Three-dimensional chemical imaging of embedded nanoparticles using atom probe tomography.

Analysis of nanoparticles is often challenging especially when they are embedded in a matrix. Hence, we have used laser-assisted atom probe tomography (APT) to analyze the Au nanoclusters synthesized in situ using ion-beam implantation in a single crystal MgO matrix. APT analysis along with scanning transmission electron microscopy and energy dispersive spectroscopy (STEM-EDX) indicated that the nanoparticles have an average size ~8-12 nm. While it is difficult to analyze the composition of individual nanoparticles using STEM, APT analysis can give three-dimensional compositions of the same. It was shown that the maximum Au concentration in the nanoparticles increases with increasing particle size, with a maximum Au concentration of up to 50%.

In vitro antimicrobial activity of the novel polymeric guanidine Akacid plus.

The bactericidal and fungicidal activity of Akacid plus, a novel polymeric compound of the cationic family of disinfectants, was compared with chlorhexidine digluconate using quality control strains of Staphylococcus aureus, Enterococcus hirae, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. In vitro activity was determined using the quantitative suspension tests described by the European Committee for Standardization. These use concentrations of 0.01-0.5% against bacterial strains/C. albicans, with 0.5-4% against A. niger, and exposure times of 5, 15 and 60 min in the presence and absence of 0.3% bovine albumin and with dilution in distilled and hard water. In the basic quantitative suspension test, Akacid plus destroyed all bacterial pathogens at a concentration of 0.1% in < or =5 min. Chlorhexidine was also highly active against S. aureus, E. coli and P. aeruginosa, but failed to eliminate E. hirae within 5 min. A high organic load reduced the bactericidal activity of both disinfectants slightly. Akacid plus showed fungicidal activity against C. albicans within 15-60 min and eliminated A. niger at a concentration of 1% in 5 min of contact. Chlorhexidine was fungicidal against C. albicans, but not against A. niger.

Efficacy of macrolides vs. metronidazole against Entamoeba histolytica clinical isolates.

Current treatment of Entamoeba histolytica infection requires the use of several agents that are effective at different sites of the body. Commonly administered agents such as nitroimidazoles have a high rate of gastrointestinal side effects and their use is restricted during pregnancy. In order to offer new choices, four macrolide antibiotics (erythromycin, clarithromycin, azithromycin, josamycin) and metronidazole were tested for their in vitro activity against E. histolytica. Ten clinically isolated strains from an endemic area (Santo Domingo, Dominican Republic) were tested after polyxenical culture. Protozoan viability was significantly reduced by josamycin after 24 and 48 hours of incubation at a concentration of > or = 50 mg/l, which was slightly higher than that of metronidazole (25 mg/l). No resistance to metronidazole was found. The antiamebic activity of azithromycin, clarithromycin and erythromycin was significant at drug concentrations > or = 100 mg/l. High doses of josamycin, which is a very well tolerated drug, may serve as a useful therapeutic agent in the presence of E. histolytica infection.

Efficacy of beta-lactam and inhibitor combinations in a diffusion chamber model in rabbits.

Using a diffusion chamber in rabbits, we evaluated therapy with the combination of ceftriaxone plus the beta-lactamase inhibitor tazobactam in comparison with ceftriaxone alone. One sensitive and one resistant strain of Escherichia coli, Enterobacter cloacae and Klebsiella pneumoniae were inoculated into one of the six diffusion chambers, implanted in the same animal. In order to simulate pharmacokinetics in humans, both substances were administered in decreasing doses. Ceftriaxone was given 0, 2, 4 and 6 h after infection in dosages of 45, 35, 25 and 15 mg/kg of body weight, while tazobactam was administered either in one dose at 0 h, or divided into two doses at 0 and 1 h or 0 and 4 h, or divided into three doses at 0, 1 and 4 h after infection. The ratio of ceftriaxone:tazobactam was fixed at 8:1. Ceftriaxone, in combination with tazobactam, given in one dose immediately after infection showed a significant reduction in bacterial count. All other combinations of ceftriaxone and tazobactam did not differ from ceftriaxone in monotherapy. Co-administration of the beta-lactamase inhibitor tazobactam significantly enhanced the activity of ceftriaxone against all three tested species.

Comparative susceptibility to penicillin and quinolones of 1385 Streptococcus pneumoniae isolates. Austrian Bacterial Surveillance Network.

