Mode structure of coupled L3 photonic crystal cavities.

We investigate the energy splitting, quality factor and polarization of the fundamental modes of coupled L3 photonic crystal cavities. Four different geometries are evaluated theoretically, before experimentally investigating coupling in a direction at 30◦ to the line of the cavities. In this geometry, a smooth variation of the energy splitting with the cavity separation is predicted and observed, together with significant differences between the polarizations of the bonding and anti-bonding states. The controlled splitting of the coupled states is potentially useful for applications that require simultaneous resonant enhancement of two transitions.

Splitting and lasing of whispering gallery modes in quantum dot micropillars.

We have studied the whispering gallery mode (WGM) resonances of GaAs/AlGaAs microcavity pillars containing InAs quantum dots. High quality factor WGMs are observed from a wide range of pillars with diameters from 1.2 to 50 µm. Multimode lasing with sub-milliwatt thresholds and high beta-factors approaching unity is observed under optical pumping in a 4 µm diameter pillar. Mode splitting is observed in WGMs from pillars with diameters of 5 µm, 20 µm and 50 µm.We develop a model in which the mode splitting in the larger pillars is caused by resonant scattering from the quantum dots themselves. The model explains why splittings are observed in all of the larger pillars and that the splitting decreases with increasing wavelength. Numerical simulations by COMSOL confirm that the model is plausible. This mechanism of splitting should be general for all circular resonant structures containing quantum dots such as microdisks, rings, toroids, and microspheres.

Polarized quantum dot emission from photonic crystal nanocavities studied under moderesonant enhanced excitation.

We study the linear polarization of the emission from single quantum dots embedded in an "L3" defect nanocavity in a two-dimensional photonic crystal. By using narrow linewidth optical excitation in resonance with higher-order modes, we are able to achieve strong quantum dot emission intensity whilst reducing the background from quantum dots in the surrounding lattice. We find that all the dots observed emit very strongly linearly polarized light of the same orientation as the closest mode, despite the fact that these quantum dots may be spectrally detuned by several times the mode linewidth. We discuss the coupling mechanisms which may explain this behavior.

Early epithelial invasion by Salmonella enterica serovar Typhimurium DT104 in the swine ileum.

Salmonella enterica serovar Typhimurium is an important intestinal pathogen in swine. This study was performed to document the early cellular invasion of Salmonella serovar Typhimurium in swine ileum. Ileal gut-loops were surgically prepared in ten 4- to 5-week-old mixed-breed pigs and inoculated for 0-60 minutes. Loops were harvested and prepared for both scanning and transmission electron microscopy (SEM and TEM, respectively). Preferential bacterial adherence to microfold cells (M cells) was seen within 5 minutes, and by 10 minutes bacterial invasion of the apical membrane was seen in M cells, goblet cells, and enterocytes. This multicellular invasion was observed throughout the course of infection. In addition, SEM revealed a specific affinity of Salmonella serovar Typhimurium to sites of cell extrusion. Using TEM, bacteria in these areas were focused in the crevices formed by the extruding cell and the adjacent cells and in the cytoplasm immediately beneath the extruding cell. Our results suggest that early cellular invasion by Salmonella serovar Typhimurium is nonspecific and rapid in swine. Furthermore, the combination of SEM and TEM data suggests that Salmonella serovar Typhimurium may use sites of cell extrusion as an additional mechanism for early invasion.

Measurements of the cross section for e(+)e(-) --> hadrons at center-of-mass energies from 2 to 5 GeV.

We report values of R = sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->mu(+)mu(-)) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.

Hha is a negative modulator of transcription of hilA, the Salmonella enterica serovar Typhimurium invasion gene transcriptional activator.

