bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antibiotic-Induced Lipopolysaccharide (LPS) Release fromSalmonella typhi: Delay between Killing by Ceftazidime and Imipenem and Release of LPS
Authors: van Langevelde Petra , Kwappenberg Kitty M. C. , Groeneveld Paul H. P. , Mattie Herman , van Dissel Jaap T. 
Published: October 2018

ABSTRACTIt has been suggested that the antibiotic-induced release of lipopolysaccharide (LPS) is an important cause of the development of septic shock in patients treated for severe infections caused by gram-negative bacteria. β-Lactam antibiotics change the integrity of the bacterial cell envelope by binding to penicillin-binding proteins (PBP) in the membrane and thus may affect the amount of LPS that is released and the kinetics of that release. In this respect, ceftazidime at intermediate concentrations binds with a high affinity to PBP 3 and PBP 1a and thus can induce filament formation in addition to killing, whereas imipenem preferentially binds to PBP 2 and PBP 1b, leading to spheroplast formation and rapid cell lysis. We investigated the effects of these antibiotics on the killing and the release of the radioactively labelled LPS ofSalmonella typhiTy 21A. A mathematical model was developed to calculate the delay between bacterial killing and LPS release, designated the lag time. At antibiotic concentrations inducing equal killing, the amount of LPS released was the same for both antibiotics. Only after 6 h of incubation at antibiotic concentrations above 0.5 μg/ml, the amount of3H-LPS released was slightly higher (∼1.2-fold) in incubations with ceftazidime than in those with imipenem, and the maximum releases of the total label were 33.2% ± 0.89% and 27.1% ± 0.45%, respectively. Despite the clear concentration-dependent effect on the bacterial killing and subsequent LPS release, the lag time was independent of the antibiotic concentration. For ceftazidime as well as imipenem the lag time amounted to approximately 60 min. In conclusion, our findings imply that the mechanism of antibiotic-induced LPS release is independent of the PBP affinities for these β-lactam antibiotics. Furthermore, once the organism is killed by either imipenem or ceftazidime, the rate of LPS release fromS. typhidoes not differ according to the antibiotic with which the organism is killed, and there is little difference in the relative amount of LPS released.
Use of Pharmacodynamic Parameters To Predict Efficacy of Combination Therapy by Using Fractional Inhibitory Concentration Kinetics
Authors: den Hollander Jan G. , Mouton Johan W. , Verbrugh Henri A. 
Published: October 2018

ABSTRACT

Combination therapy with antimicrobial agents can be used against bacteria that have reduced susceptibilities to single agents. We studied various tobramycin and ceftazidime dosing regimens against four resistant
Pseudomonas aeruginosa
strains in an in vitro pharmacokinetic model to determine the usability of combination therapy for the treatment of infections due to resistant bacterial strains. For the selection of an optimal dosing regimen it is necessary to determine which pharmacodynamic parameter best predicts efficacy during combination therapy and to find a simple method for susceptibility testing. An easy-to-use, previously described E-test method was evaluated as a test for susceptibility to combination therapy. That test resulted in a MIC
combi
, which is the MIC of, for example, tobramycin in the presence of ceftazidime. By dividing the tobramycin and ceftazidime concentration by the MIC
combi
at each time point during the dosing interval, fractional inhibitory concentration (FIC) curves were constructed, and from these curves new pharmacodynamic parameters for combination therapy were calculated (i.e., AUC
combi
,
C
max-combi
,
T
>MIC-combi
, and
T
>FICi
, where AUC
combi
,
C
max-combi
,
T
>MIC-combi
, and
T
>FICi
are the area under the FIC
combi
curve, the peak concentration of FIC
combi
, the time that the concentration of the combination is above the MIC
combi
, and the time above the FIC index, respectively). By stepwise multilinear regression analysis, the pharmacodynamic parameter
T
>FICi
proved to be the best predictor of therapeutic efficacy during combination therapy with tobramycin and ceftazidime (
R
2
= 0.6821;
P
< 0.01). We conclude that for combination therapy with tobramycin and ceftazidime the
T
>FICi
is the parameter best predictive of efficacy and that the E-test for susceptibility testing of combination therapy gives promising results. These new pharmacodynamic parameters for combination therapy promise to provide better insight into the rationale behind combination therapy.
Imiquimod, a Patient-Applied Immune-Response Modifier for Treatment of External Genital Warts
Authors: Beutner Karl R. , Tyring Stephen K. , Trofatter Kenneth F. , Douglas John M. , Spruance Spotswood , Owens Mary L. , Fox Terry L. , Hougham Andrina J. , Schmitt Kathy A. 
Published: October 2018

