bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiple Antibiotic Resistance in
Stenotrophomonas maltophilia
: Involvement of a Multidrug Efflux System
Authors: Zhang Li , Li Xian-Zhi , Poole Keith 
Published: July 2002

ABSTRACT

Clinical strains of
Stenotrophomonas maltophilia
are often highly resistant to multiple antibiotics, although the mechanisms of resistance are generally poorly understood. Multidrug resistant (MDR) strains were readily selected by plating a sensitive reference strain of the organism individually onto a variety of antibiotics, including tetracycline, chloramphenicol, ciprofloxacin, and norfloxacin. Tetracycline-selected MDR strains typically showed cross-resistance to erythromycin and fluoroquinolones and, in some instances, aminoglycosides. MDR mutants selected with the other agents generally displayed resistance to chloramphenicol and fluoroquinolones only, although two MDR strains (e.g., K1385) were also resistant to erythromycin and hypersusceptible to aminoglycosides. Many of the MDR strains expressed either moderate or high levels of a novel outer membrane protein (OMP) of ca. 50 kDa molecular mass, a phenotype typical of MDR strains of
Pseudomonas aeruginosa
hyperexpressing drug efflux systems. Indeed, the 50-kDa OMP of these
S. maltophilia
MDR strains reacted with antibody to OprM, the outer membrane component of the MexAB-OprM MDR efflux system of
P. aeruginosa
. Similarly, a ca. 110-kDa cytoplasmic membrane protein of these MDR strains also reacted with antibody to the MexB component of the
P. aeruginosa
pump. The outer and cytoplasmic membranes of several clinical
S. maltophilia
strains also reacted with the anti-OprM and anti-MexB antibodies. N-terminal amino acid sequencing of a cyanogen bromide-generated peptide of the 50-kDa OMP of MDR strain K1385, dubbed SmeM (
Stenotrophomonas
multidrug efflux), revealed it to be very similar to a number of outer membrane multidrug efflux components of
P. aeruginosa
and
Pseudomonas putida
. Deletion of the L1 and L2 β-lactamase genes confirmed that these enzymes were responsible for the bulk of the β-lactam resistance of K1385 and its parent. Still, overexpression of the MDR efflux mechanism in an L1- and L2-deficient derivative of K1385 did yield a modest increase in resistance to a few β-lactams. These data are consistent with the MDR efflux mechanism(s) playing a role in the multidrug resistance of
S. maltophilia
.
Inhibition of Inositol Phosphorylceramide Synthase by Aureobasidin A in
Candida
and
Aspergillus
Species
Authors: Zhong Wenyan , Jeffries Matthew W. , Georgopapadakou Nafsika H. 
Published: July 2002

ABSTRACT

Inositol phosphorylceramide (IPC) synthase is an enzyme common to fungi and plants that catalyzes the transfer of phosphoinositol from phosphatidylinositol to ceramide to form IPC. The reaction is a key step in fungal sphingolipid biosynthesis and the target of the antibiotics galbonolide A, aureobasidin A, and khafrefungin. As a first step toward understanding the antifungal spectrum of IPC synthase inhibitors, we examined the sensitivity of IPC synthase to aureobasidin A in membrane preparations of
Candida
species (
Candida albicans
,
C. glabrata
,
C. tropicalis
,
C. parapsilosis
, and
C. krusei
) and
Aspergillus
species (
Aspergillus fumigatus
,
A. flavus
,
A. niger
, and
A. terreus
). As expected, preparations from the five
Candida
species, all exquisitely susceptible to aureobasidin A (MICs, <2 μg/ml), had IPC synthase activity (specific activity, 50 to 400 pmol/min/mg of protein) sensitive to aureobasidin A (50% inhibitory concentrations [IC
50
s], 2 to 4 ng/ml). Surprisingly, preparations from the four
Aspergillus
species, including
A. fumigatus
and
A. flavus
, which are intrinsically resistant to aureobasidin A (MICs, >50 μg/ml), had IPC synthase activity (specific activity, 1 to 3 pmol/min/mg of protein) also sensitive to aureobasidin A (IC
50
s, 3 to 5 ng/ml). The mammalian multidrug resistance modulators verapamil, chlorpromazine, and trifluoperazine lowered the MIC of aureobasidin A for
A. fumigatus
from >50 μg/ml to 2 to 3 μg/ml, suggesting that the resistance of this major fungal pathogen is the result of increased efflux.
Sodium Dodecyl Sulfate and C31G as Microbicidal Alternatives to Nonoxynol 9: Comparative Sensitivity of Primary Human Vaginal Keratinocytes
Authors: Krebs Fred C. , Miller Shendra R. , Catalone Bradley J. , Welsh Patricia A. , Malamud Daniel , Howett Mary K. , Wigdahl Brian 
Published: July 2002

