bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro activities of ramoplanin, selected glycopeptides, fluoroquinolones, and other antibiotics against clinical bloodstream isolates of gram-positive cocci
Authors: Lawrence T , Rotstein C , Beam T R , Gorzynski E A , Amsterdam D
Published: June 2012

The susceptibilities of 316 gram-positive bacteremic isolates to ramoplanin, vancomycin, and teicoplanin and seven other antibiotics were tested. Ramoplanin demonstrated MICs of < or = 0.25 microgram/ml for at least 99% of Staphylococcus aureus isolates and 100% of coagulase-negative staphylococci tested. For both oxacillin-susceptible and oxacillin-resistant S. aureus and coagulase-negative staphylococci, the activity of ramoplanin surpassed those of both vancomycin and teicoplanin. Ramoplanin and teicoplanin had comparable activities against enterococci and Streptococcus pneumoniae and were superior to vancomycin.
In vitro activity of RP 74501-RP 74502, a novel streptogramin antimicrobial mixture, against clinical isolates of Legionella species
Authors: Edelstein P H , Edelstein M A
Published: June 2012

Agar and broth microdilution MICs of RP 74501-RP 74502, a mixture of streptogramin antimicrobial agents that inhibited 90% of 22 Legionella strains tested, were 0.64 and 0.08 microgram/ml, respectively; respective erythromycin values were 1.0 and 0.12 microgram/ml. RP 74501-RP 74502 at 1 microgram/ml was more active than the same erythromycin concentration in a macrophage system for both L. pneumophila strains studied but at a lower concentration (0.25 microgram/ml) was much less active than erythromycin.
Postantibiotic effects of amikacin and ofloxacin on Mycobacterium fortuitum
Authors: Tsui S Y , Yew W W , Li M S , Chan C Y , Cheng A F
Published: June 2012

A study of postantibiotic effects (PAE) in vitro of amikacin and ofloxacin on Mycobacterium fortuitum isolates from sternotomy wounds by use of the dilution method for drug removal showed that both drugs exhibited good bactericidal activities, with the PAE of amikacin lasting from 13.5 to 27.6 h and the PAE of ofloxacin lasting from 1.2 to 5.0 h. These laboratory results concur with our experience of the efficacy of once-daily dosing with these drugs in the treatment of infections caused by M. fortuitum. These data may have therapeutic implications in guiding the scheduling of the administration of drugs in these infections, which require a long duration of therapy.
Genetic and biochemical analysis of a novel Ambler class A beta-lactamase responsible for cefoxitin resistance in Bacteroides species
Authors: Parker A C , Smith C J
Published: June 2012

A clinical isolate of Bacteroides vulgatus was resistant to tetracycline, clindamycin, ampicillin, cephaloridine, cefoxitin, and other beta-lactam antibiotics except imipenem. beta-Lactam resistance was mediated by a membrane-associated, clavulanate-sensitive cephalosporinase capable of degrading cephalosporins and penicillins. Cefoxitin also was degraded but at a slow rate. The cefoxitin resistance (Fxr) determinant was cloned from B. vulgatus genomic libraries that were prepared in Escherichia coli and then mated with Bacteroides fragilis for the identification of Fxr strains. Analysis of B. fragilis strains with the cloned Fxr determinant revealed the presence of a new beta-lactamase protein with the physical and enzymatic properties of the beta-lactamase found in the original B. vulgatus isolate. The beta-lactamase gene (cfxA) was subcloned on a 2.2-kb DraI-HindIII fragment, and the nucleotide sequence was determined. These results showed that cfxA encoded a protein of 321 amino acids and 35,375 molecular weight. Mutant strains in which the cfxA structural gene was disrupted by insertional inactivation lost both Fxr and beta-lactamase activity. Comparison of CfxA with other beta-lactamases showed a relationship with the active-site serine beta-lactamases in the Ambler molecular class A, although CfxA had apparently diverged significantly. This was exemplified by the substitution in CfxA at 13 of 25 amino acid residues previously identified as being invariant in class A beta-lactamases. These results suggest that CfxA may represent a new class A homology group which diverged very early.
Specific inhibition of the reverse transcriptase of human immunodeficiency virus type 1 and the chimeric enzymes of human immunodeficiency virus type 1 and type 2 by nonnucleoside inhibitors
Authors: Hizi A , Tal R , Shaharabany M , Currens M J , Boyd M R , Hughes S H , McMahon J B
Published: June 2012

We have studied the effects of four nonnucleoside inhibitors, including the novel natural product inhibitor calanolide A, on molecular chimeras containing complementary segments of human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) reverse transcriptases (RTs). All four compounds specifically inhibited the DNA polymerase activity of HIV-1 RT but had no apparent effect on the RNase H activity of this enzyme or on the DNA polymerase or RNase H activity of HIV-2 RT. Three of these compounds showed the generally expected patterns of resistance and susceptibility with the various chimeric RTs. However, the inhibition patterns of the chimeric RTs by calanolide A provided evidence that there is a segment between residues 94 and 157 in HIV-1 RT that is critical for inhibition. However, the data also suggest that there may be a second segment located between amino acids 225 and 427 in HIV-1 RT that is also important for specifying susceptibility to the drug.
Carnitine status and safety after administration of S-1108, a new oral cephem, to patients
Authors: Shimizu K , Saito A , Shimada J , Ohmichi M , Hiraga Y , Inamatsu T , Shimada K , Tanimura M , Fujita Y , Nishikawa T
Published: June 2012

