Structural Properties of the Caenorhabditis elegans Neuronal Network

Despite recent interest in reconstructing neuronal networks, complete wiring diagrams on the level of individual synapses remain scarce and the insights into function they can provide remain unclear. Even for Caenorhabditis elegans, whose neuronal network is relatively small and stereotypical from animal to animal, published wiring diagrams are neither accurate nor complete and self-consistent. Using materials from White et al. and new electron micrographs we assemble whole, self-consistent gap junction and chemical synapse networks of hermaphrodite C. elegans. We propose a method to visualize the wiring diagram, which reflects network signal flow. We calculate statistical and topological properties of the network, such as degree distributions, synaptic multiplicities, and small-world properties, that help in understanding network signal propagation. We identify neurons that may play central roles in information processing and network motifs that could serve as functional modules of the network. We explore propagation of neuronal activity in response to sensory or artificial stimulation using linear systems theory and find several activity patterns that could serve as substrates of previously described behaviors. Finally, we analyze the interaction between the gap junction and the chemical synapse networks. Since several statistical properties of the C. elegans network, such as multiplicity and motif distributions are similar to those found in mammalian neocortex, they likely point to general principles of neuronal networks. The wiring diagram reported here can help in understanding the mechanistic basis of behavior by generating predictions about future experiments involving genetic perturbations, laser ablations, or monitoring propagation of neuronal activity in response to stimulation

Implementation of a novel in vitro model of infection of reconstituted human epithelium for expression of virulence genes in methicillin-resistant Staphylococcus aureus strains isolated from catheter-related infections in Mexico

BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) are clinically relevant pathogens that cause severe catheter-related nosocomial infections driven by several virulence factors. METHODS: We implemented a novel model of infection in vitro of reconstituted human epithelium (RHE) to analyze the expression patterns of virulence genes in 21 MRSA strains isolated from catheter-related infections in Mexican patients undergoing haemodialysis. We also determined the phenotypic and genotypic co-occurrence of antibiotic- and disinfectant-resistance traits in the S. aureus strains, which were also analysed by pulsed-field-gel electrophoresis (PFGE). RESULTS: In this study, MRSA strains isolated from haemodialysis catheter-related infections expressed virulence markers that mediate adhesion to, and invasion of, RHE. The most frequent pattern of expression (present in 47.6% of the strains) was as follows: fnbA, fnbB, spa, clfA, clfB, cna, bbp, ebps, eap, sdrC, sdrD, sdrE, efb, icaA, and agr. Seventy-one percent of the strains harboured the antibiotic- and disinfectant-resistance genes ermA, ermB, tet(M), tet(K), blaZ, qacA, qacB, and qacC. PFGE of the isolated MRSA revealed three identical strains and two pairs of identical strains. The strains with identical PFGE patterns showed the same phenotypes and genotypes, including the same spa type (t895), suggesting hospital personnel manipulating the haemodialysis equipment could be the source of catheter contamination. CONCLUSION: These findings help define the prevalence of MRSA virulence factors in catheter-related infections. Some of the products of the expressed genes that we detected in this work may serve as potential antigens for inclusion in a vaccine for the prevention of MRSA-catheter-related infections

Two or more enteropathogens are associated with diarrhoea in Mexican children

<p>Abstract</p> <p>Background</p> <p>Diarrhoeal diseases constitute a major public health problem, particularly in the developing world, where the rate of mortality and morbidity is very high. The purpose of this study was to conduct a 2 years and 3 months study in order to determine the prevalence of five enteropathogen diarrheogenic agents in Mexico City.</p> <p>Methods</p> <p>Faecal samples were obtained from 300 Mexican children diagnosed as positive for diarrhoea, aged > 2 to < 12 years old, and from 80 children matched for age but with no symptoms of the disease (control group). Two multiplex PCR were used to detect <it>Escherichia coli</it>, <it>Salmonella </it>spp., and <it>Shigella </it>spp. In addition, the two protozoan parasites <it>Entamoeba histolytica/Entamoeba dispar </it>and <it>Giardia intestinalis </it>were detected by conventional methods.</p> <p>Results</p> <p>All diarrhoeal samples were positive for one or more enteropathogens. The most common enteropathogens in diarrhoeal samples were <it>E. histolytica/E. dispar </it>(70.3%), <it>Salmonella </it>(<it>ohio </it>28.3%; <it>typhimurium </it>16.3%; <it>infantis </it>8%; <it>anatum </it>0.6%; Newport 0.3%), <it>G. intestinalis </it>(33%), <it>E. coli </it>(ETEC 13.3%; EPEC 9.3%; VTEC 8.6%; EIEC 1%) and <it>Shigella </it>spp. (<it>flexneri </it>1.6%, <it>sonnei </it>1%). Infections by two (24%) three (16%) and four (12%) pathogens were observed.</p> <p>Conclusion</p> <p>This study revealed that 52% of the patients were infected by more than one enteropathogen, notably <it>E. histolitica</it>/<it>E. dispar </it>and <it>Salmonella ohio</it>. These results are useful for clinicians to improve the empiric treatment used in such cases.</p

Frequency of vacA, cagA and babA2 virulence markers in Helicobacter pylori strains isolated from Mexican patients with chronic gastritis