An early step in the establishment of Salmonella enterica serovar Typhimurium murine infection is the penetration of the intestinal mucosa of the small intestine. The majority of the genes responsible for the Salmonella invasive phenotype are encoded on Salmonella pathogenicity island 1, and their transcription is controlled by the hilA transcriptional activator. The expression of hilA is regulated by environmental signals including oxygen, osmolarity, pH, and growth phase such that the presence of any one suboptimal condition results in repression of hilA expression and the invasive phenotype. We have conducted a search for negative regulators of hilA by introduction of a Salmonella enterica serovar Typhimurium chromosomal DNA gene bank into a Salmonella enterica serovar Typhimurium hilA::Tn5lacZY reporter strain. This screen has identified the hha gene as a regulator that exerts a negative influence on hilA expression. Plasmid-encoded hha significantly reduces hilA::Tn5lacZY chromosomal expression, as well as expression of the invasion genes invF, prgH, and sipC. An hha null mutation results in substantial derepression of both chromosomally encoded and plasmid-encoded hilA::Tn5lacZY expression. Introduction of plasmid-encoded hha into strain SL1344 results in attenuation of invasion using in vitro and in vivo assays. Importantly, purified Hha protein was found to bind to a hilA DNA promoter fragment, suggesting that the regulatory activity of the Hha protein occurs at the hilA promoter. These data add detail to the developing model of the regulation of Salmonella invasion genes.

Secretion of a putative cytotoxin in multiple antibiotic resistant Salmonella enterica serotype Typhimurium phagetype DT104.

Salmonella enterica serotype Typhimurium phagetype DT104 (DT104) is a multiple antibiotic-resistant pathogen. DT104 infections have been reported in a multitude of hosts including humans, companion animals, livestock and wildlife. Recently, several isolates of DT104 were recovered from veal calves exhibiting abomasitis, a finding that is inconsistent with classic salmonellosis. One of these isolates was used in murine ligated loop experiments where it was observed that multiresistant DT104 can elaborate a putative cytotoxin. Thus it appears that DT104 has the ability to evade pharmacologic interventions, via antibiotic resistance, and elaborate a toxin that can damage cells.

Identification of Listeria monocytogenes in vivo-induced genes by fluorescence-activated cell sorting.

Listeria monocytogenes is a gram-positive, intracellular, food-borne pathogen capable of causing severe infections in immunocompromised or pregnant individuals, as well as numerous animal species. Genetic analysis of Listeria pathogenesis has identified several genes which are crucial for virulence. The transcription of most of these genes has been shown to be induced upon entry of Listeria into the host cell. To identify additional genes that are induced in vivo and may be required for L. monocytogenes pathogenesis, a fluorescence-activated cell-sorting technique was initiated. Random fragments of the L. monocytogenes chromosome were cloned into a plasmid carrying a promoterless green fluorescent protein (GFP) gene, and the plasmids were transformed into the L. monocytogenes actA mutant DP-L1942. Fluorescence-activated cell sorting (FACS) was used to isolate L. monocytogenes clones that exhibited increased GFP expression within macrophage-like J774 cells but had relatively low levels of GFP expression when the bacteria were extracellular. Using this strategy, several genes were identified, including actA, that exhibited such an expression profile. In-frame deletions of two of these genes, one encoding the putative L. monocytogenes uracil DNA glycosylase (ung) and one encoding a protein with homology to the Bacillus subtilis YhdP hemolysin-like protein, were constructed and introduced into the chromosome of wild-type L. monocytogenes 10403s. The L. monocytogenes 10403s ung deletion mutant was not attenuated for virulence in mice, while the yhdP mutant exhibited a three- to sevenfold reduction in virulence.

Salmonella pathogenicity island 2-encoded type III secretion system mediates exclusion of NADPH oxidase assembly from the phagosomal membrane.