ABSTRACT
A broad-spectrum vaginal microbicide must be effective against a variety of sexually transmitted disease pathogens and be minimally toxic to the cell types found within the vaginal epithelium, including vaginal keratinocytes. We assessed the sensitivity of primary human vaginal keratinocytes to potential topical vaginal microbicides nonoxynol-9 (N-9), C31G, and sodium dodecyl sulfate (SDS). Direct immunofluorescence and fluorescence-activated cell sorting analyses demonstrated that primary vaginal keratinocytes expressed epithelial cell-specific keratin proteins. Experiments that compared vaginal keratinocyte sensitivity to each agent during a continuous, 48-h exposure demonstrated that primary vaginal keratinocytes were almost five times more sensitive to N-9 than to either C31G or SDS. To evaluate the effect of multiple microbicide exposures on cell viability, primary vaginal keratinocytes were exposed to N-9, C31G, or SDS three times during a 78-h period. In these experiments, cells were considerably more sensitive to C31G than to N-9 or SDS at lower concentrations within the range tested. When agent concentrations were chosen to result in an endpoint of 25% viability after three daily exposures, each exposure decreased cell viability at the same constant rate. When time-dependent sensitivity during a continuous 48-h exposure was examined, exposure to C31G for 18 h resulted in losses in cell viability not caused by either N-9 or SDS until at least 24 to 48 h. Cumulatively, these results reveal important variations in time- and concentration-dependent sensitivity to N-9, C31G, or SDS within populations of primary human vaginal keratinocytes cultured in vitro. These investigations represent initial steps toward both in vitro modeling of the vaginal microenvironment and studies of factors that impact the in vivo efficacy of vaginal topical microbicides.
In Vitro and In Vivo Activities of SCH 56592 (Posaconazole), a New Triazole Antifungal Agent, against
Aspergillus
and
Candida
Authors: Cacciapuoti Anthony , Loebenberg David , Corcoran Erik , Menzel Fred , Moss Eugene L. , Norris Christine , Michalski Monika , Raynor Kimberly , Halpern Judith , Mendrick Cara , Arnold Brian , Antonacci Barry , Parmegiani Raulo , Yarosh-Tomaine Taisa , Miller George H. , Hare Roberta S. 
Published: July 2002

ABSTRACT

SCH 56592 (posaconazole), a new triazole antifungal agent, was tested in vitro, and its activity was compared to that of itraconazole against 39
Aspergillus
strains and to that of fluconazole against 275
Candida
and 9
Cryptococcus
strains. The SCH 56592 MICs for
Aspergillus
ranged from ≤0.002 to 0.5 μg/ml, and those of itraconazole ranged from ≤0.008 to 1 μg/ml. The SCH 56592 MICs for
Candida
and
Cryptococcus
strains ranged from ≤0.004 to 16 μg/ml, and those of fluconazole ranged from ≤0.062 to >64 μg/ml. SCH 56592 showed excellent activity against
Aspergillus fumigatus
and
Aspergillus flavus
in a pulmonary mouse infection model. When administered therapeutically, the 50% protective doses (PD
50
s) of SCH 56592 ranged from 3.6 to 29.9 mg/kg of body weight, while the PD
50
s of SCH 56592 administered prophylactically ranged from 0.9 to 9.0 mg/kg; itraconazole administered prophylactically was ineffective (PD
50
s, >75 mg/kg). SCH 56592 was also very efficacious against fluconazole-susceptible, -susceptible dose-dependent, or -resistant
Candida albicans
strains in immunocompetent or immunocompromised mouse models of systemic infection. The PD
50
s of SCH 56592 administered therapeutically ranged from 0.04 to 15.6 mg/kg, while the PD
50
s of SCH 56592 administered prophylactically ranged from 1.5 to 19.4 mg/kg. SCH 56592 has excellent potential for therapy against serious
Aspergillus
or
Candida
infections.
Comparative Activities of Ciprofloxacin, Clinafloxacin, Gatifloxacin, Gemifloxacin, Levofloxacin, Moxifloxacin, and Trovafloxacin against Epidemiologically Defined
Acinetobacter baumannii
Strains
Authors: Heinemann Barbara , Wisplinghoff Hilmar , Edmond Michael , Seifert Harald 
Published: July 2002