ABSTRACTGenital human papillomavirus infection is one of the most common sexually transmitted diseases. Imiquimod is a new agent, an immune-response modifier, that has been demonstrated to have potent in vivo antiviral and antitumor effects in animal models. The present prospective, multicenter, double-blind, randomized, vehicle-controlled trial evaluated the efficacy and safety of daily patient-applied imiquimod for up to 16 weeks for the treatment of external genital warts. Wart recurrence was investigated during a 12-week treatment-free follow-up period. In the intent-to-treat analysis, baseline warts cleared from 49 of 94 (52%) patients treated with 5% imiquimod cream, 13 of 90 (14%) patients treated with 1% imiquimod cream, and 3 of 95 (4%) vehicle-treated patients; the differences between the groups treated with vehicle and imiquimod were significant (P< 0.0001). For subjects who completed the follow-up period, recurrence rates after a complete response were 19% (9 of 48 patients) in the 5% imiquimod cream group, 17% (2 of 12) in the 1% imiquimod cream group, and 0% (0 of 3) in the vehicle-treated group. There were no systemic reactions, although local skin reactions (generally of mild or moderate severity) were common, particularly in the 5% imiquimod cream group. Local reactions caused two patients to discontinue treatment. The most frequently reported local skin reactions were erythema, excoriation or flaking, and erosion. Patient-applied 5% imiquimod cream is effective for the treatment of external genital warts and has a favorable safety profile.
Accumulation of Norfloxacin by
Mycobacterium aurum
and
Mycobacterium smegmatis
Authors: Williams Kerstin J. , Chung Gavin A. C. , Piddock Laura J. V. 
Published: October 2018

ABSTRACT

The modified fluorescence method was used to determine the accumulation of norfloxacin by
Mycobacterium aurum
A+ and
Mycobacterium smegmatis
mc
2
155. By using an exogenous norfloxacin concentration of 10 μg/ml, a steady-state concentration (SSC) of 160 to 180 ng of norfloxacin/mg of cells was obtained for
M. aurum
, and an SSC of 120 to 140 ng of norfloxacin/mg of cells obtained for
M. smegmatis
. For both species of mycobacteria, the SSC was achieved within 5 min. The silicon oil method was investigated and gave higher SSCs than the modified fluorescence method. Further studies on the mechanism of norfloxacin accumulation by
M. aurum
were performed. An increase in the pH of the wash buffer from 7.0 to 9.0 did not significantly affect the final SSC obtained. Accumulation was nonsaturated over a norfloxacin concentration range of 0 to 100 μg/ml, and the proton motive force inhibitor 2,4-dinitrophenol (1 and 2 mM), whether it was added before or after norfloxacin was added, had no effect on the final SSC obtained. 2,4-Dinitrophenol also had no effect on norfloxacin accumulation by
M. smegmatis
. Furthermore, norfloxacin accumulation by
M. aurum
was unaffected by the presence of either Tween 80 or subinhibitory concentrations of ethambutol in the growth medium. Therefore, it is proposed that norfloxacin accumulation by mycobacteria occurs by simple, energy-independent diffusion.
Generation and Characterization of a Mutant of Influenza A Virus Selected with the Neuraminidase Inhibitor BCX-140
Authors: Bantia Shanta , Ghate Anita A. , Ananth Sandya L. , Babu Y. Sudhakar , Air Gillian M. , Walsh Gerald M. 
Published: October 2018