Salmonella typhimurium requires a type III secretion system encoded by pathogenicity island (SPI)-2 to survive and proliferate within macrophages. This survival implies that S. typhimurium avoids or withstands bactericidal events targeted to the microbe-containing vacuole, which include intraphagosomal production of reactive oxygen species (ROS), phagosomal acidification, and delivery of hydrolytic enzymes to the phagosome via fusion with lysosomes. Recent evidence suggests that S. typhimurium alters ROS production by murine macrophages in an SPI-2-dependent manner. To gain insights into the mechanism by which S. typhimurium inhibits intraphagosomal ROS production, we analyzed the subcellular distribution of NADPH oxidase components during infection of human monocyte-derived macrophages by wild-type (WT) or several SPI-2 mutant strains of S. typhimurium. We found that the membrane component of the NADPH oxidase, flavocytochrome b(558), was actively excluded or rapidly removed from the phagosomal membrane of WT-infected monocyte-derived macrophages, thereby preventing assembly of the NADPH oxidase complex and intraphagosomal production of superoxide anion. In contrast, the NADPH oxidase assembled on and generated ROS in phagosomes containing SPI-2 mutant S. typhimurium. Subversion of NADPH oxidase assembly by S. typhimurium was accompanied by increased bacterial replication relative to that of SPI-2 mutant strains, suggesting that the ability of WT S. typhimurium to prevent NADPH oxidase assembly at the phagosomal membrane represents an important virulence factor influencing its intracellular survival.

A set of ftsZ mutants blocked at different stages of cell division in Caulobacter.

FtsZ is required throughout the cell division process in eubacteria and in archaea. We report the isolation of novel mutants of the FtsZ gene in Caulobacter crescentus. Clusters of charged amino acids were changed to alanine to minimize mutations that affect protein folding. Molecular modelling indicated that all the clustered-charged-to-alanine mutations had altered amino acids at the surface of the protein. Of 13 such mutants, four were recessive-lethal, three were dominant-lethal, and six had no discernible phenotype. An FtsZ depletion strain of Caulobacter was constructed to analyse the phenotype of the recessive-lethal mutations and used to show that they blocked cell division at distinct stages. One mutation blocked the initiation of cell division, two mutations blocked cell division randomly, and one mutation blocked both early and late stages of cell division. The effect of the recessive mutations on the subcellular localization of FtsZ was determined. Models to explain the various mutant phenotypes are discussed. This is the first set of recessive alleles of ftsZ blocked at different stages of cell division.

Salmonella pathogenicity island 2-encoded proteins SseC and SseD are essential for virulence and are substrates of the type III secretion system.

Survival of Salmonella enterica serovar Typhimurium within host phagocytic cells is a critical step in establishing systemic infection in mice. Genes within Salmonella pathogenicity island 2 (SPI-2) encode a type III secretion system that is required for establishment of systemic infection. Several proteins encoded by SPI-2 have homology to type III secreted proteins from enteropathogenic Escherichia coli and Yersinia and, based on that homology, are predicted to be secreted through the SPI-2 type III secretion system. We have investigated the roles of two of these proteins, SseC and SseD. We demonstrate here that the SseD protein is required for systemic Salmonella infection of the mouse, and we confirmed the virulence requirement for the SseC protein. Experiments were performed, using cellular fractionation and immunoblotting, to identify the subcellular location of the SseC and SseD proteins. Both proteins were found to localize predominantly to the bacterial cell membrane. In addition, our work revealed that SseC and SseD are exposed to the extracellular environment and are loosely associated with the bacterial membrane. Furthermore, localization of SseC and SseD to the bacterial membrane was found to require a functional SPI-2 type III secretion system. Collectively, these results indicate that the SseC and SseD proteins are secreted by the SPI-2 type III secretion system to the bacterial membrane in order to perform their virulence functions.

Evaluation of immobilized redox indicators as reversible, in situ redox sensors for determining Fe(III)-reducing conditions in environmental samples.