ABSTRACT

In vitro activities of seven fluoroquinolones against 140 clinical
Acinetobacter baumannii
isolates representing 138 different strain types were determined. The rank order of activity was clinafloxacin > gatifloxacin > levofloxacin > trovafloxacin > gemifloxacin = moxifloxacin > ciprofloxacin. The 31 outbreak-related
A. baumannii
strains were significantly more resistant than were 109 sporadic strains.
Sodium Stibogluconate (Pentostam) Potentiates Oxidant Production in Murine Visceral Leishmaniasis and in Human Blood
Authors: Rais Samira , Perianin Axel , Lenoir Monique , Sadak Abderrahim , Rivollet Daniele , Paul Muriel , Deniau Michele 
Published: July 2002

ABSTRACTSodium stibogluconate (Sbb), a leishmanicidal drug, was studied for its in vivo effect on the formation of reactive oxygen species (ROS), assessed by chemiluminescence (CL) in the whole blood of mice infected withLeishmania infantum. Stimulation of ROS formation induced ex vivo by zymosan particles or the protein kinase C activator phorbol myristate acetate (PMA) was reduced by approximately 25% (P< 0.05) after infection of mice. Treatment of infected mice with Sbb (50 to 400 mg/kg of body weight) enhanced the blood CL induced by zymosan and PMA (47 to 96%,P< 0.01). The drug potentiation effect also occurred in uninfected mice. In vitro treatment of normal human blood with Sbb (1, 10, or 100 μg/ml) for 1 h primed the CL response to PMA (29 to 54%). The priming effect of Sbb was also observed on the production of superoxide by isolated polymorphonuclear leukocytes stimulated either by PMA and zymosan or by the chemoattractantsN-formyl-Met-Leu-Phe and platelet-activating factor. These data provide the first evidence of priming of the phagocyte respiratory burst by Sbb. This novel property of Sbb may contribute to the drug's leishmanicidal effect.
Multiple Mutations Modulate the Function of Dihydrofolate Reductase in Trimethoprim-Resistant
Streptococcus pneumoniae
Authors: Maskell Jeffrey P. , Sefton Armine M. , Hall Lucinda M. C. 
Published: July 2002

ABSTRACT

Trimethoprim resistance in
Streptococcus pneumoniae
can be conferred by a single amino acid substitution (I100-L) in dihydrofolate reductase (DHFR), but resistant clinical isolates usually carry multiple DHFR mutations. DHFR genes from five trimethoprim-resistant isolates from the United Kingdom were compared to susceptible isolates and used to transform a susceptible control strain (CP1015). All trimethoprim-resistant isolates and transformants contained the I100-L mutation. The properties of DHFRs from transformants with different combinations of mutations were compared. In a transformant with only the I100-L mutation (R12/T2) and a D92-A mutation also found in the DHFRs of susceptible isolates, the enzyme was much more resistant to trimethoprim inhibition (50% inhibitory concentration [IC
50
], 4.2 μM) than was the DHFR from strain CP1015 (IC
50
, 0.09 μM). However,
K

m

values indicated a lower affinity for the enzyme's natural substrates (
K

m

for dihydrofolate [DHF], 3.1 μM for CP1015 and 27.5 μM for R12/T2) and a twofold decrease in the specificity constant. In transformants with additional mutations in the C-terminal portion of the enzyme,
K

m

values for DHF were reduced (9.2 to 15.2 μM), indicating compensation for the lower affinity generated by I100-L. Additional mutations in the N-terminal portion of the enzyme were associated with up to threefold-increased resistance to trimethoprim (IC
50
of up to 13.7 μM). It is postulated that carriage of the mutation M53-I—which, like I100-L, corresponds to a trimethoprim binding site in the
Escherichia coli
DHFR—is responsible for this increase. This study demonstrates that although the I100-L mutation alone may give rise to trimethoprim resistance, additional mutations serve to enhance resistance and modulate the effects of existing mutations on the affinity of DHFR for its natural substrates.
In Vitro Growth of
Leishmania amazonensis
Promastigotes Resistant to Pentamidine Is Dependent on Interactions among Strains
Authors: Agnew P. , Holzmuller P. , Michalakis Y. , Sereno D. , Lemesre J. L. , Renaud F. 
Published: July 2002

ABSTRACT

The in vitro growth of promastigote cells of
Leishmania amazonensis
was found to strongly depend on interactions among strains that differed in their pentamidine resistance. In particular, the growth of resistant strains was reduced when they shared the same environment with a less-resistant strain.
Identification of
Proteus mirabilis
Mutants with Increased Sensitivity to Antimicrobial Peptides
Authors: McCoy Andrea J. , Liu Hongjian , Falla Timothy J. , Gunn John S. 
Published: July 2002