ABSTRACT

Influenza neuraminidase (NA) plays an important role in viral replication, and characterization of viruses resistant to NA inhibitors will help elucidate the role of active-site residues. This information will assist in designing better inhibitors targeted to essential active-site residues that cannot generate drug-resistant mutations. In the present study we used the benzoic acid-based inhibitor BCX-140 to select and characterize resistant viruses. BCX-140 binds to the NA active site in an orientation that is opposite that of a sialic acid-based compound, 4-guanidino-2,4-dideoxy-2,3-dehydro-
N
-acetylneuraminic acid (GANA). Thus, the guanidino group of BCX-140 binds to Glu-276, whereas in GANA the guanidino group binds to Glu-119. We passaged influenza A/Singapore/1/57 (H2N2) in Madin-Darby canine kidney cells in the presence of BCX-140, and virus resistant to this inhibitor was selected after six passages. The NA of this mutant was still sensitive to inhibition by BCX-140. However, the mutant virus was resistant to BCX-140 in plaque and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Sequence analysis of hemagglutinin (HA) and NA genes revealed changes in both, although none were in the active site of the NA. Depending on the method of selection of the resistant virus, two types of changes associated with the sialic acid binding site were seen in the HA. One is a change in HA1 of Ala-133 to Thr, a residue close to the binding site, while the other change was Arg-132 of HA1 to Gln, which in HA1 of serotype H3 is a sialic acid contact (Asn-137). Binding studies revealed that both types of resistant viruses had reduced receptor binding affinity compared to that of the wild type. Thus, resistance to BCX-140 was generated by modifying the HA. NA active-site residue 276 may be essential for activity, and thus, it cannot be changed to generate resistance. However, drug-induced changes in the HA can result in a virus that is less dependent on NA activity for growth in cells and, hence, resistant to NA inhibitors.
In Vitro Activity of a New 8-Methoxyquinolone, BAY 12-8039, against
Chlamydia pneumoniae
Authors: Roblin Patricia M. , Hammerschlag Margaret R. 
Published: October 2018

ABSTRACT

The in vitro susceptibilities of 10 strains of
Chlamydia pneumoniae
to a new 8-methoxyquinolone, BAY 12-8039, and to ofloxacin, doxycycline, and erythromycin were determined. The activity of BAY 12-8039 was similar to that of ofloxacin, with a MIC at which 90% of the isolates had no inclusions and a minimal chlamydicidal concentration at which 90% of the isolates had no inclusions after passage of 1.0 μg/ml, but this activity was less than those of doxycycline and erythromycin.
In Vitro Activity of Levofloxacin against a Selected Group of Anaerobic Bacteria Isolated from Skin and Soft Tissue Infections
Authors: Wexler Hannah M. , Molitoris Eric , Molitoris Denise , Finegold Sydney M. 
Published: October 2018

ABSTRACT

The in vitro activity of levofloxacin was compared to the activities of ofloxacin, ciprofloxacin, ampicillin-sulbactam (2:1), cefoxitin, and metronidazole for a selected group of anaerobes (
n
= 175) isolated from skin and soft tissue infections by using the National Committee for Clinical Laboratory Standards-approved Wadsworth method. Ampicillin-sulbactam and cefoxitin inhibited 99% of the strains of this select group, levofloxacin and ofloxacin inhibited 73 and 50%, respectively, at 2 μg/ml, and ciprofloxacin inhibited 51% at 1 μg/ml. The geometric mean MIC of levofloxacin was lower than those of ofloxacin and ciprofloxacin for every group except
Veillonella.
Characteristics and Dynamics of Bacterial Populations during Postantibiotic Effect Determined by Flow Cytometry
Authors: Gottfredsson Magnús , Erlendsdóttir Helga , Sigfússon Ásbjörn , Gudmundsson Sigurdur 
Published: October 2018