<p>Abstract</p> <p>Background</p> <p><it>Helicobacter pylori </it>has been strongly associated with chronic gastritis, peptic and duodenal ulcers, and it is a risk factor for gastric cancer. Three major virulence factors of <it>H. pylori </it>have been described: the vacuolating toxin (VacA), the cytotoxin-associated gene product (CagA) and the adhesion protein BabA2. Since considerable geographic diversity in the prevalence of <it>H. pylori </it>virulence factors has been reported, the aim of this work was to establish the <it>H. pylori </it>and <it>vacA</it>, <it>cagA </it>and <it>babA2 </it>gene status in 238 adult patients, from a marginal urban area of Mexico, with chronic gastritis.</p> <p>Methods</p> <p><it>H. pylori </it>was identified in cultures of gastric biopsies by nested PCR. <it>vacA </it>and <it>cagA </it>genes were detected by multiplex PCR, whereas babA2 gene was identified by conventional PCR.</p> <p>Results</p> <p><it>H. pylori</it>-positive biopsies were 143 (60.1%). All <it>H. pylori </it>strains were <it>vacA</it>⁺; 39.2% were <it>cagA</it>⁺; 13.3% were <it>cagA</it>⁺<it>babA2</it>⁺and 8.4% were <it>babA2</it>⁺. Mexican strains examined possessed the <it>vacA s1, m1 </it>(43.4%), <it>s1, m2 </it>(24.5%), <it>s2, m1 </it>(20.3%) and <it>s2, m2 </it>(11.9%) genotypes.</p> <p>Conclusion</p> <p>These results show that the Mexican patients suffering chronic gastritis we have studied had a high incidence of infection by <it>H. pylori</it>. Forty four percent (63/143) of the <it>H. pylori </it>strains analyzed in this work may be considered as highly virulent since they possessed two or three of the virulence markers analyzed: <it>vacA s1 cagA babA2 </it>(9.8%, 14/143), <it>vacA s1 babA2 </it>(4.9%, 7/143), and <it>vacA s1 cagA </it>(29.4%, 42/143). However, a statistically significant correlation was not observed between <it>vacAs1</it>, <it>cagA </it>and <it>babA2 </it>virulence markers (χ²test; P > 0.05).</p

Antibiotic and heavy metal resistance of Aeromonas hydrophila isolated from charal (Chirostoma humboldtianum, Valenciannes, 1835)

Antibiotic and heavy metal susceptibilities of twenty Aeromonas hydrophila strains, isolated from the gastrointestinal tract of the charal (Chirostoma humboldtianum), an autochthonous Mexican fish, were analyzed. All strains produced ?-lactamase and were resistant to penicillin and dicloxacillin, showing single peak for minimum inhibitory concentration (MIC) distributions at 2000-4000 µg/mL and 500-1000 µg/ml, respectively. Ampicillin MIC distribution was bimodal with 20% resistant strains (125-250 µg/ml) and 80% highly resistant ones (500-4000 µg/ml). All strains were susceptible to ceftriaxone (MIC= 3.9 µg/ml) and all but one were susceptible to cefuroxime (3.9 µg/ml and 62.5 µg/ml). All strains had a single MIC distribution pattern for lead (800-3200 µg/ml), and mercury (20 µg/ml) and were considered resistant and susceptible to these ions, respectively. Fifteen percent of the isolates were resistant to arsenite (MIC= 400-800 µg/ml) and all were susceptible to silver (MIC= 1.25-2.5µg/ml), chromate (MIC= 93.5-375 µg/ml), and zinc (MIC=21.25-42.5 µg/ml)

Asymmetric bias in user guided segmentations of brain structures

Brain morphometric studies often incorporate comparative hemispheric asymmetry analyses of segmented brain structures. In this work, we present evidence that common user guided structural segmentation techniques exhibit strong left-right asymmetric biases and thus fundamentally influence any left-right asymmetry analyses. In this study, MRI scans from ten pediatric subjects were employed for studying segmentations of amygdala, globus pallidus, putamen, caudate, and lateral ventricle. Additionally, two pediatric and three adult scans were used for studying hippocampus segmentation. Segmentations of the sub-cortical structures were performed by skilled raters using standard manual and semi-automated methods. The left-right mirrored versions of each image were included in the data and segmented in a random order to assess potential left-right asymmetric bias. Using shape analysis we further assessed whether the asymmetric bias is consistent across subjects and raters with the focus on the hippocampus

Preserving and Using Germplasm and Dissociated Embryonic Cells for Conserving Caribbean and Pacific Coral

Coral reefs are experiencing unprecedented degradation due to human activities, and protecting specific reef habitats may not stop this decline, because the most serious threats are global (i.e., climate change), not local. However, ex situ preservation practices can provide safeguards for coral reef conservation. Specifically, modern advances in cryobiology and genome banking could secure existing species and genetic diversity until genotypes can be introduced into rehabilitated habitats. We assessed the feasibility of recovering viable sperm and embryonic cells post-thaw from two coral species, Acropora palmata and Fungia scutaria that have diffferent evolutionary histories, ecological niches and reproductive strategies. In vitro fertilization (IVF) of conspecific eggs using fresh (control) spermatozoa revealed high levels of fertilization (>90% in A. palmata; >84% in F. scutaria; P>0.05) that were unaffected by tested sperm concentrations. A solution of 10% dimethyl sulfoxide (DMSO) at cooling rates of 20 to 30°C/min most successfully cryopreserved both A. palmata and F. scutaria spermatozoa and allowed producing developing larvae in vitro. IVF success under these conditions was 65% in A. palmata and 53% in F. scutaria on particular nights; however, on subsequent nights, the same process resulted in little or no IVF success. Thus, the window for optimal freezing of high quality spermatozoa was short (∼5 h for one night each spawning cycle). Additionally, cryopreserved F. scutaria embryonic cells had∼50% post-thaw viability as measured by intact membranes. Thus, despite some differences between species, coral spermatozoa and embryonic cells are viable after low temperature (−196°C) storage, preservation and thawing. Based on these results, we have begun systematically banking coral spermatozoa and embryonic cells on a large-scale as a support approach for preserving existing bio- and genetic diversity found in reef systems