ABSTRACT

Antimicrobial peptides (APs) are important components of the innate defenses of animals, plants, and microorganisms. However, some bacterial pathogens are resistant to the action of APs. For example,
Proteus mirabilis
is highly resistant to the action of APs, such as polymyxin B (PM), protegrin, and the synthetic protegrin analog IB-367. To better understand this resistance, a transposon mutagenesis approach was used to generate
P. mirabilis
mutants sensitive to APs. Four unique PM-sensitive mutants of
P. mirabilis
were identified (these mutants were >2 to >128 times more sensitive than the wild type). Two of these mutants were also sensitive to IB-367 (16 and 128 times more sensitive than the wild type). Lipopolysaccharide (LPS) profiles of the PM- and protegrin-sensitive mutants demonstrated marked differences in both the lipid A and O-antigen regions, while the PM-sensitive mutants appeared to have alterations of either lipid A or O antigen. Matrix-assisted laser desorption ionization–time of flight mass spectrometry analysis of the wild-type and PM-sensitive mutant lipid A showed species with one or two aminoarabinose groups, while lipid A from the PM- and protegrin-sensitive mutants was devoid of aminoarabinose. When the mutants were streaked on an agar-containing medium, the swarming motility of the PM- and protegrin-sensitive mutants was completely inhibited and the swarming motility of the mutants sensitive to only PM was markedly decreased. DNA sequence analysis of the mutagenized loci revealed similarities to an
O
-acetyltransferase (PM and protegrin sensitive) and ATP synthase and
sap
loci (PM sensitive). These data further support the role of LPS modifications as an elaborate mechanism in the resistance of certain bacterial species to APs and suggest that LPS surface charge alterations may play a role in
P. mirabilis
swarming motility.
Mutation in the DNA Gyrase A Gene of
Escherichia coli
That Expands the Quinolone Resistance-Determining Region
Authors: Friedman S. Marvin , Lu Tao , Drlica Karl 
Published: July 2002

ABSTRACT

In three
Escherichia coli
mutants, a change (Ala-51 to Val) in the gyrase A protein outside the standard quinolone resistance-determining region (QRDR) lowered the level of quinolone susceptibility more than changes at amino acids 67, 82, 84, and 106 did. Revision of the QRDR to include amino acid 51 is indicated.
Mutant TEM β-Lactamase Producing Resistance to Ceftazidime, Ampicillins, and β-Lactamase Inhibitors
Authors: Vakulenko Sergei , Golemi Dasantila 
Published: July 2002

ABSTRACT

A derivative of the TEM-1 β-lactamase producing clinically significant levels of resistance to ceftazidime and β-lactamase inhibitors in the presence of penicillins was generated following five rounds of DNA shuffling and selection. This complex mutant enzyme contained three amino acid substitutions including those of residues 104 and 276 that are known to produce extended-spectrum resistance and, correspondingly, resistance to β-lactamase inhibitors. Although the Glu104Lys substitution by itself produced low levels of ceftazidime resistance, additional amino acid replacements in the enzyme with the triple mutation resulted in further enhancement of resistance to ceftazidime. Kinetic studies of the purified β-lactamase enzyme with the triple mutation indicated enhancement of the catalytic efficiency for turnover (
k
cat
/

K
m

) of ceftazidime. The increases in the

K
i

values of both clavulanic acid and tazobactam for the enzyme with the triple mutation were consistent with the observed bacterial resistance to the reversibility of β-lactam resistance with these inhibitors.
Pharmacokinetic Modeling and Simulations of Interaction of Amprenavir and Ritonavir
Authors: Sale Mark , Sadler Brian M. , Stein Daniel S. 
Published: July 2002

