potential in the mechanism of action of daptomycin, a novel lipopeptide antibiotic. Membrane depolarization was measured by both fluorimetric and flow cytometric assays. Adding daptomycin (5 μg/ml) to
Staphylococcus aureus
gradually dissipated membrane potential. In both assays, cell viability was reduced by >99% and membrane potential was reduced by >90% within 30 min of adding daptomycin. Cell viability decreased in parallel with changes in membrane potential, demonstrating a temporal correlation between bactericidal activity and membrane depolarization. Decreases in viability and potential also showed a dose-dependent correlation. Depolarization is indicative of ion movement across the cytoplasmic membrane. Fluorescent probes were used to demonstrate Ca
2+
-dependent, daptomycin-triggered potassium release from
S. aureus
. Potassium release was also correlated with bactericidal activity. This study demonstrates a clear correlation between dissipation of membrane potential and the bactericidal activity of daptomycin. A multistep model for daptomycin's mechanism of action is proposed.
Subinhibitory Concentrations of the Deformylase Inhibitor Actinonin Increase Bacterial Release of Neutrophil-Activating Peptides: a New Approach to Antimicrobial Chemotherapy
Authors: Fu Huamei , Dahlgren Claes , Bylund Johan 
Published: July 2003

ABSTRACT

Bacterial protein synthesis starts with a formylated methionine residue, and this residue is sequentially cleaved away by a unique peptide deformylase (PDF) and a methionine aminopeptidase to generate mature proteins. The formylation-deformylation of proteins is a unique hallmark of bacterial metabolism and has recently become an attractive target for the development of antimicrobial agents. The innate immune system uses the formylation of bacterial proteins as a target, and professional phagocytes, e.g., neutrophils, express specific receptors for bacterium-derived formylated peptides. Activation of formyl peptide receptors (FPR) mediates neutrophil migration and the release of oxygen radicals and other antimicrobial substances from these cells. We hypothesize that the use of a PDF inhibitor would increase the production of proinflammatory peptides from the bacteria and thus trigger a more pronounced innate immune response. We tested this hypothesis by exposing
Escherichia coli
to subinhibitory doses of the PDF inhibitor actinonin and show that actinonin indeed increases the production and secretion of neutrophil-activating peptides that activate human neutrophils through FPR. These findings could be potentially used as a new approach to antibacterial chemotherapy.
Haemophilus influenzae bla
ROB-1
Mutations in Hypermutagenic Δ
ampC Escherichia coli
Conferring Resistance to Cefotaxime and β-Lactamase Inhibitors and Increased Susceptibility to Cefaclor
Authors: Galán Juan-Carlos , Morosini María-Isabel , Baquero María-Rosario , Reig Milagro , Baquero Fernando 
Published: July 2003

ABSTRACT

The clinical use of cefaclor has been shown to enrich
Haemophilus influenzae
populations harboring cefaclor-hydrolyzing ROB-1 β-lactamase. Such a selective process may lead to the increased use of extended-spectrum cephalosporins or β-lactams plus β-lactamase inhibitors and, eventually, resistance to these agents, which has not previously been observed in
H. influenzae
. In order to establish which
bla
ROB-1
mutations, if any, could confer resistance to extended-spectrum cephalosporins and/or to β-lactamase inhibitors, a plasmid harboring
bla
ROB-1
was transformed into hypermutagenic strain
Escherichia coli
GB20 (Δ
ampC mutS
::Tn
10
), and this construct was used in place of
H. influenzae bla
ROB-1
. Strain GB20 with the cloned gene was submitted to serial passages in tubes containing broth with increasing concentrations of selected β-lactams (cefotaxime or amoxicillin-clavulanate). Different mutations in the
bla
ROB-1
gene were obtained during the passages in the presence of the different concentrations of the selective agents. Mutants resistant to extended-spectrum cephalosporins harbored either the Leu169→Ser169 or the Arg164→Trp164 substitution or the double amino acid change Arg164→Trp164 and Ala237→Thr237. ROB-1 mutants that were resistant to β-lactams plus β-lactamase inhibitors and that harbored the Arg244→Cys244 or the Ser130→Gly130 replacement were also obtained. The cefaclor-hydrolyzing efficiencies of the ROB-1 variants were strongly decreased in all mutants, suggesting that if
bla
ROB-1
mutants were selected by cefaclor, this drug would prevent the further evolution of this β-lactamase toward molecular forms able to resist extended-spectrum cephalosporins or β-lactamase inhibitors.
MsrR, a Putative Cell Envelope-Associated Element Involved in
Staphylococcus aureus sarA
Attenuation
Authors: Rossi Jutta , Bischoff Markus , Wada Akihito , Berger-Bächi Brigitte 
Published: July 2003

