bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multidrug Resistance of a Porin Deletion Mutant of
Mycobacterium smegmatis
Authors: Stephan Joachim , Mailaender Claudia , Etienne Gilles , Daffé Mamadou , Niederweis Michael 
Published: October 2004

ABSTRACT

Mycobacteria contain an outer membrane of unusually low permeability which contributes to their intrinsic resistance to many agents. It is assumed that small and hydrophilic antibiotics cross the outer membrane via porins, whereas hydrophobic antibiotics may diffuse through the membrane directly. A mutant of
Mycobacterium smegmatis
lacking the major porin MspA was used to examine the role of the porin pathway in antibiotic sensitivity. Deletion of the
mspA
gene caused high-level resistance of
M. smegmatis
to 256 μg of ampicillin/ml by increasing the MIC 16-fold. The permeation of cephaloridine in the
mspA
mutant was reduced ninefold, and the resistance increased eightfold. This established a clear relationship between the activity and the outer membrane permeation of cephaloridine. Surprisingly, the MICs of the large and/or hydrophobic antibiotics vancomycin, erythromycin, and rifampin for the
mspA
mutant were increased 2- to 10-fold. This is in contrast to those for
Escherichia coli
, whose sensitivity to these agents was not affected by deletion of porin genes. Uptake of the very hydrophobic steroid chenodeoxycholate by the
mspA
mutant was retarded threefold, which supports the hypothesis that loss of MspA indirectly reduces the permeability by the lipid pathway. The multidrug resistance of the
mspA
mutant highlights the prominent role of outer membrane permeability for the sensitivity of
M. smegmatis
to antibiotics. An understanding of the pathways across the outer membrane is essential to the successful design of chemotherapeutic agents with activities against mycobacteria.
Inhibition of Antibiotic Efflux in Bacteria by the Novel Multidrug Resistance Inhibitors Biricodar (VX-710) and Timcodar (VX-853)
Authors: Mullin Steve , Mani Nagraj , Grossman Trudy H. 
Published: October 2004

ABSTRACT

Inhibitors of mammalian multidrug efflux, such as the plant alkaloid reserpine, are also active in potentiating antibiotic activity by inhibiting bacterial efflux. Based on this precedent, two novel mammalian multiple drug resistance inhibitors, biricodar (VX-710) and timcodar (VX-853), were evaluated for activity in a variety of bacteria. Both VX-710 and VX-853 potentiated the activity of ethidium bromide (EtBr), a model efflux substrate, against three clinically significant gram-positive pathogens:
Staphylococcus aureus
,
Enterococcus faecalis
, and
Streptococcus pneumoniae
. Similar to reserpine, VX-710 and VX-853 directly blocked EtBr efflux in
S. aureus
. Furthermore, these compounds were effective in lowering the MICs of several clinically used antibiotics, including fluoroquinolones, suggesting that VX-710 and VX-853 are representatives of a new class of bacterial efflux inhibitors with the potential for use in combination therapy.
Promoter Sequences Necessary for High-Level Expression of the Plasmid-AssociatedampCβ-Lactamase GeneblaMIR-1
Authors: Reisbig Mark D. , Hanson Nancy D. 
Published: October 2004