The metabolism and clinical safety of the pivalic acid-containing antibiotic S-1108, an orally active pro-drug cephalosporin, were investigated to assess the clinical effects, with special emphasis on the influence of carnitine consumption in 15 patients with various infectious diseases receiving S-1108 three times a day at a 300- or 600-mg total daily dose for 3 to 7 days. The free carnitine concentrations in plasma were greatly reduced to approximately 65% of pretreatment levels, and the plasma pivaloylcarnitine (the main metabolite of pivaloyloxymethyl ester) concentrations were increased during the 200-mg (three times a day) regimens but returned to the pretreatment levels within 3 to 5 days after the cessation of treatment. In three elderly patients with declining renal function (creatinine clearance rate, 31 to 50 ml/min), the acylcarnitine/free carnitine ratio increased from 0.1 to 0.4 up to 0.7 to 1.5 at day 5 during the 7-day treatment, showed a tendency to decrease, and then returned to the pretreatment ratio 4 days after discontinuation of the drug. The degree of free carnitine reduction and increase of the acylcarnitine/free carnitine ratio depended mostly on the dose and the duration of S-1108 treatment. The increased acylcarnitine/free carnitine ratio in elderly patients was due to reduction of the free carnitine concentration in plasma and mainly to the retardation of nontoxic pivaloylcarnitine excretion. This study indicated that there was a decrease in free carnitine levels in plasma, but there were no clinical symptoms or adverse effects associated with carnitine reduction in patients during the 7-day multiple administration of S-1108.
Development of a population pharmacokinetic model and optimal sampling strategies for intravenous ciprofloxacin
Authors: Forrest A , Ballow C H , Nix D E , Birmingham M C , Schentag J J
Published: June 2012

Data obtained from 74 acutely ill patients treated in two clinical efficacy trials were used to develop a population model of the pharmacokinetics of intravenous (i.v.) ciprofloxacin. Dosage regimens ranged between 200 mg every 12 h and 400 mg every 8 h. Plasma samples (2 to 19 per patient; mean +/- standard deviation = 7 +/- 5) were obtained and assayed (by high-performance liquid chromatography) for ciprofloxacin. These data and patient covariates were modelled by iterative two-stage analysis, an approach which generates pharmacokinetic parameter values for both the population and each individual patient. The final model was used to implement a maximum a posteriori-Bayesian pharmacokinetic parameter value estimator. Optimal sampling theory was used to determine the best (maximally informative) two-, three-, four-, five-, and six-sample study designs (e.g., optimal sampling strategy 2 [OSS2] was the two-sample strategy) for identifying a patient's pharmacokinetic parameter values. These OSSs and the population model were evaluated by selecting the relatively rich data sets, those with 7 to 10 samples obtained in a single dose interval (n = 29), and comparing the parameter estimates (obtained by the maximum a posteriori-Bayesian estimator) based on each of the OSSs with those obtained by fitting all of the available data from each patient. Distributional clearance and apparent volumes were significantly related to body size (e.g., weight in kilograms or body surface area in meters squared); plasma clearance (CLT in liters per hour) was related to body size and renal function (creatinine clearance [CLCR] in milliliters per minute per 1.73 m2) by the equation CLT = (0.00145.CLCR + 0.167).weight. However, only 30% of the variance in CLT was explained by this relationship, and no other patient covariates were significant. Compared with previously published data, this target population had smaller distribution volumes (by 30%; P < 0.01) and CLT (by 44%; P < 0.001) than weight- and CLCR- matched stable volunteers. OSSs provided parameter estimates that showed good to excellent estimates of CLT (or area under the concentrations-time curve [AUC]) were unbiased and precise (e.g., r2 for AUC for all data versus AUC for OSS2 was > 0.99) and concentration-time profiles were accurately reconstructed. These results will be used to model the pharmacodynamic relationships between ciprofloxacin exposure and response and to aid in developing algorithms for individual optimization of ciprofloxacin dosage regimens.
Pharmacodynamics of intravenous ciprofloxacin in seriously ill patients
Authors: Forrest A , Nix D E , Ballow C H , Goss T F , Birmingham M C , Schentag J J
Published: June 2012

Seventy-four acutely ill patients were treated with intravenous ciprofloxacin at dosages ranging between 200 mg every 12 h and 400 mg every 8 h. A population pharmacokinetic-pharmacodynamic analysis relating drug exposure (and other factors) to infectious outcome was performed. Plasma samples were obtained and assayed for ciprofloxacin by high-performance liquid chromatography. Samples from patients were frequently cultured so that the day of bacterial eradication could be determined. The pharmacokinetic data were fitted by iterative two-stage analysis, assuming a linear two-compartment model. Logistic regression was used to model ciprofloxacin exposure (and other potential covariates) versus the probabilities of achieving clinical and microbiologic cures. The same variables were also modelled versus the time to bacterial eradication by proportional hazards regression. The independent variables considered were dose, site of infection, infecting organism and the MIC for it, percent time above the MIC, peak, peak/MIC ratio, trough, trough/MIC ratio, 24-h area under the concentration-time curve (AUC), AUC/MIC ratio (AUIC), presence of other active antibacterial agents, and patient characteristics. The most important predictor for all three measures of ciprofloxacin pharmacodynamics was the AUIC. A 24-h AUIC of 125 SIT-1.h (inverse serum inhibitory titer integrated over time) was found to be a significant breakpoint for probabilities of both clinical and microbiologic cures. At an AUIC below 125 (19 patients), the percent probabilities of clinical and microbiologic cures were 42 and 26%, respectively. At an AUIC above 125 (45 patients), the probabilities were 80% (P < 0.005) and 82% (P < 0.001), respectively. There were two significant breakpoints in the time-to-bacterial-eradication data. At an AUIC below 125 (21 patients), the median time to eradication exceeded 32 days; at an AUIC of 125 to 250 (15 patients), time to eradication was 6.6 days: and at AUIC above 250 (28 patients), the median time to eradication was 1.9 days (groups differed; P < 0.005). These findings, when combined with pharmacokinetic data reported in the companion article, provide the rationale and tools needed for targeting the dosage of intravenous ciprofloxacin to individual patients' pharmacokinetics and their bacterial pathogens' susceptibilities. An a priori dosing algorithm (based on MIC, patient creatine clearance and weight, and the clinician-specified AUIC target) was developed. This approach was shown, retrospectively, to be more precise than current guidelines, and it can be used to achieve more rapid bacteriologic and clinical responses to ciprofloxacin, as a consequence of targeting the AUIC.
Standardized peripheral blood mononuclear cell culture assay for determination of drug susceptibilities of clinical human immunodeficiency virus type 1 isolates. The RV-43 Study Group, the AIDS Clinical Trials Group Virology Committee Resistance Working Group
Authors: Japour A J , Mayers D L , Johnson V A , Kuritzkes D R , Beckett L A , Arduino J M , Lane J , Black R J , Reichelderfer P S , D'Aquila R T
Published: June 2012