An in situ methodology based on immobilized redox indicators has been developed to determine when Fe(III)-reducing conditions exist in environmental systems. The redox indicators thionine (Thi, formal potential at pH 7 (E(7)(0')) equals 66 mV), toluidine blue O (TB, E(7)(0')=31 mV), and cresyl violet (CV, E(7)(0')=-75 mV) have been immobilized to 40-60 mum agarose beads via an amine-aldehyde coupling reaction. These beads were packed into a flow cell to allow spectrophotometric monitoring of the redox state of simple solutions and wastewater slurries pumped from in a bioreactor. Fe(II), a product of microbial activity, at levels observed in real systems reduces both the free (non-immobilized) and immobilized redox indicator to different degrees for samples with pH 6.5 or higher. At pH 7, immobilized Thi and TB are significantly reduced at Fe(II) concentrations greater than 0.1 and 0.3 mM, respectively. CV, with the lowest formal potential, requires Fe(II) levels in excess of 10 mM. The degree of reduction of the indicators (i.e. the fraction of indicator oxidized) observed during titrations can be qualitatively modeled with a simple equilibrium model based on ferrihydrite or lepidocrocite as the Fe(III)-solid phase. The reversibility of Fe(II)-indicator reactions was also demonstrated by showing that the reduced indicator becomes re-oxidized when Fe(II) levels decrease.

Fis, a DNA nucleoid-associated protein, is involved in Salmonella typhimurium SPI-1 invasion gene expression.

The ability of Salmonella enterica serovar Typhimurium to cause disease depends upon the co-ordinated expression of many genes located around the Salmonella chromosome. Specific pathogenicity loci, termed Salmonella pathogenicity islands, have been shown to be crucial for the invasion and survival of Salmonella within host cells. Salmonella pathogenicity island 1 (SPI-1) harbours the genes required for the stimulation of Salmonella uptake across the intestinal epithelia of the infected host. Regulation of SPI-1 genes is complex, as invasion gene expression responds to a number of different signals, presumably signals similar to those found within the environment of the intestinal tract. As a result of our continued studies of SPI-1 gene regulation, we have discovered that the nucleoid-binding protein Fis plays a pivotal role in the expression of HilA and InvF, two activators of SPI-1 genes. A S. typhimurium fis mutant demonstrates a two- to threefold reduction in hilA:Tn5lacZY and a 10-fold reduction in invF:Tn5lacZY expression, as well as a 50-fold decreased ability to invade HEp-2 tissue culture cells. This decreased expression of hilA and invF resulted in an altered secreted invasion protein profile in the fis mutant. Furthermore, the virulence of a S. typhimurium fis mutant is attenuated 100-fold when administered orally, but has wild-type virulence when administered intraperitoneally. Expression of hilA:Tn5lacZY and invF:Tn5lacZY in the fis mutant could be restored by introducing a plasmid containing the S. typhimurium fis gene or a plasmid containing hilD, a gene encoding an AraC-like regulator of Salmonella invasion genes.

Salmonella enterica serovars gallinarum and pullorum expressing Salmonella enterica serovar typhimurium type 1 fimbriae exhibit increased invasiveness for mammalian cells.

Salmonella enterica serovars Gallinarum and Pullorum are S. enterica biotypes that exhibit host specificity for poultry and aquatic birds and are not normally capable of causing disease in mammalian hosts. During their evolution toward host restriction serovars Gallinarum and Pullorum lost their ability to mediate mannose-sensitive hemagglutination (MSHA), a phenotype correlated with adherence to certain cell types. Because adherence is an essential requirement for invasion of cells by bacterial pathogens, we examined whether MHSA type 1 fimbriae would increase the ability of serovars Pullorum and Gallinarum to invade normally restrictive cells. Serovars Gallinarum and Pullorum expressing S. enterica serovar Typhimurium strain LT2 type 1 fimbriae exhibited a 10- to 20-fold increased ability to adhere to and a 20- to 60-fold increased invasion efficiency of the human epithelial HEp-2 cell line. Invasion was accompanied by extensive ruffling of the membranes of the HEp-2 cells. In a murine ligated ileal loop model, a 32% increase in the number of M-cell ruffles was seen when serovar Gallinarum expressed serovar Typhimurium type 1 fimbriae.

Transcriptional organization and function of invasion genes within Salmonella enterica serovar Typhimurium pathogenicity island 1, including the prgH, prgI, prgJ, prgK, orgA, orgB, and orgC genes.

