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Haemophilus somnus Possesses Two Systems for Acquisition of Transferrin-Bound Iron. Andrew Ekins, 2004.Haemophilus somnus strain 649 was found to acquire iron from ovine, bovine, and goat transferrins (Tfs) . Expression of Tf receptors, as evaluated by solid-phase binding assays, required the organisms to be grown under iron-restricted conditions in the presence of Tf . Competition binding assays revealed the presence of two distinct Tf-binding receptor systems, one specific for bovine Tf and the other capable of binding all three ruminant Tfs . Affinity isolation procedures using total membranes yielded three putative bovine Tf-binding polypeptides and one putative ovine and goat Tf-binding polypeptide . PCR amplification followed by DNA sequence analyses revealed that H . somnus strain 649 possesses genes that encode a bipartite TbpA-TbpB receptor along with a homolog of the Histophilus ovis single-component TbpA receptor . Expression of TbpB and the single-component TbpA would appear to be subject to a form of phase variation involving homopolymeric nucleotide tracts within the structural genes . Ertapenem Pharmacokinetics and Impact on Intestinal Microflora, in Comparison to Those of Ceftriaxone, after Multiple Dosing in Male and Female Volunteers. Mathias W. R. Pletz, 2004.The pharmacokinetics of ertapenem and ceftriaxone were investigated in an open, randomized, two-period crossover study after single- and multiple-dose administration in 10 healthy volunteers (five women and five men) . Both antibiotics were administered intravenously once daily for 7 days at dosages of 1 g (ertapenem) and 2 g (ceftriaxone) . The concentrations of the antibiotics in serum and urine were quantified by the agar well diffusion method bioassay and, in addition, for ertapenem only, by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) . For ertapenem the maximum concentration of the drug in plasma (Cmax) was 256 mg/liter, the half-life was 20.7 h, and the area under the plasma concentration-time curve (AUC) was 830 mg · h/liter . The concentrations in fecal samples were (mean value) 37.2 and 32.7 mg/kg on day 4 and day 8, respectively . Ceftriaxone exhibited a mean Cmax of 315 mg/liter, a half-life of 7.6 h, and an AUC of 1,556 mg · h/liter . The mean concentrations in fecal samples were 153 and 258 mg/kg on day 4 and day 8, respectively . No accumulation of ertapenem or ceftriaxone was detected at steady state . A slightly but significantly decreased AUC for ertapenem was detected for the female volunteers . No serious adverse event was observed . Both antibiotics induced a marked decrease in the anaerobic microflora (4-log-unit decreases in lactobacilli, bifidobacteria, clostridia, and bacteroides) and Escherichia coli, whereas the number of enterococci increased (4 log units) . A slight overgrowth of yeasts was observed with both regimens . In all cases the microflora returned to normal levels on days 21 to 35 . Optimization of Single-Base-Pair Mismatch Discrimination in Oligonucleotide Microarrays. Hidetoshi Urakawa, 2003.The discrimination between perfect-match and single-base-pair-mismatched nucleic acid duplexes was investigated by using oligonucleotide DNA microarrays and nonequilibrium dissociation rates (melting profiles) . DNA and RNA versions of two synthetic targets corresponding to the 16S rRNA sequences of Staphylococcus epidermidis (38 nucleotides) and Nitrosomonas eutropha (39 nucleotides) were hybridized to perfect-match probes (18-mer and 19-mer) and to a set of probes having all possible single-base-pair mismatches . The melting profiles of all probe-target duplexes were determined in parallel by using an imposed temperature step gradient . We derived an optimum wash temperature for each probe and target by using a simple formula to calculate a discrimination index for each temperature of the step gradient . This optimum corresponded to the output of an independent analysis using a customized neural network program . These results together provide an experimental and analytical framework for optimizing mismatch discrimination among all probes on a DNA microarray .
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