A standardized antiviral drug susceptibility assay for clinical human immunodeficiency virus type 1 (HIV-1) isolates has been developed for use in clinical trials. The protocol is a two-step procedure that first involves cocultivation of patient infected peripheral blood mononuclear cells (PBMC) with seronegative phytohemagglutinin-stimulated donor PBMC to obtain an HIV-1 stock. The virus stock is titrated for viral infectivity (50% tissue culture infective dose) by use of serial fourfold virus dilutions in donor PBMC. A standardized inoculum of 1,000 50% tissue culture infective doses per 10(6) cells is used in the second step of the procedure to acutely infect seronegative donor PBMC in a 7-day microtiter plate assay with triplicate wells containing zidovudine (ZDV) concentrations ranging from 0 to 5.0 microM. The ZDV 50% inhibitory concentrations (IC50) for reference ZDV-susceptible and ZDV-resistant HIV-1 isolates ranged from 0.002 to 0.113 microM and from 0.15 to > 5.0 microM, respectively. Use of this consensus protocol reduced interlaboratory variability for ZDV IC50 determinations with reference HIV-1 isolates. Among eight laboratories, the coefficient of variation ranged from 0.85 to 1.25 with different PBMC protocols and was reduced to 0.39 to 0.98 with the standardized assay. Among the clinical HIV-1 isolates assayed by the standardized drug susceptibility assay, the median ZDV IC50 increased gradually with more ZDV therapy. This protocol provides an efficient and reproducible means to assess the in vitro susceptibility to antiretroviral agents of virtually all clinical HIV-1 isolates.
Clonal viability measurements on Plasmodium falciparum to assess in vitro schizonticidal activity of leupeptin, chloroquine, and 5-fluoroorotate
Authors: Young R D , Rathod P K
Published: June 2012

Until now, the in vitro activity of potential antimalarial agents has been evaluated primarily by monitoring decreases in parasite proliferation. These traditional assays do not distinguish between compounds that arrest proliferation of parasites and compounds that kill them. In this report, a more complex in vitro cytocidal assay for Plasmodium falciparum is described. This assay measures the clonal viability of P. falciparum after the parasites have been treated with an antimalarial agent. The new assay was used to assess cytocidal activities of three antimalarial agents that work through unrelated mechanisms. Leupeptin, a protease inhibitor, arrested the proliferation of W2 clones of P. falciparum at a MIC of 50 microM, but at least 80% of leupeptin-treated cells were viable as judged by the cytocidal assay. On the other hand, chloroquine at 1 microM, its MIC for W2 cells, not only arrested parasite proliferation but also killed more than 99% of the cells. Earlier studies had shown that treatment of P. falciparum with 100 nM 5-fluoroorotate for 48 h was sufficient to inhibit parasite proliferation and parasite thymidylate synthase but not enough to cause significant incorporation of 5-fluoropyrimidines in parasite nucleic acids. By using the new schizonticidal assay, these conditions were found to be necessary and sufficient to kill all parasites in culture. Results of these studies are consistent with the hypothesis that 5-fluoroorotate-based inactivation of P. falciparum thymidylate synthase triggers a lethal mechanism against malarial parasites.
U-90152, a potent inhibitor of human immunodeficiency virus type 1 replication
Authors: Dueweke T J , Poppe S M , Romero D L , Swaney S M , So A G , Downey K M , Althaus I W , Reusser F , Busso M , Resnick L
Published: June 2012

Bisheteroarylpiperazines are potent inhibitors of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). We describe a novel bisheteroarylpiperazine, U-90152 [1-(5-methanesulfonamido-1H-indol-2-yl-carbonyl)-4-[3-(1-methyl eth yl-amino)pyridinyl]piperazine], which inhibited recombinant HIV-1 RT at a 50% inhibitory concentration (IC50) of 0.26 microM (compared with IC50s of > 440 microM for DNA polymerases alpha and delta). U-90152 blocked the replication in peripheral blood lymphocytes of 25 primary HIV-1 isolates, including variants that were highly resistant to 3'-azido-2',3'-dideoxythymidine (AZT) or 2',3'-dideoxyinosine, with a mean 50% effective dose of 0.066 +/- 0.137 microM. U-90152 had low cellular cytotoxicity, causing less than 8% reduction in peripheral blood lymphocyte viability at 100 microM. In experiments assessing inhibition of the spread of HIV-1IIIB in cell cultures, U-90152 was much more effective than AZT. When approximately 500 HIV-1IIIB-infected MT-4 cells were mixed 1:1,000 with uninfected cells, 3 microM AZT delayed the evidence of rapid viral growth for 7 days. In contrast, 3 microM U-90152 totally prevented the spread of HIV-1, and death and/or dilution of the original inoculum of infected cells prevented renewed viral growth after U-90152 was removed at day 24. The combination of U-90152 and AZT, each at 0.5 microM, also totally prevented viral spread. Finally, although the RT amino acid substitutions K103N (lysine 103 to asparagine) and Y181C (tyrosine 181 to cysteine), which confer cross-resistance to several nonnucleoside inhibitors, also decrease the potency of U-90152, this drug retains significant activity against these mutant RTs in vitro (IC50s, approximately 8 microgramM).
Comparative study of bioavailabilities and pharmacokinetics of clindamycin in healthy volunteers and patients with AIDS
Authors: Gatti G , Flaherty J , Bubp J , White J , Borin M , Gambertoglio J
Published: June 2012

