Entéropathie du nouveau-né prématuré : approche clinique, métagénomique et métabolomique

L'Entérocolite Ulcéro-Nécrosante (ECUN) est la pathologie intestinale la plus grave chez les nouveau-nés prématurés. Aucun essai clinique ou étude de cohorte ne s'est intéressé uniquement au stade I de l'ECUN. Nous avons analysé des échantillons de selles prélevées chez des nourrissons de moins de 34 semaines d'âge gestationnel, dont 11 nourrissons qui ont développé une entéropathie (ECUN-I)) et 21 témoins appariés. Les communautés bactériennes des selles ont été profilées par séquençage du gène 16S de l'ARNr bactérien. Le métabolome fécal a été analysé par NMR. Au cours de la première décade de vie (J1 à 10), les échantillons de nourrissons entéropathes tendaient vers une diversité alpha plus faible que chez les témoins avec une différence significative dans la répartition des communautés bactériennes, mais pas au niveau des métabolites fécaux. Dans la deuxième décade (J11-J20), l'analyse du microbiome ne montre pas de différence entre entéropathes et témoins mais l'analyse métabolomique montre une diminution significative du taux de sérine dans le groupe des entéropathes. Entre J21 et J30, Bacillus, Staphylocococcus, Bacteroidetes et Streptococcus sont les groupes bactériens les plus abondants chez les entéropathes, alors que les genres Klebsiella et Raoultella sont plus abondants chez les témoins. Au-delà de 30 jours de vie, les témoins ont un microbiote plus riche en entérobactéries (Klebsiella et Enterobacter) que les entéropathes. Les divergences au niveau métabolomique sont plus importantes au cours du deuxième mois de vie. Les modifications structurelles et fonctionnelles du microbiote intestinal semblent plus reconnaissables à la troisième décade de la vie, comparativement aux enfants témoins. La fonctionnalité du microbiote intestinal est plus affectée par les facteurs maternels et infantiles alors que la structure du microbiote intestinal semble plus stable. Ces données pourraient fournir de nouvelles cibles microbiennes pour lutter contre la progression de l'ECUN dès le stade 1.Necrotizing enterocolitis (NEC) is the most serious intestinal pathology in preterm infants. No clinical trial or cohort studies included only stage I of NEC (NEC-1). We analysed stool samples collected from infants under 34 weeks of gestational age, including 11 infants who developed enteropathy (NEC-1 group) and 21 matched controls. Fecal Bacterial communities were profiled by sequencing the 16S rRNA bacterial gene. Faecal metabolomic profiles were analysed by NMR. During the first ten days of life (d1-10), samples from NEC-1 infants showed a lower alpha diversity than controls with a significant difference in the distribution of bacterial communities but not in faecal metabolome. Between d11-d20, microbiome did not differ between NEC-1 infants and controls, but metabolomic analysis showed a significant decrease in serine levels in NEC-1 infants. Between d21 and d30, Bacillus, Staphylocococcus, Bacteroidetes and Streptococcus bacterial groups were more abundant in NEC-1 infants than in controls, whereas Klebsiella and Raoultella species were more abundant in controls. Beyond 30 days of life, controls showed a microbiota richer in Klebsiella and Enterobacter than NEC-1 infants. Leucine levels in faeces were lower in NEC-1 infants. The modifications of gut microbiota and microbiome during NEC-1 development appear more distinguishable by the third decade of life, when compared to healthy children. These data may suggest new microbial targets to fight/blunt the progression of NEC as early as by stage 1

Study of a self quenching streamer mode in pure gases of DME and isobutane

A self quenching streamer (SQS), or limited streamer mode has been studied in single wire chambers with cross-sections 12x12 mm and wire diameters 15, 25 and 50 microns. Chambers were filled with either pure dimethyl ether (DME) or isobutane gases and irradiated with Gd-148 alpha and Fe-55 x-ray sources. Clear transitions from a proportional to 100% SQS mode were observed on all three diameter wires with both gases irradiated with alpha particles. Double SQS discharges due to inclined tracks observed in DME gas allowed an estimation of a streamer size along the wire of less than 1 mm. The second SQS discharge appears less than 1 mm from the first within about 500 ns. Charge spectra obtained with DME irradiated with Fe-55 x-rays might also be interpreted as a transition to a SQS mode, although no direct evidence of that was seen in the observed pulse shapes

EROS Variable Stars : Discovery of Beat Cepheids in the Small Magellanic Cloud and the effect of metallicity on pulsation

We report the discovery of eleven beat Cepheids in the Small Magellanic Cloud, using data obtained by the EROS microlensing survey. Four stars are beating in the fundamental and first overtone mode (F/1OT), seven are beating in the first and second overtone (1OT/2OT). The SMC F/1OT ratio is systematically higher than the LMC F/1OT, while the 1OT/2OT period ratio in the SMC Cepheids is the same as the LMC one.Comment: 4 pages, Latex file with 4 .ps figures. accepted for publication in A A Letter

The effect of metallicity on the Cepheid distance scale and its implications for the Hubble constant (H0H_0) determination