ABSTRACTLittle is known about mechanisms involved in high-level expression of plasmid-associatedampCgenes. The sequence forblaMIR-1has been elucidated, and the gene is not inducible. Although the sequence for the promoter (prA) that drives expression ofEnterobacter cloacaechromosomalampCis present upstream ofblaMIR-1, high-level expression fromblaMIR-1is directed from a hybrid promoter (prB) located further upstream of prA. The purpose of this study was to determine the influence of each promoter onblaMIR-1expression and β-lactam resistance. RNA expression by deletion clones with both promoters was measured and compared to that by clones in which −35 and/or −10 elements of prA and/or prB were altered. Primer extension revealed two start sites forblaMIR-1transcription. Expression ofblaMIR-1in clones with both promoters was 171-fold higher than that in clones carrying only prA. In addition,blaMIR-1expression from prA increased 11-fold in the presence of the prB −10 element compared to expression driven from prA alone. Ceftazidime and cefotaxime MICs increased 42- and 64-fold, respectively, for the clone expressingblaMIR-1from both promoters compared to expression from prA alone. The upstream promoter prB ofblaMIR-1is solely responsible for high-level expression required for cefotaxime and ceftazidime resistance. These data suggest that resistance to extended-spectrum cephalosporins mediated by noninducible plasmid-associatedampCgenes requires the formation of novel promoter elements that are capable of increasingampCexpression.
Emergence and Persistence of Macrolide Resistance in Oropharyngeal Flora and Elimination of Nasal Carriage of
Staphylococcus aureus
after Therapy with Slow-Release Clarithromycin: a Randomized, Double-Blind, Placebo-Controlled Study
Authors: Berg Hans F. , Tjhie Jeroen H. T. , Scheffer Gert-Jan , Peeters Marcel F. , van Keulen Peter H. J. , Kluytmans Jan A. J. W. , Stobberingh Ellen E. 
Published: October 2004

ABSTRACT

To investigate the effect of slow-release (SR) clarithromycin on colonization and the development of resistance in oropharyngeal and nasal flora, a double-blind, randomized, placebo-controlled trial was performed with 8 weeks of follow-up. A total of 296 patients with documented coronary artery disease were randomized in the preoperative outpatient clinic to receive a daily dose of SR clarithromycin (500 mg) (CL group) or placebo tablets (PB group) until the day of surgery. Nose and throat swabs were taken before the start of therapy, directly after the end of therapy, and 8 weeks later. The presence of potential pathogenic bacteria was determined, and if they were isolated, MIC testing was performed. Quantitative culture on media with and without macrolides was performed for the indigenous oropharyngeal flora. In addition, analysis of the mechanism of resistance was performed with the macrolide-resistant indigenous flora. Basic patient characteristics were comparable in the two treatment groups. The average number of tablets taken was 15 (standard deviation = 6.4). From the throat swabs,
Haemophilus parainfluenzae
was isolated and carriage was not affected in either of the treatment groups. Nasal carriage of
Staphylococcus aureus
, however, was significantly reduced in the CL group (from 35.3 to 4.3%) compared to the PB group (from 32.4 to 30.3%) (
P
< 0.0001; relative risk [RR], 7.0; 95% confidence interval [CI], 3.1 to 16.0). Resistance to clarithromycin was present significantly more frequently in
H. parainfluenzae
in the CL group after treatment (
P
= 0.007; RR, 1.6; 95% CI, 1.1 to 2.3); also, the percentage of patients with resistance to macrolides in the indigenous flora after treatment was significantly higher in the CL group (31 to 69%) (
P
< 0.0001; RR, 1.9; 95% CI, 1.4 to 2.5). This persisted for at least 8 weeks. This study shows that besides the effective elimination of nasal carriage of
S. aureus
, treatment with SR clarithromycin for approximately 2 weeks has a marked and sustained effect on the development of resistance in the oropharyngeal flora for at least 8 weeks.
Differential Maintenance of the M184V Substitution in the Reverse Transcriptase of Human Immunodeficiency Virus Type 1 by Various Nucleoside Antiretroviral Agents in Tissue Culture
Authors: Petrella Marco , Oliveira Maureen , Moisi Daniela , Detorio Mervi , Brenner Bluma G. , Wainberg Mark A. 
Published: October 2004