The absolute oral bioavailability and pharmacokinetics of clindamycin administered to 16 healthy volunteers and 16 patients with AIDS were compared. Clindamycin was given intravenously (i.v.) (Cleocin phosphate) at a dose of 600 mg as a 25-min infusion and orally (Cleocin hydrochloride) by use of a crossover design in both study groups. Plasma samples were analyzed by gas-liquid chromatography. Plasma drug clearance and volume of distribution at the steady state following the i.v. dose differed between study groups. The clearances were 0.27 +/- 0.06 liter/h/kg in healthy volunteers and 0.21 +/- 0.06 liter/h/kg in AIDS patients (P = 0.014; Mann-Whitney U test); the volumes of distribution at the steady state were 0.79 +/- 0.13 and 0.66 +/- 0.12 liter/kg in healthy volunteers and AIDS patients, respectively (P = 0.005). The elimination half-life did not differ between the two groups. The bioavailability of clindamycin capsules in AIDS patients was approximately 1.5 times that in healthy volunteers (0.53 +/- 0.14 versus 0.75 +/- 0.20; P = 0.002). Peak concentrations following the oral dose were higher in AIDS patients as well (7.7 +/- 2.5 versus 5.3 +/- 1.0 mg/liter; P = 0.0008). Three AIDS patients experienced severe diarrhea following the oral dose; four patients had mild diarrhea following the i.v. dose. No adverse effects were reported by the healthy volunteers. The pharmacokinetic parameters observed in this study for AIDS patients may be useful for the consideration of clindamycin dosage regimens in patients treated for toxoplasmic encephalitis. These findings suggest that the effect of AIDS on drug disposition deserves further investigation, particularly for orally administered drugs.
Pharmacokinetics of the anti-human immunodeficiency virus nucleoside analog stavudine in cynomolgus monkeys
Authors: Kaul S , Dandekar K A
Published: June 2012

Stavudine was administered (15 mg/kg of body weight) intravenously and orally to two monkeys in a randomized crossover study. Plasma and urine samples were analyzed for stavudine by high-performance liquid chromatography, and pharmacokinetic parameters were derived by a noncompartmental method. Total body clearance of stavudine was 0.64 liters/h/kg, with a steady-state volume of distribution of 0.68 liters/kg, a terminal half-life of 0.83 h, a urinary recovery of 44%, and an oral bioavailability of 80%. These values were reasonably similar to those reported for patients with AIDS or AIDS-related complex.
Derivation and characterization of a quinapyramine-resistant clone of Trypanosoma congolense
Authors: Ndoutamia G , Moloo S K , Murphy N B , Peregrine A S
Published: June 2012

Over a period of 208 days a quinapyramine-resistant population was derived in vivo from a quinapyramine-susceptible clone of Trypanosoma congolense: IL 1180. While the dose of quinapyramine sulfate required to cure 50% of mice infected with the parental clone was 0.23 mg/kg of body weight, the 50% curative dose for the resistant derivative, IL 1180/Stabilate 12, was greater than 9.6 mg/kg. This approximately 40-fold increase in resistance to quinapyramine was shown to be associated with an 8-fold increase in resistance to isometamidium, a 28-fold increase in resistance to homidium, and a 5.5-fold increase in resistance to diminazene. Cross-resistance to homidium and diminazene was also demonstrated in goats. Two clones derived from the drug-resistant derivative underwent cyclical development in Glossina morsitans centralis, producing mature infection rates of 39.6 and 23.9%. Thus, induction of resistance to quinapyramine in T. congolense IL 1180 was associated with cross-resistance to isometamidium, homidium, and diminazene and did not compromise the population's ability to undergo full cyclical development in tsetse flies.
Use of an in vivo system to determine the G418 resistance phenotype of bloodstream-form Trypanosoma brucei brucei transfectants
Authors: Murphy N B , Muthiani A M , Peregrine A S
Published: June 2012

We determined the level of susceptibility of Trypanosoma brucei brucei to the aminoglycoside G418 in vivo and demonstrated that it is possible to select for G418-resistant transfected T. brucei brucei bloodstream parasites in a mouse host by inoculating the drug intraperitoneally at doses between 40 and 80 mg/kg of body weight daily for 3 days. The ability to select for transfectants in vivo offers new possibilities for studies on genetic recombination in these parasites.
Influence of therapeutic plasmapheresis on elimination of ceftiaxone
Authors: Bakken J S , Cavalieri S J , Gangeness D , Kubat T , Pollack J R
Published: June 2012

To study the plasma elimination rate of ceftriaxone given to patients undergoing plasmapheresis, a single 2-g intravenous dose of ceftriaxone was given to 11 patients who underwent plasmapheresis 3 h (early group) or 15 h (late group) later. Even though the early patient group had twofold more ceftriaxone removed than the late group, all individual patients had 24-h ceftriaxone levels of 9 micrograms/ml or higher. We conclude that patients undergoing plasmapheresis lasting 150 min or less may safely be treated with 2 g of ceftriaxone once daily without risking periods of subtherapeutic plasma ceftriaxone levels.
Mobilization of the penicillinase gene in Enterococcus faecalis
Authors: Chow J W , Perri M B , Thal L A , Zervos M J
Published: June 2012