ABSTRACT

Changes in bacterial ultrastructure after antibiotic exposure and during the postantibiotic effect (PAE) have been demonstrated by electron microscopy (EM). However, EM is qualitative and subject to individual interpretation. In contrast, flow cytometry gives qualitative and quantitative information. The sizes and nucleic acid contents of
Escherichia coli
and
Pseudomonas aeruginosa
were studied during antimicrobial exposure as well as during the PAE period by staining the organisms with propidium iodide and analyzing them with flow cytometry and fluorescence microscopy. The effects of ampicillin, ceftriaxone, ciprofloxacin, gentamicin, and rifampin were studied for
E. coli
, whereas for
P. aeruginosa
imipenem and ciprofloxacin were investigated. After exposure of
E. coli
to ampicillin, ceftriaxone, and ciprofloxacin, filamentous organisms were observed by fluorescence microscopy. These changes in morphology were reflected by increased forward light scatter (FSC) and nucleic acid content as measured by flow cytometry. For the β-lactams the extent of filamentation increased in a dose-dependent manner after drug removal, resulting in formation of distinct subpopulations of bacteria. These changes peaked at 20 to 35 min, and bacteria returned to normal after 90 min after drug removal. In contrast, the subpopulations induced by ciprofloxacin did not return to normal until >180 min after the end of the classically defined PAE. Rifampin resulted in formation of small organisms with low FSC, whereas no distinctive characteristics were noted after gentamicin exposure. For
P. aeruginosa
an identifiable subpopulation of large globoid cells and increased nucleic acid content was detected after exposure to imipenem. These changes persisted past the PAE, as defined by viability counting. Swollen organisms with increased FSC were detected after ciprofloxacin exposure, even persisting during bacterial growth. In summary, for β-lactam antibiotics and ciprofloxacin, the PAE is characterized by dynamic formation of enlarged cell populations of increased nucleic acid content, whereas rifampin induces a decrease in size and nucleic acid content in the organisms. Flow cytometry is an ideal method for future studies of bacterial phenotypic characteristics during the PAE.
Isolation of Nitrofurantoin-Resistant Mutants of Nitroreductase-Producing
Clostridium
sp. Strains from the Human Intestinal Tract
Authors: Rafii Fatemeh , Hansen Eugene B. 
Published: October 2018

ABSTRACT

Five spontaneous nitrofurantoin-resistant mutants (one each of
Clostridium leptum
,
Clostridium paraputrificum
, two other
Clostridium
spp. strains from the human intestinal microflora, and
Clostridium perfringens
ATCC 3626) were selected by growth on a nitrofurantoin-containing medium. All of the
Clostridium
wild-type and mutant strains produced nitroreductase, as was shown by the conversion of 4-nitrobenzoic acid to 4-aminobenzoic acid. High-performance liquid chromatography (HPLC) analysis of the mutants during incubation with 50 μg of nitrofurantoin per ml showed the gradual disappearance of the nitrofurantoin peak. The nitrofurantoin peak also disappeared when cell-free supernatants instead of cultures of each of the resistant and wild-type bacteria were used, but it persisted if the cell-free supernatants had been inactivated by heat. At least two of the mutants converted nitrofurantoin to metabolites without antibacterial activity, as was shown by a bioassay with a nitrofurantoin-susceptible
Bacillus
sp. strain. Nitrofurantoin at a high concentration (50 μg/ml) continued to exert some toxicity, even on the resistant strains, as was evident from the longer lag phases. This study indicates that
Clostridium
strains can develop resistance to nitrofurantoin while retaining the ability to produce nitroreductase; the mutants metabolized nitrofurantoin to compounds without antibacterial activity.
Steady-State Pharmacokinetics and Electrocardiographic Pharmacodynamics of Clarithromycin and Loratadine after Individual or Concomitant Administration
Authors: Carr Robert A. , Edmonds Anthony , Shi Harry , Locke Charles S. , Gustavson Linda E. , Craft J. Carl , Harris Stuart I. , Palmer Robert 
Published: October 2018