ABSTRACTThe M184V substitution in human immunodeficiency virus type 1 reverse transcriptase (RT) is rapidly selected in tissue culture following serial passage of wild-type virus in the presence of increasing concentrations of lamivudine (3TC). M184V is also associated with several alterations of RT enzymatic function in vitro that may adversely affect viral fitness or replication capacity, which creates a potential rationale for its maintenance once it has been selected by antiviral chemotherapy. However, the relative effectiveness of nucleoside RT inhibitors that are structurally unrelated to 3TC in selecting and/or maintaining M184V has not been investigated. In the present study, we have studied the abilities of a variety of drugs, i.e., zalcitabine (ddC), didanosine (ddI), abacavir (ABC), and the novel nucleoside SPD754, in addition to 3TC, to maintain the presence of M184V in tissue culture and have shown that SPD754, ABC, and 3TC are able to preserve M184V in mixed dual infections consisting of wild-type viruses and clinical isolates which contained the M184V mutation. Moreover, M184V could also be maintained in these cultures when a subtherapeutic concentration of 3TC (i.e., 0.05 μM) was used. In contrast, neither ddI nor ddC was able to maintain M184V to the same extent as the other drugs after 10 weeks of tissue culture in mixtures of wild-type viruses and isolates containing M184V in different proportions.
Pharmacodynamics of Pulse Dosing versus Standard Dosing: In Vitro Metronidazole Activity against
Bacteroides fragilis
and
Bacteroides thetaiotaomicron
Authors: Ibrahim Khalid H. , Gunderson Brent W. , Hermsen Elizabeth D. , Hovde Laurie B. , Rotschafer John C. 
Published: October 2004

ABSTRACT

Pulse dosing is a novel approach to dosing that produces escalating antibiotic levels early in the dosing interval followed by a prolonged dose-free period. Antibiotic is frontloaded by means of four sequential bolus injections, after which antibiotic levels are allowed to diminish until the next dose. This study compares standard thrice-daily dosing and pulse dosing of metronidazole against
Bacteroides
spp. in an in vitro model. Two American Type Culture Collection
Bacteroides fragilis
isolates (metronidazole MIC for each organism = 1 mg/liter) were exposed to metronidazole for 48 or 96 h. Human pharmacokinetics were simulated for an oral 500-mg dose given every 8 h (maximum concentration of drug [
C
max
] = 12 mg/liter; half-life = 8 h; area under the curve [AUC] = 294 mg · h/liter) and for pulse dosing. Pulses, each producing an increase in metronidazole concentration of 9 mg/liter, were administered at times 0, 2, 4, and 6 h of each 24-h cycle, with a targeted half-life of 8 h (AUC = 347 mg · h/liter). A metronidazole-resistant
B. fragilis
strain (metronidazole MIC = 32 mg/liter) was exposed to both dosing regimens and, additionally, to a regimen of 1,500 mg administered once daily (
C
max
= 36 mg/liter; AUC = 364 mg · h/liter). Furthermore, regimens against one
B. fragilis
isolate and one
B. thetaiotaomicron
isolate corresponding to one-fourth and one-eighth of the thrice-daily and pulse dosing regimens, mimicking peak metronidazole concentrations achieved in abscesses, were simulated in 48-h experiments (metronidazole MIC = 1 mg/liter). Time-kill curves were generated for each experiment and analyzed for bactericidal activity, defined as a bacterial burden reduction ≥ 3 log
10
CFU/ml. The results of paired (Wilcoxon matched-pair signed-rank test) and nonpaired (Mann-Whitney test) statistical analyses conducted on time to 3 log
10
kill data and area under the kill curve data from each of the thrice-daily dosing experiments versus each of the pulse dosing experiments were considered not significant for a given isolate-dosing regimen combination. The thrice-daily dosing, pulse dosing, and once-daily dosing regimens all exhibited bactericidal activity. Metronidazole administered in standard or pulse dosing fashion was highly active against both susceptible and resistant strains of
Bacteroides
spp.
Pharmacokinetics of Indinavir and Ritonavir Administered at 667 and 100 Milligrams, Respectively, Every 12 Hours Compared with Indinavir Administered at 800 Milligrams Every 8 Hours in Human Immunodeficiency Virus-Infected Patients
Authors: Rhame Frank S. , Rawlins Sandy L. , Petruschke Richard A. , Erb Tara A. , Winchell Gregory A. , Wilson Helene M. , Edelman Jonathan M. , Abramson Murray A. 
Published: October 2004