Enterococcus faecalis SF4855 is a beta-lactamase-producing isolate resistant to high levels of gentamicin, with determinants for these resistances on the chromosome. SF4855 transferred both determinants into E. faecalis FA2-2 and UV202 at a frequency of 10(-9) in the presence of the MLS plasmid pYN120. beta-Lactamase and gentamicin resistance probes hybridized to three locations on the chromosome of FA2-2 transconjugants on contour-clamped homogeneous electric field electrophoresis. The study results suggest mobilization of the beta-lactamase determinant.
Antimicrobial susceptibilities of enterococci isolated from hospitalized patients
Authors: Venditti M , Tarasi A , Gelfusa V , Nicastri E , Penni A , Martino P
Published: June 2012

One hundred and one isolates of Enterococcus species isolated recently from hospitalized patients were evaluated in vitro for antibiotic susceptibility. Teicoplanin and mideplanin were the most active agents, followed by ramoplanin, vancomycin, ciprofloxacin, ampicillin, and imipenem. High-level resistance to gentamicin (MIC > 500 micrograms/ml) and/or streptomycin (MIC > 2,000 micrograms/ml) was found in 60 isolates. High-level resistance to ampicillin (MIC > or = 16 micrograms/ml) was found in 17 isolates. MBC studies revealed that ramoplanin possesses significant bactericidal activity.
Effects of probenecid on the pharmacokinetics of allopurinol riboside
Authors: Were J B , Shapiro T A
Published: June 2012

Allopurinol riboside is an experimental agent for the treatment of leishmaniasis and American trypanosomiasis. Previous studies showed that after oral administration, unexpectedly low levels of allopurinol riboside in plasma are attributable to incomplete absorption and rapid renal clearance. In this randomized, crossover evaluation in healthy volunteers, probenecid reduces the renal clearance of allopurinol riboside, extends the half-life of allopurinol riboside in plasma, and triples the levels of allopurinol riboside in plasma.
Biochemical properties of a carbapenem-hydrolyzing beta-lactamase from Enterobacter cloacae and cloning of the gene into Escherichia coli
Authors: Nordmann P , Mariotte S , Naas T , Labia R , Nicolas M H
Published: June 2012

A clinical isolate of Enterobacter cloacae, strain NOR-1, exhibited resistance to imipenem and remained susceptible to extended-spectrum cephalosporins. Clavulanic acid partially restored the susceptibility of the strain to imipenem. Two beta-lactamases with isoelectric points (pI) of 6.9 and > 9.2 were detected in strain E. cloacae NOR-1; the higher pI corresponded to AmpC cephalosporinase. Plasmid DNA was not detected in E. cloacae NOR-1 and imipenem resistance could not be transferred into Escherichia coli JM109. The carbapenem-hydrolyzing beta-lactamase gene was cloned into plasmid pACYC184. One recombinant plasmid, pPTN1, harbored a 5.3-kb Sau3A fragment from E. cloacae NOR-1 expressing the carbapenem-hydrolyzing beta-lactamase. This enzyme (pI 6.9) hydrolyzed ampicillin, cephalothin, and imipenem more rapidly than it did meropenem and aztreonam, but it hydrolyzed extended-spectrum cephalosporins only weakly and did not hydrolyze cefoxitin. Hydrolytic activity was partially inhibited by clavulanic acid, sulbactam, and tazobactam, was nonsusceptible to chelating agents such as EDTA and 1,10-o-phenanthroline, and was independent of the presence of ZnCl2. Its relative molecular mass was 30,000 Da. Induction experiments concluded that the carbapenem-hydrolyzing beta-lactamase biosynthesis was inducible by cefoxitin and imipenem. Subcloning experiments with HindIII partial digests of pPTN1 resulted in a recombinant plasmid, designated pPTN2, which contained a 1.3-kb insert from pPTN1 and which conferred resistance to beta-lactam antibiotics. Hybridization studies performed with a 1.2-kb HindIII fragment from pPtN2 failed to determine any homology with ampC of E. cloacae, with other known beta-lactamase genes commonly found in members of the family Enterobacteriaceae (bla(TEM-1)) and bla(SHV-3) derivatives), and with previously described carbapenemase genes such as those from Xanthomonas maltophilia, Bacillus cereus, Bacteroides fragilis (cfiA), and Aeromonas hydrophila (cphA). This work describing the biochemical properties of a novel chromosome-encoded beta-lactamase from E. cloacae indicates that this enzyme differs from all the previously described carbapenemases. This is the first reported cloning of a carbapenem-hydrolyzing gene from a member of the family Enterobacteriaceae.
A nonnucleoside reverse transcriptase inhibitor active on human immunodeficiency virus type 1 isolates resistant to related inhibitors
Authors: Goldman M E , O'Brien J A , Ruffing T L , Schleif W A , Sardana V V , Byrnes V W , Condra J H , Hoffman J M , Emini E A
Published: June 2012