ABSTRACT

To evaluate the potential for an interaction between clarithromycin and loratadine, healthy male volunteers (
n
= 24) received each of the following regimens according to a randomized crossover design: 500 mg of clarithromycin orally every 12 h (q12h) for 10 days, 10 mg of loratadine orally q24h for 10 days, and the combination of clarithromycin and loratadine. A washout interval of 14 days separated regimens. The addition of loratadine did not statistically significantly affect the steady-state pharmacokinetics of clarithromycin or its active metabolite, 14(
R
)-hydroxy-clarithromycin. However, the addition of clarithromycin statistically significantly altered the steady-state maximum observed plasma concentration and the area under the plasma concentration-time curve over a dosing interval for loratadine (+36 and +76%, respectively) and for descarboethoxyloratadine (DCL), the active metabolite of loratadine (+69 and +49%, respectively). Clarithromycin probably inhibits the oxidative metabolism of loratadine and DCL by the cytochrome P-450 3A subfamily. Electrocardiograms (
n
= 12) were obtained over 24-h periods at baseline and steady state (day 10). The mean maximum QTc interval and area under the QTc interval-time curve on day 10 were modestly increased (<3%) from baseline for all three regimens, but no QTc interval exceeded 439 ms for any subject. Elevated steady-state concentrations of loratadine and DCL do not appear to be associated with adverse cardiovascular effects related to prolongation of the QTc interval. Loratadine and clarithromycin were well tolerated, alone and in combination.
Flow Cytometric Assessment of the Postantibiotic Effect of Methicillin on
Staphylococcus aureus
Authors: Suller M. T. E. , Lloyd D. 
Published: October 2018

ABSTRACT

The postantibiotic effect (PAE) following a 2-h exposure of
Staphylococcus aureus
NCTC 6571 to methicillin (5× the MIC) was investigated with fluorescent probes, 5-cyano-2,3-di-4-tolyl tetrazolium chloride (CTC), an indicator of respiratory activity, and the membrane potential-sensitive compound bis-(1,3-dibutylbarbituric acid) trimethine oxonol [DiBAC
4
(3)]. Counts of the numbers of CFU on solid agar correlated well with information gained from the CTC and DiBAC
4
(3) fluorescence intensity distributions obtained by flow cytometry and revealed that the postantibiotic effect was 3.1 h. Due to the capacity of flow cytometry to provide information on the heterogeneity of a bacterial population, both fluorescent probes identified the emergence of an active subpopulation 4 h after removal of the methicillin, indicating the recovery of a small percentage of the population. After removal of the methicillin and resuspension of the cells in methicillin-free medium, a further decrease in the respiratory activity and the membrane integrity of the population was observed, although the CFU counts hardly varied, indicating continued antibiotic-induced damage. Also, CTC fluorescence measurements identified numerous subpopulations during the PAE period; this suggests that the PAE is complex, with individual organisms exhibiting various degrees of recovery. Flow cytometry thus provides a rapid and sensitive alternative to traditional techniques that have been used to study PAE, with the added advantage that physiological changes can be detected as they arise.
Novel Inhibitory Effects of γ-Glutamylcysteine Ethyl Ester against Human Immunodeficiency Virus Type 1 Production and Propagation
Authors: Kubota Satoshi , Shetty Shubhra , Zhang Huizhong , Kitahara Shigehisa , Pomerantz Roger J. 
Published: October 2018