ABSTRACT

Human immunodeficiency virus (HIV) patients on nucleoside or nucleotide reverse transcriptase inhibitors with HIV RNA at <1,000 copies/ml were randomized in an open-label study to administration of combined indinavir/ritonavir (IDV/RTV) at 667/100 mg every 12 h (q12h) or IDV alone at 800 mg q8h to determine the regimens' pharmacokinetics. On day 14, plasma IDV and RTV levels were determined over 24 h. Noncompartmental pharmacokinetics (minimum concentration of drug in serum [
C
min
], area under the concentration-time curve from 0 to 24 h [AUC
0-24
], and maximum concentration of drug in serum [
C
max
]) were expressed as geometric mean values with 90% confidence intervals (CI). The primary hypothesis was that the lower bound of the protocol-specified 90% CI for the geometric mean
C
min
ratio of the combination compared to IDV alone regimen would be ≥2. Twenty-seven patients were enrolled, and 24 (15 male; average age, 42 years) completed the study. The
C
min
, AUC
0-24
, and
C
max
for IDV/RTV compared to IDV alone were 1,511 versus 250 nM, 119,557 versus 77,034 nM · h, and 10,428 versus 10,407 nM, respectively. Corresponding relationships for IDV/RTV compared to IDV alone were a 6.0-fold increase in
C
min
(90% CI, 4.0, 9.3), an increase in AUC
0-24
(1.5-fold, 90% CI, 1.2, 2.0), and no increase in
C
max
. Adverse events were similar and generally mild, with no cases of nephrolithiasis. The geometric mean ratio of IDV
C
min
for IDV/RTV compared to IDV was at least 2 by a lower bound of the 90% CI, satisfying the primary hypothesis. The
C
max
was not increased, suggesting an IDV/RTV 667/100-mg toxicity profile may be similar to that of unboosted IDV.
Highly Active Anti-
Pneumocystis carinii
Compounds in a Library of Novel Piperazine-Linked Bisbenzamidines and Related Compounds
Authors: Cushion Melanie T. , Walzer Peter D. , Collins Margaret S. , Rebholz Sandra , Vanden Eynde Jean Jacques , Mayence Annie , Huang Tien L. 
Published: October 2004

ABSTRACT

Trimethoprim-sulfamethoxazole and pentamidine isethionate have been used extensively for the prophylaxis and therapy of pneumonia caused by
Pneumocystis jirovecii
. Problems associated with toxicity and potential emerging resistance for both therapies necessitate the development of safe and effective analogs or new treatment strategies. In the present study, a library of 36 compounds was synthesized by using the pentamidine molecule as the parent compound modified by a 1,4-piperazinediyl moiety as the central linker to restrict conformation flexibility. The compounds were evaluated for anti-
Pneumocystis carinii
activity in a bioluminescent ATP-driven assay. Four of the compounds were highly active, with 50% inhibitory concentration (IC
50
) values of <0.01 μg/ml; four had very marked activity (IC
50
< 0.10 μg/ml); ten had marked activity (IC
50
< 1.0 μg/ml); nine had moderate activity (IC
50
< 10 μg/ml); one had slight activity (IC
50
= 34.1 μg/ml); and the remaining eight did not demonstrate activity in this assay system. The high level of activity was specifically associated with an alkyl chain length of five to six carbons attached to one of the nitrogens of the bisamidinium groups. None of the highly active compounds and only one of the very marked compounds exhibited any toxicity when evaluated in three mammalian cell lines. The strategy of substitution of 1,4-piperazine-linked bisbenzamidines produced compounds with the highest level of activity observed in the ATP assay and holds great promise for the development of efficacious anti-
P. carinii
therapy.
Comparative Pharmacokinetics of Intramuscular Artesunate and Artemether in Patients with Severe Falciparum Malaria
Authors: Hien T. T. , Davis T. M. E. , Chuong L. V. , Ilett K. F. , Sinh D. X. T. , Phu N. H. , Agus C. , Chiswell G. M. , White N. J. , Farrar J. 
Published: October 2004