Pyridinone derivatives are potent and specific inhibitors of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) and HIV-1 replication in cell culture. However, the potential clinical usefulness of these compounds as monotherapeutic agents may be limited by the selection of inhibitor-resistant viral variants. Resistance in cell culture is due primarily to mutational alterations at RT amino acid residues 103 and 181. A recombinant HIV-1 RT containing both of these mutations was used to screen a panel of pyridinone analogs for inhibitory activity. L-696,229 and L-697,661, pyridinones currently undergoing clinical evaluation, were more than 4,000-fold weaker against the mutant enzyme than against the wild-type enzyme. In contrast, one derivative of L-696,229, L-702,019 (3-[2-(4,7-dichlorobenzoxazol-2-yl)ethyl]-5-ethyl-6-methylpyrid in-2(1H)-thione), showed only three-fold different potencies against the two enzymes. L-702,019 was also a potent inhibitor of the replication of mutant HIV-1 containing the individual mutations at amino acid 103 or 181 as well as of clinical isolates resistant to L-697,661 and L-696,229. Isolation and analysis of resistant viral variants in cell culture showed that significant resistance to L-702,019 could be engendered only by multiple amino acid substitutions in RT. Accordingly, these studies demonstrated the potential of identifying second-generation specific HIV-1 RT inhibitors that can overcome the viral resistance selected by the first generation of inhibitors.
Oxidant-scavenging activities of ampicillin and sulbactam and their effects on neutrophil functions
Authors: Gunther M R , Mao J , Cohen M S
Published: June 2012

Luminol-enhanced luminescence is a method used to measure formation of reactive oxygen intermediates important in the ability of neutrophils to kill microbes. Several studies have demonstrated that under some conditions of incubation, ampicillin can inhibit neutrophil-derived luminol-enhanced luminescence. We evaluated the mechanism(s) by which ampicillin inhibited the luminescent response of stimulated neutrophils. We also investigated sulbactam, a beta-lactamase inhibitor which has been given in combination with ampicillin and other beta-lactam antibiotics to increase their spectra, for possible similar effects. Both ampicillin and sulbactam attenuated luminol-enhanced luminescence by approximately 40%. Superoxide production was not prevented by added ampicillin, nor was superoxide scavenged by it. Myeloperoxidase reacts with H2O2 and Cl- to generate OCl-, which is believed to be the oxidizer of luminol that is primarily responsible for enhancement of neutrophil-derived luminescence. Hydroxyl radicals (HO.), which may also oxidize luminol, resulting in luminescence, can be formed from O2- and H2O2 via either myeloperoxidase-dependent (involving intermediate OCl-) or myeloperoxidase-independent (through a metal ion catalyst) reactions. Ampicillin scavenged H2O2 and OCl- and prevented 95% of Fenton reaction-generated HO. from reacting with 5,5-dimethyl-1-pyrroline-N-oxide. Sulbactam was found to scavenge OCl- and HO., but less avidly than ampicillin did. Neither ampicillin nor sulbactam inhibited myeloperoxidase activity. Sublethal concentrations of sulbactam had no significant effect on neutrophil killing of Staphylococcus aureus and Escherichia coli. Our results demonstrate a mechanism(s) by which ampicillin inhibits luminol-enhanced luminescence from stimulated neutrophils, namely, through scavenging of the oxidant(s) primarily responsible for the generation of luminescence.
Selective inhibition of the bacterial translocase reaction in peptidoglycan synthesis by mureidomycins
Authors: Inukai M , Isono F , Takatsuki A
Published: June 2012

Mureidomycins (MRDs) A and C inhibited strongly the formation of undecaprenyl pyrophosphoryl N-acetylmuramyl-pentapeptide (lipid intermediate I), which is an intermediate in bacterial peptidoglycan synthesis (50% inhibitory concentration [IC50] of MRD A, 0.05 microgram/ml). However, they did not inhibit the formation of dolichyl pyrophosphoryl N-acetylglucosamine (Dol-p-p-GlcNAc), dolichyl phosphoryl glucose, or dolichyl phosphoryl mannose, the precursors for mammalian glycoprotein synthesis, or the formation in Bacillus subtilis of lipid-linked N-acetylglucosamine for teichoic acid synthesis (IC50s, > 100 micrograms/ml). In contrast, tunicamycin (TCM) inhibited strongly the formation of Dol-p-p-GlcNAc (IC50, 0.03 microgram/ml) but inhibited weakly the formation of bacterial lipid intermediate I (IC50, 44 micrograms/ml). When the effects of MRDs A and C and TCM on the growth of mammalian cells were compared, MRDs did not show any toxicity, even at 1,000 micrograms/ml, whereas TCM inhibited the growth of BALB/3T3 cells at 10 micrograms/ml. On the basis of these results, it was concluded that MRDs are the first specific and potent inhibitors of the translocase reaction in bacterial peptidoglycan synthesis, showing a high level of toxicity against bacteria and a low level of toxicity against mammalian cells. A specific inhibitor of translocase could be a potent antibiotic with highly selective toxicity.
Distribution of mec regulator genes in methicillin-resistant Staphylococcus clinical strains
Authors: Suzuki E , Kuwahara-Arai K , Richardson J F , Hiramatsu K
Published: June 2012

The distributions of the mec regulator genes mecI and mecR1, which were identified on the chromosome of mecA-carrying Staphylococcus aureus N315, in methicillin-resistant staphylococci isolated in Japan and various countries were studied. Screening by dot blot hybridization by using polymerase chain reaction (PCR)-amplified probes revealed that at least the 5'-end region of the mecR1 gene was present in all strains tested, whereas about 40% of the strains were negative for the mecI gene. The data suggested that these regulator genes were the original components of the additional mec region DNA of methicillin-resistant S. aureus as well as methicillin-resistant, coagulase-negative staphylococci of seven staphylococcal species (S. epidermidis, S. haemolyticus, S. hominis, S. sciuri, S. capitis, S. caprae, and S. warneri). The mecI gene, which presumably codes for the repressor protein of the mecA gene, was found to harbor a point mutation in all six mecI-positive methicillin-resistant S. aureus strains, and their basal level of mecA gene transcription was elevated compared with that of strain N315, which harbors a presumably intact counterpart of the mecI gene. The data suggested that the mecI gene encodes for a strong repressor function on mecA gene transcription and is deleted or mutated in clinical methicillin-resistant S. aureus strains with high levels of resistance to methicillin.
Inhibition of Pneumocystis carinii dihydropteroate synthetase by para-acetamidobenzoic acid: possible mechanism of action of isoprinosine in human immunodeficiency virus infection
Authors: Kovacs J A , Powell F , Voeller D , Allegra C J
Published: June 2012