ABSTRACT

Data from three pharmacokinetic drug interaction studies of amprenavir and ritonavir were used to develop a pharmacokinetic interaction model using NONMEM (nonlinear mixed-effect model). A two-compartment linear model with first-order absorption best fit the amprenavir data, while a one-compartment model was used to describe the ritonavir data. The inhibition of elimination of amprenavir by ritonavir was modeled with a maximum effect (
E
max
) inhibition model and the observed ritonavir concentration. Monte Carlo simulation was then used to predict amprenavir concentrations for various combinations of amprenavir and ritonavir in twice-daily and once-daily dosing regimens. Simulated minimum amprenavir concentrations in plasma (
C
min
) in twice-daily and once-daily dosing regimens were compared with protein binding-adjusted 50% inhibitory concentrations (IC
50
s) for clinical human immunodeficiency virus isolates with different susceptibilities to protease inhibitors (central tendency ratios). The model based on the first two studies predicted the results of the third study. Data from all three studies were then combined to refine the final model. The observed and simulated noncompartmental pharmacokinetic parameters agreed well. From this model, several candidate drug regimens were simulated. These simulations suggest that, in patients who have clinically failed a traditional amprenavir regimen, a regimen of 600 mg of amprenavir with 100 mg of ritonavir twice daily would result in
C
min
-to-IC
50
ratios similar to that of 1,200 mg of amprenavir twice daily alone for wild-type viruses. In addition, once-daily regimens that result in
C
min
s above the protein binding-corrected IC
50
s for wild-type virus are clearly feasible.
Neurotoxic Mode of Action of Artemisinin
Authors: Schmuck Gabriele , Roehrdanz Elke , Haynes Richard K. , Kahl Regine 
Published: July 2002

ABSTRACT
We recently described a screening system designed to detect neurotoxicity of artemisinin derivatives based on primary neuronal brain stem cell cultures (G. Schmuck and R. K. Haynes, Neurotoxicity Res. 2:37-49, 2000). Here, we probe possible mechanisms of this brain stem-specific neurodegeneration, in which artemisinin-sensitive neuronal brain stem cell cultures are compared with nonsensitive cultures (cortical neurons, astrocytes). Effects on the cytoskeleton of brain stem cell cultures, but not that of cortical cell cultures, were visible after 7 days. However, after a recovery period of 7 days, this effect also became visible in cortical cells and more severe in brain stem cell cultures. Neurodegeneration appears to be induced by effects on intracellular targets such as the cytoskeleton, modulation of the energy status by mitochondrial or metabolic defects, oxidative stress or excitotoxic events. Artemisinin reduces intracellular ATP levels and the potential of the inner mitochondrial membrane below the cytotoxic concentration range in all three cell cultures, with these effects being most dominant in the brain stem cultures. Surprisingly, there were substantial effects on cortical neurons after 7 days and on astrocytes after 1 day. Artemisinin additionally induces oxidative stress, as observed as an increase of reactive oxygen species and of lipid peroxidation in both neuronal cell types. Interestingly, an induction of expression of AOE was only seen in astrocytes. Here, manganese superoxide dismutase (MnSOD) expression was increased more than 3-fold and catalase expression was increased more than 1.5-fold. In brain stem neurons, MnSOD expression was dose dependently decreased. Copper-zinc superoxide dismutase and glutathione peroxidase, two other antioxidant enzymes that were investigated, did not show any changes in their mRNA expression in all three cell types after exposure to artemisinin.
In Vitro Low-Level Resistance to Azoles in
Candida albicans
Is Associated with Changes in Membrane Lipid Fluidity and Asymmetry
Authors: Kohli Avmeet , Smriti NFN , Mukhopadhyay Kasturi , Rattan Ashok , Prasad Rajendra 
Published: July 2002

ABSTRACT

The present study tracks the development of low-level azole resistance in in vitro fluconazole-adapted strains of
Candida albicans
, which were obtained by serially passaging a fluconazole-susceptible dose-dependent strain, YO1-16 (fluconazole MIC, 16 μg ml
−1
) in increasing concentrations of fluconazole, resulting in strains YO1-32 (fluconazole MIC, 32 μg ml
−1
) and YO1-64 (MIC, 64 μg ml
−1
). We show that acquired resistance to fluconazole in this series of isolates is not a random process but is a gradually evolved complex phenomenon that involves multiple changes, which included the overexpression of ABC transporter genes, e.g.,
CDR1
and
CDR2
, and the azole target enzyme,
ERG11
. The sequential rise in fluconazole MICs in these isolates was also accompanied by cross-resistance to other azoles and terbinafine. Interestingly, fluorescent polarization measurements performed by using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene revealed that there was a gradual increase in membrane fluidity of adapted strains. The increase in fluidity was reflected by observed change in membrane order, which was considerably decreased (decrease in fluorescence polarization values,
P
value) in the adapted strain (
P
value of 0.1 in YO1-64, compared to 0.19 in the YO1-16 strain). The phospholipid composition of the adapted strain was not significantly altered; however, ergosterol content was reduced in YO1-64 from that in the YO1-16 strain. The asymmetrical distribution of phosphatidylethanolamine (PE) between two monolayers of plasma membrane was also changed, with PE becoming more exposed to the outer monolayer in the YO1-64 strain. The results of the present study suggest for the first time that changes in the status of membrane lipid phase and asymmetry could contribute to azole resistance in
C. albicans
.