ABSTRACT

A novel membrane-associated protein, MsrR, was identified in
Staphylococcus aureus
which affects resistance to methicillin and teicoplanin, as well as the synthesis of virulence factors. MsrR belongs to the LytR-CpsA-Psr family of cell envelope-related transcriptional attenuators and was shown to be inducible by cell wall-active agents, such as β-lactams, glycopeptides, and lysostaphin. The expression of
msrR
peaked in the early exponential growth phase and decreased sharply thereafter.
msrR
mutants showed increased
sarA
transcription and an earlier and higher expression of RNAIII, resulting in altered expression of virulence factors such as alpha-toxin and protein A. These observations suggest that MsrR is a new component involved in
sarA
attenuation and the regulatory network controlling virulence gene expression in
S. aureus
.
Plasmid-Mediated High-Level Resistance to Aminoglycosides in
Enterobacteriaceae
Due to 16S rRNA Methylation
Authors: Galimand Marc , Courvalin Patrice , Lambert Thierry 
Published: July 2003

ABSTRACT

A self-transferable plasmid of ca. 80 kb, pIP1204, conferred multiple-antibiotic resistance to
Klebsiella pneumoniae
BM4536, which was isolated from a urinary tract infection. Resistance to β-lactams was due to the
bla
TEM1
and
bla
CTX-M
genes, resistance to trimethroprim was due to the
dhfrXII
gene, resistance to sulfonamides was due to the
sul1
gene, resistance to streptomycin-spectinomycin was due to the
ant3"9
gene, and resistance to nearly all remaining aminoglycosides was due to the
aac3-II
gene and a new gene designated
armA
(aminoglycoside resistance methylase). The cloning of
armA
into a plasmid in
Escherichia coli
conferred to the new host high-level resistance to 4,6-disubstituted deoxystreptamines and fortimicin. The deduced sequence of ArmA displayed from 37 to 47% similarity to those of 16S rRNA m
7
G methyltransferases from various actinomycetes, which confer resistance to aminoglycoside-producing strains. However, the low guanine-plus-cytosine content of
armA
(30%) does not favor an actinomycete origin for the gene. It therefore appears that posttranscriptional modification of 16S rRNA can confer high-level broad-range resistance to aminoglycosides in gram-negative human pathogens.
Extended-Spectrum β-Lactamases in Ireland, Including a Novel Enzyme, TEM-102
Authors: Morris Dearbháile , O'Hare Colette , Glennon Maura , Maher Majella , Corbett-Feeney Geraldine , Cormican Martin 
Published: July 2003

ABSTRACT

Organisms producing extended-spectrum β-lactamases (ESBLs) have been reported in many countries, but there is no information on the prevalence of ESBL-producing members of the family
Enterobacteriaceae
in Ireland. A total of 925 isolates of ampicillin-resistant members of the
Enterobacteriaceae
were received from six hospitals in Ireland over a 3-year period from September 1996 to September 1999. Isolates were screened for ESBL production by the double-disk diffusion (DDD) method. DDD-positive isolates that were (i) confirmed as ESBL producers by National Committee for Clinical Laboratory Standards (NCCLS) confirmatory testing and (ii) susceptible to cefoxitin by disk diffusion were considered ESBL producers. By these criteria, 27 (3%) of the ampicillin-resistant members of the
Enterobacteriaceae
studied were categorized as ESBL producers. Molecular typing suggested that some intra- and interhospital spread of ESBL-producing isolates had occurred. DNA sequencing of amplified
bla
TEM
and
bla
SHV
genes resulted in the detection of a novel
bla
TEM
ESBL gene,
bla
TEM-102
in two isolates (
Klebsiella pneumoniae
and
Enterobacter cloacae
) received from the same hospital but isolated from different patients. The study suggests dissemination of ESBL-producing bacteria within the health care system in Ireland and emphasizes the need for measures to control such spread.
TransferablevanB2Tn5382-Containing Elements in Fecal Streptococcal Strains from Veal Calves
Authors: Dahl Kristin H. , Sundsfjord Arnfinn 
Published: July 2003

