Two Different rpf Clusters Distributed among a Population of Stenotrophomonas maltophilia Clinical Strains Display Differential Diffusible Signal Factor Production and Virulence Regulation

The quorum-sensing (QS) system present in the emerging nosocomial pathogen Stenotrophomonas maltophilia is based on the signaling molecule diffusible signal factor (DSF). Production and detection of DSF are governed by the rpf cluster, which encodes the synthase RpfF and the sensor RpfC, among other components. Despite a well-studied system, little is known about its implication in virulence regulation in S. maltophilia. Here, we have analyzed the rpfF gene from 82 S. maltophilia clinical isolates. Although rpfF was found to be present in all of the strains, it showed substantial variation, with two populations (rpfF-1 and rpfF-2) clearly distinguishable by the N-terminal region of the protein. Analysis of rpfC in seven complete genome sequences revealed a corresponding variability in the N-terminal transmembrane domain of its product, suggesting that each RpfF variant has an associated RpfC variant. We show that only RpfC–RpfF-1 variant strains display detectable DSF production. Heterologous rpfF complementation of ΔrpfF mutants of a representative strain of each variant suggests that RpfF-2 is, however, functional and that the observed DSF-deficient phenotype of RpfC–RpfF-2 variant strains is due to permanent repression of RpfF-2 by RpfC-2. This is corroborated by the ΔrpfC mutant of the RpfC–RpfF-2 representative strain. In line with this observations, deletion of rpfF from the RpfC–RpfF-1 strain leads to an increase in biofilm formation, a decrease in swarming motility, and relative attenuation in the Caenorhabditis elegans and zebrafish infection models, whereas deletion of the same gene from the representative RpfC–RpfF-2 strain has no significant effect on these virulence-related phenotypes.     

Trypanosoma vivax: mechanical transmission in cattle by one of the most common African tabanids,Atylotus agrestis

The role of mechanical vectors in the transmission of African livestock trypanosomes has always been controversial relative to tsetse flies, their cyclical vectors. An experiment was carried out in Burkina Faso to demonstrate mechanical transmission of Trypanosoma vivax by one of the most common tabanids in Africa: Atylotus agrestis. Eight heifers (crossbred zebuxBaoulé), free of trypanosome infection, were kept in a corral covered by a mosquito net, together with two heifers infected experimentally with a local stock of T. vivax. On average, 324 A. agrestis, freshly captured with Nzi traps, were introduced daily over 20 days. Parasitological, PCR and serological examinations were carried out regularly to assess infections and levels of parasitaemia. Microscopic examination of buffy-coats indicated that five of the eight receiver-heifers were infected on days 8, 13, 32, 41, and 48. PCR results indicated that these five heifers were already infected by day 13. Mechanical transmission of T. vivax by A. agrestis was demonstrated unequivocally, at a high rate (63% in 13-20 days). Conditions of transmission in this experiment are discussed in terms of natural rates of challenge. The importance of tabanids as mechanical vectors of T. vivax should be re-considered, in light of these results. Creation of tsetse free zones in Africa will generally lead to the disappearance of T. congolense, T. brucei, and most often T. vivax as well; however, in areas where T. vivax can be mechanically transmitted, clearance of tsetse may not be sufficient to eradicate livestock trypanosomosis.     

Filariasis Attenuates Anemia and Proinflammatory Responses Associated with Clinical Malaria: A Matched Prospective Study in Children and Young Adults

Background

Wuchereria bancrofti (Wb) and Mansonella perstans (Mp) are blood-borne filarial parasites that are endemic in many countries of Africa, including Mali. The geographic distribution of Wb and Mp overlaps considerably with that of malaria, and coinfection is common. Although chronic filarial infection has been shown to alter immune responses to malaria parasites, its effect on clinical and immunologic responses in acute malaria is unknown.

Methodology/Principal Findings

To address this question, 31 filaria-positive (FIL+) and 31 filaria-negative (FIL−) children and young adults, matched for age, gender and hemoglobin type, were followed prospectively through a malaria transmission season. Filarial infection was defined by the presence of Wb or Mp microfilariae on calibrated thick smears performed between 10 pm and 2 am and/or by the presence of circulating filarial antigen in serum. Clinical malaria was defined as axillary temperature ≥37.5°C or another symptom or sign compatible with malaria infection plus the presence of asexual malaria parasites on a thick blood smear. Although the incidence of clinical malaria, time to first episode, clinical signs and symptoms, and malaria parasitemia were comparable between the two groups, geometric mean hemoglobin levels were significantly decreased in FIL− subjects at the height of the transmission season compared to FIL+ subjects (11.4 g/dL vs. 12.5 g/dL, p<0.01). Plasma levels of IL-1ra, IP-10 and IL-8 were significantly decreased in FIL+ subjects at the time of presentation with clinical malaria (99, 2145 and 49 pg/ml, respectively as compared to 474, 5522 and 247 pg/ml in FIL− subjects).