Isoprinosine has been reported to decrease progression to AIDS, primarily by preventing Pneumocystis carinii pneumonia (PCP), in human immunodeficiency virus-infected patients, but the mechanism of action is unknown. para-Acetamidobenzoic acid (PAcBA), one component of isoprinosine, is structurally related to para-aminobenzoic acid (PABA), a precursor of de novo folate synthesis. This pathway is known to be important for P. carinii because sulfonamides, which are effective anti-P. carinii agents, inhibit incorporation of PABA into folate precursors by the enzyme dihydropteroate synthetase (DHPS). Inhibition of P. carinii DHPS by PAcBA was investigated by using two assays. In short-term cultures of P. carinii from rats, [3H]PABA incorporation into reduced folates was inhibited by both isoprinosine (mean +/- standard error 50% inhibitory concentration [IC50], 20 +/- 8.4 microM) and PAcBA free acid (IC50, 240 +/- 100 microM); a soluble PAcBA salt was more potent than PAcBA free acid alone (IC50, 29 +/- 48 microM). The activity of PAcBA free acid was confirmed in a cell-free DHPS inhibition assay (IC50, 120 +/- 120 microM). Inosine and dimethylaminopropanol, two other components of isoprinosine, were poor inhibitors of PABA incorporation (IC50, > 1,000 microM). PAcBA free acid also showed activity in inhibiting the DHPS of Toxoplasma gondii, but was a poor inhibitor of the DHPSs of Escherichia coli and Saccharomyces cerevisiae. In a rat model of PCP, the PAcBA salt administered intraperitoneally demonstrated no activity against established PCP either alone or when used in combination with trimethoprim; the lack of efficacy in this model may be due to the rapid metabolism of the drug. Prevention of PCP by PaCBA through inhibition of P. carinii DHPS may explain the activity of isoprinosine in decreasing the progression to AIDS in human immunodeficiency virus-infected patients.
Novel gyrA point mutation in a strain of Escherichia coli resistant to fluoroquinolones but not to nalidixic acid
Authors: Cambau E , Bordon F , Collatz E , Gutmann L
Published: June 2012

We have previously described a clinical isolate of Escherichia coli (Q2) that is highly resistant to fluoroquinolones (MIC of ciprofloxacin, 16 micrograms/ml) but susceptible to nalidixic acid (MIC of nalidixic acid, 4 micrograms/ml) (N. Moniot-Ville, J. Guibert, N. Moreau, J.F. Acar, E. Collatz, and L. Gutmann, Antimicrob. Agents Chemother. 35:519-523, 1991). Transformation of strain Q2 with a plasmid carrying the wild-type gyrA gene from E. coli K-12(pAFF801) resulted in a 32-fold decrease in the MIC of ciprofloxacin, suggesting that at least one mutation in gyrA was involved in the resistance of Q2. Intragenic gyrA fragments of 668 and 2,500 bp from strain Q2 were amplified by the polymerase chain reaction. We sequenced the 668-bp fragment and identified a single novel point mutation (transition from G to A at position 242), leading to an amino acid substitution (Gly-81 to Asp) in the gyrase A subunit. We constructed hybrid plasmids by substituting either the 668-bp fragment or the 2,500-bp fragment from Q2 DNA, both of which contained the gyrA point mutation, for the corresponding fragments in wild-type gyrA (2,625 bp) of E. coli K-12. When introduced into E. coli KNK453 (gyrA temperature sensitive), both plasmids conferred an eightfold increase in the MIC of ciprofloxacin, but only a twofold increase in the MIC of nalidixic acid. When introduced into E. coli Q2, neither plasmid conferred any change in the MICs of ciprofloxacin or nalidixic acid, suggesting that only the point mutation found in gyrA was involved in the resistance that we observed.
Effect of 3'-azido-3'-deoxythymidine on human immunodeficiency virus type 1 replication in human fetal brain macrophages
Authors: Geleziunas R , Arts E J , Boulerice F , Goldman H , Wainberg M A
Published: June 2012

We investigated whether cells derived from the fetal central nervous system can support productive infection by a human immunodeficiency virus type 1 (HIV-1) isolate termed UHC-1, produced by a cellular clone derived from HIV-1 strain HIV-IIIB chronically infected U-937 promonocytic cells, and what the effect of nucleoside analogs might be on viral replication in this system. Fractionation of human fetal brain tissue into two different populations, enriched for either astrocytes or macrophages, showed that only the latter were able to support productive UHC-1 replication and generation of detectable progeny virus. Pretreatment of fetal brain macrophages with either of two nucleoside analogs, 3'-azido-3'-deoxythymidine (AZT) or the (-) enantiomer of 2'-deoxy-3'-thiacytidine, efficiently blocked production of progeny virus. Generation of unintegrated proviral DNA and HIV-1 transcripts were inhibited by pretreatment of fetal brain macrophages with 1 microM AZT. Administration of AZT at 24 h postinfection led to a slight reduction in viral transcript levels and viral progeny production by day 15 postinfection; however, brain macrophages under these conditions did not contain detectable amounts of unintegrated viral DNA. These results suggest that AZT may interfere with the accumulation of unintegrated HIV-1 DNA in brain macrophages. This is the first demonstration that nucleoside analogs are able to block HIV-1 replication in primary cultures of brain cells.
Aerosol amphotericin B for prevention of invasive pulmonary aspergillosis
Authors: Beyer J , Barzen G , Risse G , Weyer C , Miksits K , Dullenkopf K , Huhn D , Siegert W
Published: June 2012