Antibiotic resistance among Streptococcus pneumoniae isolates has spread rapidly throughout the world since the first description of a strain with diminished susceptibility to penicillin in Australia in 1967. A total of 1385 strains of S. pneumoniae, collected in several centres throughout Austria, were assessed for their sensitivity to moxifloxacin, trovafloxacin, ciprofloxacin, ofloxacin, levofloxacin and lomefloxacin. The MICs were determined using the agar dilution method, according to NCCLS guidelines. Both moxlfloxacin and trovafloxacin showed good anti-pneumococcal activity in terms of MIC50 (both 0.125 mg/L) and MIC90 (both 0.25 mg/L). Less active, but with similar activity to each other, were ciprofloxacin and levofloxacin, each with an MIC50 of 1 mg/L and an MIC90 of 2 mg/L. Ofloxacin showed only moderate activity (MIC50, 1 mg/L; MIC90, 2 mg/L) and lomefloxacin was the least active compound (MIC50, 4 mg/L; MIC90, 8 mg/L). Both moxifloxacin and trovafloxacin at a concentration of < or = 0.5 mg/L inhibited all of the S. pneumoniae strains tested.

Effects of imipenem and meropenem on purine content of endothelial cells.

UNLABELLED: Intravenous compatibility of antibacterial agents has been tested in animal models. Use of human umbilical venous endothelial cells (HUVEC) to test antibiotic solutions for intravenous tolerance provides a valuable alternate model. OBJECTIVE: Evaluation of the effect of imipenem and meropenem on intracellular purines reflecting viability, energy production, signal transduction, and DNA/RNA synthesis of these cells. MATERIALS AND METHODS: Levels of intracellular adenosine 5' triphosphate (ATP), adenosine 5' diphosphate (ADP), guanosine 5' triphosphate (GTP) and guanosine 5' diphosphate (GDP) were measured by means of high performance liquid chromatography (HPLC). RESULTS: The total amount of ATP after incubation of cells with 10.0 mg/ml imipenem and meropenem for 20 minutes (12.93 +/- 0.93 nmol/million cells and 13.27 +/- 0.89 nmol/million cells, respectively) did not result in a decrease compared to controls (12.34 +/- 0.87 nmol/million cells). In addition, ATP levels were maintained or actually increased after 60 minutes. Incubation of cells with 5.0 mg/ml and 2.5 mg/ml of imipenem or meropenem for 20 and 60 minutes showed similar results. Purine nucleotide profiles of ADP, GTP, GDP following exposure of 10.0 mg/ml, 5.0 mg/ml and 2.5 mg/ml of imipenem and meropenem did not differ markedly. CONCLUSIONS: These in vitro data show an excellent endothelial compatibility of imipenem and meropenem even in high concentrations.

Fatal complication of paraffin plombage after half a century.

Complications following thoracic plombage for treatment of tuberculosis can be observed more than 50 years after placement of the filling. The management of these late complications is challenging and frequently requires surgical intervention. We report a patient who received a plombage in 1947. She was admitted to hospital with subfebrile temperature and hoarseness. A computed tomography scan of the chest revealed transthoracic penetration of the paraffin plombage with intrusion into the overlying soft tissue. The patient underwent excision and debridement of the paraffin wax mass followed by thoracoplasty. She then developed septicaemia and died due to multiple organ failure 23 days after the surgical intervention. Early ablation of plombage should be considered in order to prevent late complications.

Austrian national survey of prevalence of antimicrobial resistance among clinical isolates of Streptococcus pneumoniae 1994-96.

The antimicrobial susceptibilities of 1385 clinical isolates of Streptococcus pneumoniae obtained from 25 laboratories across Austria between December 1994 and January 1996 were tested. Minimal inhibitory concentration (MIC) values were determined in tests with penicillin, amoxycillin, amoxycillin/clavulanate, ceftriaxone, cefodizime, cefpirome, cefotaxime, cefpodoxime, cefadroxile, azithromycin, clarithromycin, josamycin and roxithromycin by the agar-dilution method. A total of 40 isolates (2.9%) demonstrated intermediate resistance (MIC 0.125-1 microg/ml) and 28 isolates (2.0%) had high-level resistance (MIC > or = 2 microg/ml) to penicillin. Excepting cefadroxil, with an MIC90 of 2 microg/ml, all other tested beta-lactams had MIC90s of 0.03-0.06 microg/ml. Penicillin-resistant strains were much more likely to be also resistant to the other beta-lactams. The macrolides proved to be very active compounds against pneumococci with MIC90s of 0.06 microg/ml (clarithromycin) and 0.25 microg/ml (all other macrolides). Regional differences within Austria with regard to antimicrobial resistance were not observed.