Conclusions/Significance

These data suggest that pre-existent filarial infection attenuates immune responses associated with severe malaria and protects against anemia, but has little effect on susceptibility to or severity of acute malaria infection. The apparent protective effect of filarial infection against anemia is intriguing and warrants further study in a larger cohort.     

Armadillo 1.1: an original workflow platform for designing and conducting phylogenetic analysis and simulations

In this paper we introduce Armadillo v1.1, a novel workflow platform dedicated to designing and conducting phylogenetic studies, including comprehensive simulations. A number of important phylogenetic and general bioinformatics tools have been included in the first software release. As Armadillo is an open-source project, it allows scientists to develop their own modules as well as to integrate existing computer applications. Using our workflow platform, different complex phylogenetic tasks can be modeled and presented in a single workflow without any prior knowledge of programming techniques. The first version of Armadillo was successfully used by professors of bioinformatics at Université du Quebec à Montreal during graduate computational biology courses taught in 2010-11. The program and its source code are freely available at: .     

Biochemical and functional characterization of high-affinity urotensin II receptors in rat cortical astrocytes

The urotensin II (UII) gene is primarily expressed in the central nervous system, but the functions of UII in the brain remain elusive. Here, we show that cultured rat astrocytes constitutively express the UII receptor (UT). Saturation and competition experiments performed with iodinated rat UII ([(125)I]rUII) revealed the presence of high- and low-affinity binding sites on astrocytes. Human UII (hUII) and the two highly active agonists hUII(4-11) and [3-iodo-Tyr9]hUII(4-11) were also very potent in displacing [(125)I]rUII from its binding sites, whereas the non-cyclic analogue [Ser5,10]hUII(4-11) and somatostatin-14 could only displace [(125)I]rUII binding at micromolar concentrations. Reciprocally, rUII failed to compete with [(125)I-Tyr0,D-Trp8]somatostatin-14 binding on astrocytes. Exposure of cultured astrocytes to rUII stimulated [(3)H]inositol incorporation and increased intracellular Ca(2+) concentration in a dose-dependent manner. The stimulatory effect of rUII on polyphosphoinositide turnover was abolished by the phospholipase C inhibitor U73122, but only reduced by 56% by pertussis toxin. The GTP analogue Gpp(NH)p caused its own biphasic displacement of [(125)I]rUII binding and provoked an affinity shift of the competition curve of rUII. Pertussis toxin shifted the competition curve towards a single lower affinity state. Taken together, these data demonstrate that rat astrocytes express high- and low-affinity UII binding sites coupled to G proteins, the high-affinity receptor exhibiting the same pharmacological and functional characteristics as UT.     

Pectic polysaccharides from Biophytum petersianum Klotzsch, and their activation of macrophages and dendritic cells

The Malian medicinal plant Biophytum petersianum Klotzsch (Oxalidaceae) is used as a treatment against various types of illnesses related to the immune system, such as joint pains, inflammations, fever, malaria, and wounds. A pectic polysaccharide obtained from a hot water extract of the aerial parts of B. petersianum has previously been reported to consist of arabinogalactans types I and II (AG-I and AG-II), probably linked to a rhamnogalacturonan backbone. We describe here further structural characteristics of the main polysaccharide fraction (BP1002) and fractions obtained by enzymatic degradations using endo-alpha-d-(1-->4)-polygalacturonase (BP1002-I to IV). The results indicate that in addition to previously reported structures, rhamnogalacturan type II and xylogalacturonan areas appear to be present in the pectic polymer isolated from the plant. Atomic force microscopy confirmed the presence of branched structures, as well as a polydisperse nature. We further tested whether the BP1002 main fraction or the enzymatically degraded products could induce immunomodulating activity through stimulation of subsets of leukocytes. We found that macrophages and dendritic cells were activated by BP1002 fractions, while there was little response of T cells, B cells, and NK cells. The enzymatic treatment of the BP1002 main fraction gave important information on the structure-activity relations. It seems that the presence of rhamnogalacturonan type I is important for the bioactivity, as the bioactivity decreases with the decreased amounts of rhamnose, galactose, and arabinose. The demonstration of bioactivity by the plant extracts might indicate the mechanisms behind the traditional medical use of the plant.     