Recent HST determinations of the expansion's rate of the Universe (the Hubble constant, H_0) assumed that the Cepheid Period-Luminosity relation at V and I are independent of metallicity (Freedman, et al., 1996, Saha et al., 1996, Tanvir et al., 1995). The three groups obtain different vales for H_0. We note that most of this discrepancy stems from the asumption (by both groups) that the Period-Luminosity relation is independent of metallicity. We come to this conclusion as a result of our study of the Period-Luminosity relation of 481 Cepheids with 3 millions two colour measurements in the Large Magellanic Cloud and the Small Magellanic Cloud obtained as a by-product of the EROS microlensing survey. We find that the derived interstellar absorption corrections are particularly sensitive to the metallicity and when our result is applied to recent estimates based on HST Cepheids observations it makes the low-H_0 values higher and the high-H_0 value lower, bringing those discrepant estimates into agrement around $H_0 \approx 70 km/s Mpc^{-1}$.Comment: 4 pages, Latex, with 2 .ps accepted for publication astronomy and astrophysics Letter

Observational Limits on Machos in the Galactic Halo

We present final results from the first phase of the EROS search for gravitational microlensing of stars in the Magellanic Clouds by unseen deflectors (machos: MAssive Compact Halo Objects). The search is sensitive to events with time scales between 15 minutes and 200 days corresponding to deflector masses in the range 1.e-7 to a few solar masses. Two events were observed that are compatible with microlensing by objects of mass of about 0.1 Mo. By comparing the results with the expected number of events for various models of the Galaxy, we conclude that machos in the mass range [1.e-7, 0.02] Mo make up less than 20% (95% C.L.) of the Halo dark matter.Comment: 4 pages, 3 Postscript figures, to be published in Astronomy & Astrophysic

EROS VARIABLE STARS : FUNDAMENTAL-MODE AND FIRST OVERTONE CEPHEIDS IN THE BAR OF THE LARGE MAGELLANIC CLOUD

We present CCD phase-binned light curves at 490 nm for 97 Cepheid variable stars in the bar of the LMC. The photometry was obtained as part of the French EROS project and has excellent phase coverage, permitting accurate decomposition into Fourier components. We identify as `sinusoidal' or s-Cepheids those stars with periods less than 5.5 d and small second-harmonic components. These stars comprise $\sim$30% of our sample and most form a sequence $\sim$1 mag brighter than the LMC classical Cepheids in the period-luminosity diagram. They are also generally bluer and have lower-amplitude light curves. We infer that the s-Cepheids are first-overtone pulsators because, when their periods are converted to expected fundamental-mode values, they obey a common period-luminosity-colour relation with classical Cepheids. This also confirms the reality of the colour term in the Cepheid period-luminosity-colour relation. Further, the blue edge of the classical Cepheid instability strip agrees well with the theoretical calculations for the fundamental mode made by Chiosi et al. (1993) for the Hertzsprung-Russell and period-luminosity diagrams, but we find that our observed s-Cepheids are $>0.2$ mag brighter and bluer than the Chiosi et al.\ predictions for the first-overtone. We identify a number of features in plots of our stars' Fourier-component amplitude ratios and phase differences. These features have been identified with resonances between different pulsation modes. In the LMC we find these features seem to occur at periods very similar to Galactic ones for classical Cepheids, but at different periods for s-Cepheids. We discover a double-mode Cepheid in the LMC, for which $P({\rm first overtone})/P({\rm fundamental}) = 0.710 \pm 0.001$, very similar to observed ratios for Galactic double-mode Cepheids.Comment: 19 pages, uuencoded compressed PS file, including 14 figures. Accepted for publication in Astronomy and Astrophysics, February-2-199

Metallicity Effects on the Cepheid Extragalactic Distance Scale from EROS photometry in LMC and SMC

This is an investigation of the period-luminosity relation of classical Cepheids in samples of different metallicity. It is based on 481 Cepheids in the Large and Small Magellanic Clouds from the blue and red filter CCD observations (most similar to V_J & R_J) of the French EROS microlensing project. The data-set is complete and provides an excellent basis for a differential analysis between LMC and SMC. In comparison to previous studies of effects on the PL-relation, the EROS data-set offers extremely well-sampled light curves and well-filled instability strips. This allows reliable separation of Cepheids pulsating in the fundamental and the first overtone mode and derivation of differential reddening. Our main result concerns the determination of distances to galaxies which are inferred by using the LMC as a base and using two color photometry to establish the amount of reddening. We find a zero-point offset between SMC and LMC which amounts to a difference between inferred and true distance modulus of 0.14 \pm 0.06 mag in the VI_c system. The offset is exactly the same in both sets of PL-relations - of the fundamental and of the first overtone mode Cepheids. No effect is seen on the slopes of the PL-relations, although the fundamental and the first overtone mode Cepheids have different PL slopes. We attribute the color and the zero-point offset to the difference in metallicity between the SMC and LMC Cepheids. A metallicity effect of that small magnitude still has important consequencies for the inferred Cepheid distances and the determination of H_0. When applied to recent estimates based on HST Cepheid observations, our metallicity dependence makes the low-H_0 values (Sandage et al. 1994) higher and the high-H_0 values (Freedman et al. 1994b) lower, thus bringing thoseComment: 14 pages, Latex, with 8 .ps accepted for publication in astronomy and astrophysic

AGAPEROS: Searches for microlensing in the LMC with the Pixel Method; 2, Selection of possible microlensing events

We apply the pixel method of analysis (sometimes called ``pixel lensing'') to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Mo Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method should detect 10 to 20 times more microlensing events for M>0.05 Mo Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1 -- 0.5 Mo, a pixel analysis of the three-year EROS-1 data set covering 0.39 deg^2 would yield 4 events.We apply the pixel method of analysis (sometimes called ''pixel lensing'') to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Mo Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method, applied to crowded fields, should detect 10 to 20 times more microlensing events for M>0.05 Mo Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1-0.5 M $\bigodot$, a pixel analysis of the three-year EROS-1 data set covering $0.39deg^{2}$ would yield $\simeq 4$ events