Salmonella enterica serovar Typhimurium initiates infection of a host by inducing its own uptake into specialized M cells which reside within the epithelium overlaying Peyer's patches. Entry of Salmonella into intestinal epithelial cells is dependent upon invasion genes that are clustered together in Salmonella pathogenicity island 1 (SPI-1). Upon contact between serovar Typhimurium and epithelial cells targeted for bacterial internalization, bacterial proteins are injected into the host cell through a type III secretion system that leads to internalization of the bacteria. Previous work has established that the prgH, -I, -J, and -K and orgA genes reside in SPI-1, and the products of these genes are predicted to be components of the invasion secretion apparatus. We report that an error in the published orgA DNA sequence has been identified so that this region encodes two small genes rather than a single large open reading frame. These genes have been designated orgA and orgB. Additionally, an opening reading frame downstream of orgB, which we have designated orgC, has been identified and partially characterized. Previously published work has indicated that the prgH, -I, -J, and -K genes are transcribed from a promoter distinct from that used by the gene immediately downstream, orgA. Here, we present experiments indicating that orgA expression is driven by the prgH promoter. In addition, using reverse transcriptase PCR analysis, we have found that this polycistronic message extends downstream of prgH to include a total of 10 genes. To more fully characterize this invasion operon, we demonstrate that the prgH, prgI, prgJ, prgK, orgA, and orgB genes are each required for invasion and secretion, while orgC is not essential for the invasive phenotype.

Identification and characterization of mutants with increased expression of hilA, the invasion gene transcriptional activator of Salmonella typhimurium.

Induction of invasion gene transcription and expression of the invasive phenotype of Salmonella strains are regulated by environmental conditions. Experimental evidence indicates that oxygen, pH, and osmotic conditions need to closely resemble those of the host intestinal lumen for invasion gene activation. The hilA gene, encoded on Salmonella pathogenicity island 1 (SPI-1), is a transcriptional activator which is required for invasion and whose expression is modulated by oxygen, pH, and osmolarity. Additionally, hilA is regulated by genetic elements encoded on SPI-1 (hilC/sirC/sprA and hilD), as well as by elements which reside outside of SPI-1 (phoP/phoQ and sirA), although how environmental signals modulate hilA is unknown. In an effort to further characterize the Salmonella invasion gene regulon, we have created and preliminarily characterized 18 Tn5 insertions which result in upregulation of a hilA::lacZY fusion. We have classified the mutations based on location and phenotype into three classes. Six class 1 and six class 2 mutants have insertions in SPI-1 near the invasion gene orgA or the invasion gene regulator hilD, respectively. Six class 3 mutants reside outside of SPI-1 in four different loci. The class 2 and 3 mutations induce overexpression of an episomal hilA::lacZY fusion and significantly increase S. typhimurium invasion of HEp-2 cells in a standard invasion assay. These data implicate new regions of SPI-1 as being involved in the regulation of invasion by S. typhimurium and identify new invasion gene regulators located outside of SPI-1.

Neuropsychological change in early phase schizophrenia during 12 months of treatment with olanzapine, risperidone, or haloperidol. The Canadian Collaborative Group for research in schizophrenia.

BACKGROUND: The purpose of this investigation was to test the efficacy of novel antipsychotic medications in the treatment of cognitive impairment in early phase schizophrenia. METHODS: Sixty-five patients in this multicenter double-blind study were randomly assigned to olanzapine (5-20 mg), risperidone (4-10 mg), or haloperidol (5-20 mg). Standard measures of clinical and motor syndromes were administered, as well as a comprehensive battery of tests to assess (1) motor skills, (2) attention span, (3) verbal fluency and reasoning, (4) nonverbal fluency and construction, (5) executive skills, and (6) immediate recall at baseline and after 6, 30, and 54 weeks of treatment. RESULTS: The general cognitive index derived from the 6 domain scores revealed a significantly greater benefit from treatment with olanzapine relative to haloperidol and olanzapine relative to risperidone, but no significant difference was shown between risperidone and haloperidol. The improvement related to olanzapine was apparent after 6 weeks and enhanced after 30 and 54 weeks of treatment. Exploratory within-group analyses of the 6 cognitive domains after a conservative Bonferroni adjustment revealed a significant improvement with olanzapine only on the immediate recall domain, and similar analyses of the 17 individual tests revealed a significant improvement with olanzapine only on the Hooper Visual Organization Test. CONCLUSIONS: These data suggest that olanzapine has some superior cognitive benefits relative to haloperidol and risperidone. A larger sample replication study is necessary to confirm and generalize the observations of this study and begin evaluation of the implications of this change to cerebral function and quality of life for people with schizophrenia.