ABSTRACTThe anti-human immunodeficiency virus type I (anti-HIV-1) effects of γ-glutamylcysteine ethyl ester (γ-GCE; TEI-2306) were examined in vitro. In initial studies using a vigorously HIV-1-producing human T-lymphocytic cell line, γ-GCE displayed a novel biphasic repressive effect on chronic HIV-1 infection that was unlike that of other glutathione prodrugs or other reported antioxidants. In high doses, up to a concentration of 2.5 mM, at which neither glutathione (GSH) nor another GSH precursor has shown inhibitory effects, γ-GCE potently inhibited the production of HIV-1 by a selective cytopathic effect against infected cells, while the viability and growth of uninfected cells were unaffected at the same γ-GCE concentrations. At lower concentrations (200 to 400 μM), γ-GCE significantly repressed the virus production from chronically HIV-1-expressing cells without affecting their viability. The discrepancy of the thresholds of the toxic doses between infected and uninfected cells was found to be more than 10-fold. Relatively high doses of γ-GCE, utilized in acute HIV-1 infection of T-lymphocytic cells, entirely blocked the propagation of HIV-1 and rescued the cells from HIV-1-induced cell death. Furthermore, γ-GCE at such concentrations was found to directly inhibit the infectivity of HIV-1 within 4 h. Repressive effects of γ-GCE on acute HIV-1 infection in human primary human peripheral blood mononuclear cells were also demonstrated. Here, the anti-HIV-1 strategy utilizing γ-GCE is removal of both HIV-1-producing cells and free infectious HIV-1 in vitro, in place of specific immunoclearance in vivo, which might lead to an arrest or slowing of viral propagation in HIV-1-infected individuals.
Killing of
Chlamydia trachomatis
by Novel Antimicrobial Lipids Adapted from Compounds in Human Breast Milk
Authors: Lampe M. F. , Ballweber L. M. , Isaacs C. E. , Patton D. L. , Stamm W. E. 
Published: October 2018

ABSTRACT

The development of new methods for prevention of sexually transmitted
Chlamydia trachomatis
infection is a top public health priority. Topical self-administered vaginal microbicides represent one such approach in which the organism is eradicated at the time of initial exposure. To this end, we examined the activity of five synthetic lipids adapted from naturally occurring compounds found in human breast milk.
C. trachomatis
serovar D or F elementary bodies were added to serial dilutions of the lipids and incubated for various times. Aliquots were then cultured in monolayers of McCoy cells, and inclusions were counted. A 7.5 mM concentration of 2-
O
-octyl-
sn
-glycerol completely prevented growth of
C. trachomatis
after 120 min of contact with the organism. The remaining lipids, 1-
O
-octyl-, 1-
O
-heptyl-, 2-
O
-hexyl-, and 1-
O
-hexyl-
sn
-glycerol, showed less activity. On electron microscopic examination, the lipids were shown to have disrupted the chlamydial inner membrane, allowing leakage of the cytoplasmic contents from the cell. Lipid activity was unaffected by the presence of 10% human blood or alterations in pH from 4.0 to 8.0, conditions reflecting those sometimes found in the vagina. Our results suggest that these lipids, especially 2-
O
-octyl-
sn
-glycerol, may be effective as topical microbicides in preventing the transmission of
C. trachomatis
. Further efficacy and toxicity studies with these lipids and assessment of their activity against other sexually transmitted disease pathogens are in progress.
Molecular Heterogeneity of the L-1 Metallo-β-Lactamase Family from
Stenotrophomonas maltophilia
Authors: Sanschagrin François , Dufresne Julien , Levesque Roger C. 
Published: October 2018

ABSTRACT

We have determined the nucleotide sequence of the
blaS
gene encoding the carbapenem-hydrolyzing L-1 β-lactamase from
Stenotrophomonas maltophilia
GN12873. Analysis of the DNA and deduced amino acid sequences identified a product of 290 amino acids. Comparisons of the L-1 amino acid sequence with those of other zinc β-lactamases showed 88.6% identity with the L-1 enzyme from
S. maltophilia
IID1275 and less than 20% identity with other class B metalloenzymes.