ABSTRACT

The first-dose pharmacokinetic properties of intramuscular (i.m.) artesunate (ARTS; 2.4 mg/kg immediately [stat], followed by 1.2 mg/kg i.m. daily) and artemether (ARM; 3.2 mg/kg i.m. stat, followed by 1.6 mg/kg i.m. daily) were compared in Vietnamese adults with severe falciparum malaria. A total of 19 patients were studied; 9 received ARTS, and 10 received ARM. ARTS was absorbed very rapidly; concentrations in plasma peaked between 1,362 and 8,388 nmol/liter (median, 5,710 nmol/liter) within 20 min of injection and then declined with a median (range) half-life (
t
1/2
) of 30 (3 to 67) min. ARTS was hydrolyzed rapidly and completely to the biologically active metabolite dihydroartemisinin (DHA). Peak DHA concentrations in plasma ranged between 1,718 and 7,080 nmol/liter (median, 3,060 nmol/liter) and declined with a
t
1/2
of 52 (26 to 69) min. In contrast, ARM was slowly and erratically absorbed. The absorption profile appeared biphasic. Maximum ARM concentrations in plasma ranged between 67 nmol/liter (a value close to the 50% inhibitory concentration for some
Plasmodium falciparum
isolates) and 1,631 nmol/liter (median, 574 nmol/liter) and occurred at a median (range) of 10 (1.5 to 24) h. There was relatively little conversion to DHA. After i.m. injection in cases of severe malaria, absorption of the water-soluble ARTS is rapid and extensive, whereas the oil-based ARM is slowly and erratically absorbed, with relatively little conversion to the more active DHA. On the basis of this pharmacological study, parenteral ARTS is preferable to ARM as an initial antimalarial therapy, particularly in the most seriously ill patients. These findings should be formally assessed by a randomized clinical trial.
Concentrations of Gemifloxacin at the Target Site in Healthy Volunteers after a Single Oral Dose
Authors: Islinger Florian , Bouw Rene , Stahl Mathias , Lackner Edith , Zeleny Petra , Brunner Martin , Müller Markus , Eichler Hans Georg , Joukhadar Christian 
Published: October 2004

ABSTRACT

Free gemifloxacin concentrations in the interstitial space fluid of skeletal muscle and subcutaneous adipose tissue were measured by means of in vivo microdialysis to characterize the ability of gemifloxacin to penetrate human soft tissues. Twelve healthy volunteers received a single oral dose of 320 mg of gemifloxacin. The mean areas under the concentration-time curves from 0 to 10 h (AUC
0-10
) were significantly higher for soft tissue than for unbound gemifloxacin in plasma (
P
< 0.05). The ratios of the mean AUC
0-10
for tissue to the AUC
0-10
for free gemifloxacin in plasma were 1.7 ± 0.7 (mean ± standard deviation) for skeletal muscle and 2.4 ± 1.0 for adipose tissue. The AUC
0-24
ratios for free gemifloxacin in tissues to the MIC at which 90% of frequently isolated bacteria are inhibited were close to or higher than 100 h. Therefore, based on pharmacokinetic and pharmacodynamic calculations, we conclude that gemifloxacin might be a useful therapeutic option for the treatment of soft tissue infections.
Complex Multiple Antibiotic and Mercury Resistance Region Derived from the r-det of NR1 (R100)
Authors: Partridge Sally R. , Hall Ruth M. 
Published: October 2004