ABSTRACTThree vancomycin-resistant veal calf fecal streptococci, identified asStreptococcus gallolyticus(n= 2) andStreptococcus lutetiensis, were shown to harborvanB2Tn5382-like elements earlier described in enterococci. OneS. gallolyticusstrain had a 1,495-bp IS256-related element inserted invanSB. ThevanB2Tn5382element present in the plasmid-freeS. lutetiensisstrain was transferable toEnterococcus faeciumBM4105-RF,Enterococcus faecalisJH2-2, and its recombination-deficient derivative, UV202. The transfer frequencies were comparable between recipient strains (from 1 × 10−7to 7 × 10−6). All transconjugants acquired avanB-containing chromosomal insert of approximately 100 kb, apparently by site-specific integration. Secondary transconjugants were not observed in intraspecies retransfer experiments. These observations are consistent with a conjugative, selftransmissible, integrative element that might be involved in the interspecies spread ofvanB2resistance determinants. Two JH2-2-derived transconjugants had also gained additional copies of largevanB-containing chromosomal fragments, a process that involves unexplained mechanisms that seems to require functional host cell-dependent recombination mechanisms.
Heme Binding Contributes to Antimalarial Activity of Bis-Quaternary Ammoniums
Authors: Biagini Giancarlo A. , Richier Eric , Bray Patrick G. , Calas Michèle , Vial Henri , Ward Stephen A. 
Published: July 2003

ABSTRACT

Quaternary ammonium compounds have received recent attention due to their potent in vivo antimalarial activity based on their ability to inhibit de novo phosphatidylcholine synthesis. Here we show that in addition to this, heme binding significantly contributes to the antimalarial activity of these compounds. For the study, we used a recently synthesized bis-quaternary ammonium compound, T16 (1,12-dodecanemethylene bis[4-methyl-5-ethylthiazolium] diodide), which exhibits potent antimalarial activity (50% inhibitory concentration, ∼25 nM). Accumulation assays reveal that this compound is readily concentrated several hundredfold (cellular accumulation ratio, ∼500) into parasitized erythrocytes. Approximately 80% of the drug was shown to be distributed within the parasite, ∼50% of which was located in the parasite food vacuoles. T16 uptake was affected by anion substitution (permeation increasing in the order Cl
−
< Br
−
= NO
3
−
< I
−
< SCN
−
) and was sensitive to furosemide—properties similar to substrates of the induced new permeability pathway in infected erythrocytes. Scatchard plot analysis of in situ T16 binding revealed high-affinity and low-affinity binding sites. The high-affinity binding site

K
d

was similar to that measured in vitro for T16 and ferriprotoporphyrin IX (FPIX) binding. Significantly, the capacity but not the

K
d

of the high-affinity binding site was decreased by reducing the concentration of parasite FPIX. Decreasing the parasite FPIX pool also caused a marked antagonism of T16 antimalarial activity. In addition, T16 was also observed to associate with parasite hemozoin. Binding of T16 to FPIX in the digestive food vacuole is shown to be critical for drug accumulation and antimalarial activity. These data provide additional new mechanisms of antimalarial activity for this promising new class of antimalarial compounds.
Potent Inhibitors of
Plasmodium
Phospholipid Metabolism with a Broad Spectrum of In Vitro Antimalarial Activities
Authors: Ancelin Marie L. , Calas Michèle , Vidal-Sailhan Valérie , Herbuté Serge , Ringwald Pascal , Vial Henri J. 
Published: July 2003

ABSTRACT

We characterized the potent in vitro antimalarial activity and biologic assessment of 13 phospholipid polar head analogs on a comparative basis. There was a positive relationship between the abilities of the drugs to inhibit parasite growth in culture and their abilities to specifically inhibit phosphatidylcholine biosynthesis of
Plasmodium falciparum
-infected erythrocytes. Maximal activity of G25 was observed for the trophozoite stage of the 48-h erythrocytic cycle (50% inhibitory concentration, 0.75 nM), whereas the schizont and ring stages were 12- and 213-fold less susceptible. The compounds exerted a rapid nonreversible cytotoxic effect, with complete clearance of parasitemia after 5 h of contact with the mature stages. The compounds were highly specific against
P. falciparum
, with much lower toxicity against three other mammalian cell lines, and the in vitro therapeutic indices ranged from 300 to 2,500,000. Finally, the monoquaternary ammonium E10 and two bis-ammonium salts, G5 and G25, were similarly active against multiresistant strains and fresh isolates of
P. falciparum
. This impressive selective in vitro toxicity against
P. falciparum
strongly highlights the clinical potential of these quaternary ammonium salts for malarial chemotherapy.
In Vivo Antimalarial Activities of Mono- and Bis Quaternary Ammonium Salts Interfering with
Plasmodium
Phospholipid Metabolism
Authors: Ancelin Marie L. , Calas Michèle , Bonhoure Anne , Herbute Serge , Vial Henri J. 
Published: July 2003