Bacterial growth in human vitreous humor.

The aim of this study was to investigate the capacity of human vitreous to support bacterial growth and to show differences in the growth kinetics of gram-positive and gram-negative bacteria. Vitreous gel of 70 keratoplasty donor eyes was sampled under sterile conditions, screened microscopically for cellular components and tested for sterility and levels of antibiotic drugs by bio-assay. The samples were inoculated with clinical isolates of Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus viridans and Streptococcus pyogenes. As control each strain was added both to 0.9% sodium chloride solution and to Mueller-Hinton broth. In order to determine bacterial growth the number of colony forming units was determined 4, 6, 24, 48 and 72 hr after inoculation by viable count. Vitreous gel did not support bacterial growth; the tested strains could not be recovered after 48 hr. Similar results could be obtained with sodium chloride; whereas in Mueller Hinton broth the strains showed normal pattern of growth. It seems that vitreous humor has inherent antibacterial capacity in vitro, although the responsible factors remain unknown.

Postantibiotic effect of ceftriaxone and gentamicin alone and in combination on Klebsiella pneumoniae, Pseudomonas aeruginosa and Streptococcus viridans.

A persistent suppression of bacterial growth following limited exposure to an antimicrobial agent, the postantibiotic effect (PAE), has been described for a variety of antibiotics and microorganisms. In this study the PAE of ceftriaxone and gentamicin was determined in vitro on three strains each of Klebsiella pneumoniae, Pseudomonas aeruginosa and Streptococcus viridans. The strains were exposed to the substances for 2 h at varying concentrations. Ceftriaxone was used at the minimal inhibitory concentration (MIC) and 1/2 MIC and gentamicin at 1/2 MIC, 1/4 MIC, and 1/8 MIC, each alone and in combination. Antibiotic concentrations were reduced by 1,000-fold dilution, bacterial regrowth was consequently monitored by viable count. The PAE of ceftriaxone alone reached up to 145 min (MIC) and 50 min (1/2 MIC), that of gentamicin alone up to 170 min (1/2 MIC), 135 min (1/4 MIC) and 70 min (1/8 MIC), depending on the bacterial species. Combinations of the antibiotics produced longer PAEs than one substance alone; the longest PAE was produced by the combination of ceftriaxone (MIC) and gentamicin (1/2 MIC) lasting up to 320 min (S. viridans). It may be important to take the PAE into account when evaluating dosing intervals.

Application of microdialysis to clinical pharmacokinetics in humans.

OBJECTIVE: Measurement of drug concentrations in tissues would be useful for clinical pharmacokinetic studies, but appropriate experimental methods are not available at present. The aim of this study was to assess the scope and limitations of the microdialysis technique for human tissue pharmacokinetic studies. METHODS: Microdialysis probes were inserted into the medial vastus muscle or the periumbilical subcutaneous adipose layer of 13 healthy volunteers. Thereafter, volunteers received either acetaminophen (paracetamol, 1000 mg orally) or gentamicin (160 mg, intravenous bolus). Drug concentrations were monitored in plasma, muscle, and subcutaneous tissue. Calibration of the microdialysis probes was carried out in vitro and in vivo with use of the retrodialysis method. RESULTS: For both model compounds, complete concentration versus time profiles in muscle and subcutaneous tissue could be obtained. Major pharmacokinetic parameters (absorption half-life, elimination half-life, maximum concentration, time to reach maximum concentration, area under the curve, and area under the inhibitory curve) were calculated for tissues; tissue/plasma concentration ratios could be derived. Reproducibility of tissue drug concentration measurements was high. CONCLUSIONS: We have shown that microdialysis sampling is a suitable tool for measuring drug concentrations in human muscle and subcutaneous tissues. Microdialysis is readily applicable, relatively noninvasive, and reproducible. This technique may become a valuable addition for pharmacokinetic characterization of selected drugs.