The pharmacokinetics and applicability of aerosol amphotericin B administrations were studied in 40 neutropenic patients and 4 healthy volunteers. Particle size was measured and pulmonary deposition was demonstrated by radioisotope studies. Inhalations were easy to administer and were well tolerated, with minimal systemic absorption of the drug.
Potent inhibition of Epstein-Barr virus by phosphorothioate oligodeoxynucleotides without sequence specification
Authors: Yao G Q , Grill S , Egan W , Cheng Y C
Published: June 2012

We found that 28-mer phosphorothioate oligodeoxynucleotides (S-oligos) with and without sequence specificity complementary to Epstein-Barr virus (EBV) genes are potent inhibitors of EBV replication in cell culture. The decrease in the amount of EBV DNA, the activity of intracellular viral DNA polymerase, and virus production were dose dependent, with a 90% inhibitory dose of approximately 0.5 microM. No inhibition of cell growth was observed with the S-oligos at concentrations up to 20 microM. The mechanism of action appears to be the inhibition of EBV DNA synthesis. The reversibility of anti-EBV action is dependent on the dose and duration of drug exposure. S-oligos should be considered a new class of anti-EBV agents.
In vitro susceptibility of Borrelia burgdorferi to 11 antimicrobial agents
Authors: Levin J M , Nelson J A , Segreti J , Harrison B , Benson C A , Strle F
Published: June 2012

The in vitro susceptibility of Borrelia burgdorferi to 11 antimicrobial agents was investigated. The antimicrobial agents evaluated included ceftizoxime, FK037, cefotaxime, dirithromycin, clarithromycin and its metabolite 14-hydroxy-clarithromycin, erythromycin, doxycycline, amoxicillin, ciprofloxacin, and ofloxacin. Isolates of B. burgdorferi tested included two reference strains (B31 and ATCC 53899), six isolates from the midwestern United States, and three from Europe. A broth macrodilution method was used to determine MICs and MBCs. B. burgdorferi was inhibited by < or = 0.5 micrograms of each of the agents except the quinolones per ml. The MBCs for 90% of strains tested of ceftizoxime, FK037, clarithromycin, 14-OH clarithromycin, and dirithromycin (< or = 1.0 microgram of each per ml) were superior to those of amoxicillin (2.0 micrograms/ml) and doxycycline (4.0 micrograms/ml). Further in vivo studies are warranted to determine whether these agents may be efficacious in the treatment of Lyme borreliosis.
Comparison of ampicillin-sulbactam with vancomycin for treatment of experimental endocarditis due to a beta-lactamase-producing, highly gentamicin-resistant isolate of Enterococcus faecalis
Authors: Lavoie S R , Wong E S , Coudron P E , Williams D S , Markowitz S M
Published: June 2012

Increasing antibiotic resistance in the enterococci, including the capacity for beta-lactamase production and the development of high-level aminoglycoside resistance, has complicated the treatment of serious enterococcal infections, which often require synergistic antibiotic combinations for cure. We utilized the rabbit model of aortic valve endocarditis to investigate the effects of various antibiotics, alone and in combination, against a multiply antibiotic-resistant isolate of Enterococcus faecalis. Female New Zealand White rabbits were infected with either a beta-lactamase-producing, gentamicin-resistant isolate of E. faecalis or a non-beta-lactamase-producing, aminoglycoside-susceptible isolate, and the mean log10 CFU per gram of vegetation were determined. The most active agents were low-dose ampicillin-sulbactam (200 mg/kg of body weight per day), high-dose ampicillin-sulbactam (400 mg/kg of body weight per day), and vancomycin (150 mg/kg of body weight per day), which reduced the titers of bacteria by 2.27, 2.76, and 2.85 log10 (CFU/g, respectively, compared with controls. While ampicillin-sulbactam and vancomycin were equally efficacious in reducing titers of bacteria in vegetations, no animals were cured (defined as < 2 log10 CFU/g of vegetation) by either agent, whether treatment was continued for 3 or 7 days. The addition of gentamicin was not associated with increased killing in rabbits infected with the aminoglycoside-resistant isolate. Both high-dose ampicillin-sulbactam and vancomycin regimens demonstrated significant, continued reduction in bacterial titers with the longer periods of treatment (P < or = 0.05); 7-day treatment with high-dose ampicillin-sulbactam produced a greater reduction in bacterial titers in vegetation than 7-day treatment with vancomycin (P < or = 0.05). We conclude that ampicillin-sulbactam and vancomycin are equally effective in the treatment of experimental endocarditis due to beta-lactamase-producing, highly gentamicin-resistant E. faecalis. The optimum therapy for such infections in humans is not known.
Quinolones potentiate cefazolin-induced seizures in DBA/2 mice
Authors: De Sarro A , Zappalá M , Chimirri A , Grasso S , De Sarro G B
Published: June 2012

The behavioral and convulsant effects of cefazolin, a beta-lactam derivative, were studied after intraperitoneal administration to DBA/2 mice, a strain genetically susceptible to sound-induced seizures, and Swiss mice. DBA/2 mice were more susceptible to seizures induced by cefazolin than were Swiss mice. The proconvulsant effects of some quinolones on seizures evoked by intraperitoneal administration of cefazolin were also evaluated in DBA/2 mice. Our study also demonstrated that the order of proconvulsant activity in our epileptic model was pefloxacin > enoxacin > ofloxacin > rufloxacin > norfloxacin > cinoxacin > ciprofloxacin > nalidixic acid. The relationships between the chemical structures and proconvulsant activities of quinolone derivatives were studied. The relationship between lipophilicity and proconvulsant activity was also investigated.