ABSTRACT

We previously showed that quaternary ammonium salts have potent antimalarial activities against the blood stage of drug-resistant
Plasmodium falciparum
. In the present study, 13 compounds of this series were comparatively assessed in murine in vivo malarial models. Mice infected with
Plasmodium berghei
were successfully treated with 11 quaternary ammonium salts in a 4-day suppressive test with a once-daily intraperitoneal administration. The dose required to decrease parasitemia by 50% (ED
50
) ranged from 0.04 to 4.5 mg/kg of body weight. For six mono- and three bis-quaternary ammonium salts, the therapeutic indices (i.e., 50% lethal dose and ED
50
) were higher than 5, and at best, around 20 to 30 for five of them (E6, E8, F4, G5, and G25), which is comparable to that of chloroquine under the same conditions.
Plasmodium chabaudi
was significantly more susceptible to G5, G15, and G25 compounds than
P. berghei
. Similar therapeutic indices were obtained, regardless of the administration mode or initial parasitemia (up to 11.2%). Parasitemia clearance was complete without recrudescence. Subcutaneously administered radioactive compounds had a short elimination half-life in mice (3.5 h) with low bioavailability (17.3%), which was likely due to the permanent cationic charge of the molecule. The high in vivo therapeutic index in the
P. chabaudi
-infected mouse model and the absence of recrudescence highlight the enormous potential of these quaternary ammonium salts for clinical malarial treatment.
Activities of Mutant Prevention Concentration-Targeted Moxifloxacin and Levofloxacin against
Streptococcus pneumoniae
in an In Vitro Pharmacodynamic Model
Authors: Allen George P. , Kaatz Glenn W. , Rybak Michael J. 
Published: July 2003

ABSTRACT

The differential effects of moxifloxacin and levofloxacin on the development of resistance in four
Streptococcus pneumoniae
isolates were examined by using an in vitro pharmacodynamic model. Therapeutic regimens (moxifloxacin: peak, 4.5 μg/ml; half-life [
t
1/2
], 12 h; and levofloxacin: peak, 6 μg/ml;
t
1/2
, 6 h) were tested against two fluoroquinolone-susceptible isolates (strains 79 and ATCC 49619) and KD2138 and KD2139 (
parC
and
gyrA
mutants, respectively, of ATCC 49619). Mutant prevention concentration (MPC)-targeted regimens with modified pharmacokinetics of each drug were simulated to match the area under the concentration-time curve (AUC) above the MPC for the two fluoroquinolones. Moxifloxacin MICs and MPCs (MIC/MPC) for isolates 79, ATCC 49619, KD2138, and KD2139, respectively, were 0.125 and 0.5, 0.125 and 0.5, 0.25 and 8, and 0.25 and 4 μg/ml. Levofloxacin MICs and MPCs for the same isolates were 1 and 4, 0.5 and 2, 1 and 64, and 0.5 and 32 μg/ml, respectively. Therapeutic levofloxacin concentrations led to isolation of mutants of ATCC 49619 (S79Y in ParC), KD2138 (S81Y in GyrA), and KD2139 (S79Y in ParC). Therapeutic moxifloxacin concentrations against the
gyrA
mutant KD2139 resulted in outgrowth of a mutant with a ParC substitution (S79Y) but caused no emergence of mutants of the other three isolates. MPC-targeted moxifloxacin (lower-than-normal peak = 0.75 to 1.5 μg/ml, administered at levofloxacin's
t
1/2
) caused growth of a GyrA variant (S81Y) of KD2138 and a ParC variant (S79Y) of KD2139, while no mutants of ATCC 49619 were recovered. MPC-targeted levofloxacin (higher-than-normal peak = 14.5 to 29.5 μg/ml, administered at moxifloxacin's
t
1/2
) against KD2138 and KD2139 did not prevent the development of the mutations observed in therapeutic regimens, but resistance in the fluoroquinolone-susceptible ATCC 49619 was no longer noted. Normalization of the respective AUC/MPC ratios of moxifloxacin and levofloxacin did not eliminate differences in resistance selectivity of the two agents in all cases. We conclude that the reduced recovery of resistant mutants of
S. pneumoniae
following moxifloxacin exposure compared to levofloxacin may be due to intrinsic differences between the drugs. Increasing the concentration and exposure (
t
1/2
) to exceed the MPC may prevent mutations from occurring in fluoroquinolone-susceptible strains. However, this strategy did not prevent the selection of secondary mutants in strains with preexisting mutations. Further study of the MPC concept to evaluate these relationships is warranted.