Identification of diminished tissue culture invasiveness among multiple antibiotic resistant Salmonella typhimurium DT104.

Salmonella infections continue to cause gastrointestinal and systemic disease throughout the world. Salmonella typhimurium further poses a major health concern due to its apparent enhanced ability to acquire multiple antibiotic resistance genes. Currently it is unclear if multiresistant S. typhimurium are more or less pathogenic than non-resistant counterparts. Using an in vitro invasion assay, we evaluated the relative pathogenicity of over 400 multiresistant S. typhimurium isolates. Our studies failed to identify any <<<>>> isolates. However, we identified 12 isolates exhibiting invasive phenotypes that were constrained relative to controls. These <<<>>> strains were found in a variety of phagetypes all possessing at least a hexaresistant profile. Further studies revealed that the alterations in invasion were not due to changes in adherence. Limited studies exploring in vivo virulence revealed a mildly decreased ability to cause murine lethality for the hypoinvasive strain examined. These results indicate that the ability to cause disease is not increased but is rather mildly attenuated for certain isolates of multiresistant S. typhimurium.

Clinical evaluation of a modified circumcostal gastropexy in dogs.

A modified circumcostal gastropexy was performed in 5 Greyhounds. A 3-cm-long tunnel was created between the seromuscular and submuscosal layers of the pyloric antrum. A 6- to 7-cm-long segment of the cartilaginous portion of the 10th or 11th rib was dissected free of surrounding tissues and transected; the proximal portion of the rib was inserted through the seromuscular tunnel. The transected ends of the rib were overlapped approximately 1.5 cm and sutured in apposition in a side-by-side manner. Mean time for completion of the gastropexy was 11.5 minutes. Persistence of the surgically created gastric adhesion was verified by laparoscopy and ultrasonography 6 and 18 months after surgery. Positive-contrast radiography confirmed normal anatomic position of the stomach. Important complications associated with the procedure were not detected. Results for these 5 dogs indicated that modified circumcostal gastropexy could be performed rapidly, was safe, and created long-lasting gastric fixation.

Simultaneous chemotherapy and radiotherapy with escalating doses of chemotherapy in patients with advanced esophageal carcinoma.

From January 1992 to January 1995, 39 patients were diagnosed with esophageal carcinoma at the Department of Veterans Affairs Medical Center in Washington, D.C. All of the patients were men aged 44 to 78, and the median age was 66. Staging included a physical examination, serum chemistries, barium swallow, endoscopy with biopsy, and computed tomographic scans of the chest and abdomen. Seven patients were ineligible for the study because they had poor performance status, refused treatment, or received treatment at another medical center. All the patients treated had a performance status of 1 to 2. In 1992, 15 patients received 400 mg/m2/d 5-fluorouracil; in 1993, eight patients received 500 mg/m2/d 5-fluorouracil; and in 1994, nine patients received 600 mg/m2/d 5-fluorouracil as a continuous intravenous infusion during radiotherapy, which consisted of 60 Gy over 6 to 8 weeks. The complete response rates were 26%, 25%, and 22% for 1992, 1993, and 1994, respectively. The median survival was 11 months, 14 months and 9 months for those same years, respectively. The major toxicities were hematologic. Three patients died of pneumonia during treatment. Simultaneous chemotherapy and radiotherapy is an effective mode of therapy for localized esophageal carcinoma. However, escalating doses of chemotherapy did not increase the complete response rate.