ABSTRACT

The sequence of the 45.2-kb multidrug and mercury resistance region of pRMH760, a large plasmid from a clinical isolate of
Klebsiella pneumoniae
collected in 1997 in Australia, was completed. Most of the modules found in the resistance determinant (r-det), or Tn
2670
, region of NR1 (also known as R100), isolated from a
Shigella flexneri
strain in Japan in the late 1950s, were present in pRMH760 but in a different configuration. The location was also different, with the Tn
2670
-derived region flanked by the transposition module of Tn
1696
and a mercury resistance module almost identical to one found in the plasmid pDU1358. This arrangement is consistent with a three-step process. First, the r-det was circularized via homologous recombination between the IS
1
elements and reincorporated at a new location, possibly in a different plasmid, via homologous recombination between the 5′-conserved (5′-CS) or 3′-CS of the In34 integron in the r-det and the same region of a second class 1 integron in a Tn
1696
relative. Subsequently, resolvase-mediated recombination between the
res
sites in the r-det and a second mercury resistance transposon removed one end of the Tn
1696
-like transposon and part of the second transposon. Other events occurring within the r-det-derived portion have also contributed to the formation of the pRMH760 resistance region. Tn
2
or a close relative that includes the
bla
TEM-1b
gene had moved into the Tn
21
mercury resistance module with subsequent deletion of the adjacent sequence, and all four 38-bp inverted repeats corresponding to Tn
21
family transposon termini have been interrupted by an IS
4321
-like element.
Steady-State Pharmacokinetics of a Double-Boosting Regimen of Saquinavir Soft Gel plus Lopinavir plus Minidose Ritonavir in Human Immunodeficiency Virus-Infected Adults
Authors: Ribera Esteban , Lopez Rosa M. , Diaz Marjorie , Pou Leonor , Ruiz Lidia , Falcó Vicenç , Crespo Manuel , Azuaje Carlos , Ruiz Isabel , Ocaña Imma , Clotet Bonaventura , Pahissa Albert 
Published: October 2004

ABSTRACT

Management of treatment-experienced human immunodeficiency virus patients has become complex, and therapy may need to include two protease inhibitors at therapeutic doses. The objective of this study was to characterize the pharmacokinetics in serum of saquinavir (1,000 mg twice daily [b.i.d.]), lopinavir (400 mg b.i.d.), and ritonavir (100 mg b.i.d.) in a multidrug rescue therapy study and to investigate whether steady-state pharmacokinetics of lopinavir-ritonavir are affected by coadministration of saquinavir. Forty patients were included (25 given ritonavir, lopinavir, and saquinavir and 15 given ritonavir and lopinavir). The median pharmacokinetic parameters of lopinavir were as follows: area under the concentration-time curve from 0 to 12 h (AUC
0-12
), 85.1 μg/ml · h; maximum concentration of drug in serum (
C
max
), 10.0 μg/ml; trough concentration of drug in serum (
C
trough
), 7.3 μg/ml; and minimum concentration of drug in serum (
C
min
), 5.5 μg/ml. Lopinavir concentrations were similar in patients with and without saquinavir. The median pharmacokinetic parameters for saquinavir were as follows: AUC
0-12
, 22.9 μg/ml · h;
C
max
, 2.9 μg/ml;
C
trough
, 1.6 μg/ml; and
C
min
, 1.4 μg/ml. There was a strong linear correlation between lopinavir and ritonavir and between saquinavir and ritonavir concentrations in plasma. The correlation between lopinavir and saquinavir levels was weaker. We found higher saquinavir concentrations in women than in men, with no difference in lopinavir levels. Only patients with very high body weight presented lopinavir and saquinavir concentrations lower than the overall group. Ritonavir has a double-boosting function for both lopinavir and saquinavir, and in terms of pharmacokinetics, the drug doses selected seemed appropriate for combining these agents in a dual protease inhibitor-based antiretroviral regimen for patients with several prior virologic failures.