Unexpected high circulation of <Emphasis Type="Italic">Plasmodium vivax</Emphasis> in asymptomatic children from Kédougou,southeastern Senegal

Background

Malaria in Senegal is due essentially to infections by Plasmodium falciparum and, to a lesser extent to Plasmodium malariae and Plasmodium ovale. By the use of molecular methods, detection of Plasmodium vivax has been recently reported in the region of Kedougou, raising the question of appraisal of its potential prevalence in this setting.

Methods

A retrospective serological study was carried out using 188 samples taken from 2010 to 2011 in a longitudinal school survey during which 48 asymptomatic children (9–11 years) were recruited. Four collections of samples collected during two successive dry and rainy seasons were analysed for antibody responses to P. vivax and P. falciparum. Recombinant P. falciparum and P. vivax MSP1 antigens and total P. falciparum schizont lysate from African 07/03 strain (adapted to culture) were used for ELISA. Nested PCR amplification was used for molecular detection of P. vivax.

Results

A surprising high prevalence of IgG responses against P. vivax MSP1 was evidenced with 53% of positive samples and 58% of the individuals that were found positive to this antigen. There was 77% of responders to P. falciparum outlined by 63% of positive samples. Prevalence of responders did not differ as function of seasons. Levels of antibodies to P. falciparum fluctuated with significant increasing between dry and rainy season (P < 0.05), contrary to responses to P. vivax. There was a significant reciprocal relationship (P < 10^?3) between antibody responses to the different antigens, but with weak coefficient of correlation (Rho around 0.3) underlining a variable profile at the individual level. Clear molecular signature was found in positive IgG to P. vivax msp1 samples by PCR.

Conclusion

This cross-sectional longitudinal study highlights the unexpected high circulation of P. vivax in this endemic area. Sero-immunology and molecular methods are powerful additive tools to identify endemic sites where relevant control measures have to be settled and monitored.

     

A Common Mechanism of Inhibition of the Mycobacterium tuberculosis Mycolic Acid Biosynthetic Pathway by Isoxyl and Thiacetazone

Isoxyl (ISO) and thiacetazone (TAC), two prodrugs once used in the clinical treatment of tuberculosis, have long been thought to abolish Mycobacterium tuberculosis (M. tuberculosis) growth through the inhibition of mycolic acid biosynthesis, but their respective targets in this pathway have remained elusive. Here we show that treating M. tuberculosis with ISO or TAC results in both cases in the accumulation of 3-hydroxy C₁₈, C₂₀, and C₂₂ fatty acids, suggestive of an inhibition of the dehydratase step of the fatty-acid synthase type II elongation cycle. Consistently, overexpression of the essential hadABC genes encoding the (3R)-hydroxyacyl-acyl carrier protein dehydratases resulted in more than a 16- and 80-fold increase in the resistance of M. tuberculosis to ISO and TAC, respectively. A missense mutation in the hadA gene of spontaneous ISO- and TAC-resistant mutants was sufficient to confer upon M. tuberculosis high level resistance to both drugs. Other mutations found in hypersusceptible or resistant M. tuberculosis and Mycobacterium kansasii isolates mapped to hadC. Mutations affecting the non-essential mycolic acid methyltransferases MmaA4 and MmaA2 were also found in M. tuberculosis spontaneous ISO- and TAC-resistant mutants. That MmaA4, at least, participates in the activation of the two prodrugs as proposed earlier is not supported by our biochemical evidence. Instead and in light of the known interactions of both MmaA4 and MmaA2 with HadAB and HadBC, we propose that mutations affecting these enzymes may impact the binding of ISO and TAC to the dehydratases.     

Spatial Segregation between Invasive and Native Commensal Rodents in an Urban Environment: A Case Study in Niamey,Niger

Invasive rodents have been responsible for the diffusion worldwide of many zoonotic agents, thus representing major threats for public health. Cities are important hubs for people and goods exchange and are thus expected to play a pivotal role in invasive commensal rodent dissemination. Yet, data about urban rodents'' ecology, especially invasive vs. native species interactions, are dramatically scarce. Here, we provide results of an extensive survey of urban rodents conducted in Niamey, Niger, depicting the early stages of rodent bioinvasions within a city. We explore the species-specific spatial distributions throughout the city using contrasted approaches, namely field sampling, co-occurrence analysis, occupancy modelling and indicator geostatistics. We show that (i) two species (i.e. rural-like vs. truly commensal) assemblages can be identified, and that (ii) within commensal rodents, invasive (Rattus rattus and Mus musculus) and native (Mastomys natalensis) species are spatially segregated. Moreover, several pieces of arguments tend to suggest that these exclusive distributions reflect an ongoing native-to-invasive species turn over. The underlying processes as well as the possible consequences for humans are discussed.