Molecular characterisation of Staphylococcus aureus strains isolated from small and large ruminants reveals a host rather than tissue specificity.

International audienceStaphylococcus aureus is an important pathogen in domestic ruminants. The main objective of this study was to determine the similarity of epidemiologically unrelated S. aureus isolates from bovine, ovine, and caprine hosts regardless the locus of isolation (nares and udder). By pulsed-field gel electrophoresis, seven major pulsotypes were identified among 153 isolates recovered from 12 different regions of France as well as from Brazil, the USA and Belgium. Typing of the accessory gene regulator (agr) and capsular (cap) serotype was carried out on all the isolates and revealed the predominance of agr I and III and of cap8 regardless the ruminant host species. Screening for methicilin-resistant S. aureus (MRSA) was carried out by disk diffusion and revealed a prevalence of only 3.2% of MRSA among the strains tested. These results suggest the existence of a host rather than tissue specificity among S. aureus isolates colonising the ruminant species and suggest a limited transmission of those isolates between large (bovine) and small (ovine-caprine) ruminants. The agr class and cap types correlated with pulsotype clusters rather than with a specific host species. Antimicrobial resistance appears not to have contributed to the predominance of any given genotypes, and MRSA prevalence appears very low in ruminant isolates

Development of serological proteome analysis of mastitis by Staphylococcus aureus in ewes.

International audienceStaphylococcus aureus is a major agent of mastitis in ruminants worldwide. So far, efficient measures for its prophylaxis (including vaccination) have proven to be unsuccessful and there is a need for a better understanding of the host response to udder infection by S. aureus. Serological proteome analysis (SERPA) is a promising technique that can be used to identify S. aureus immuno-dominant determinants providing that bacterial culture conditions used to grow S. aureus strains for protein sample preparation mimic the context of mastitis. A S. aureus strain was used in experimental mastitis to generate sheep serum used to determine the best growth conditions for SERPA. Sera collected in the field from different ewes suffering from mastitis by S. aureus were used to confirm experimental observations. Three different culture media (BHI, whey and iron-depleted RPMI) were tested. The influence of aeration and growth phase on protein production was also evaluated by immuno-detection of protein samples prepared from cultures grown in different conditions and obtained from different culture fractions (supernatant, cell wall, and total lysates). Our results showed that culturing in iron-depleted RPMI with (secreted proteins, prepared from stationary phase) or without aeration (cell wall proteins, prepared from early stationary phase, and total proteins, prepared from exponential phase) is the condition that best mimics growth in vivo during mastitis and this in vitro growth condition is to be used henceforth in experiments involving SERPA

Deformation of the N=Z nucleus 76Sr using beta-decay studies

A novel method of deducing the deformation of the N=Z nucleus 76Sr is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of QRPA calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large Total Absorption gamma Spectrometer, "Lucrecia", newly installed at CERN-ISOLDE.Comment: Accepted in Phys. Rev. Letter

Adaptive optics in high-contrast imaging

The development of adaptive optics (AO) played a major role in modern astronomy over the last three decades. By compensating for the atmospheric turbulence, these systems enable to reach the diffraction limit on large telescopes. In this review, we will focus on high contrast applications of adaptive optics, namely, imaging the close vicinity of bright stellar objects and revealing regions otherwise hidden within the turbulent halo of the atmosphere to look for objects with a contrast ratio lower than 10^-4 with respect to the central star. Such high-contrast AO-corrected observations have led to fundamental results in our current understanding of planetary formation and evolution as well as stellar evolution. AO systems equipped three generations of instruments, from the first pioneering experiments in the nineties, to the first wave of instruments on 8m-class telescopes in the years 2000, and finally to the extreme AO systems that have recently started operations. Along with high-contrast techniques, AO enables to reveal the circumstellar environment: massive protoplanetary disks featuring spiral arms, gaps or other asymmetries hinting at on-going planet formation, young giant planets shining in thermal emission, or tenuous debris disks and micron-sized dust leftover from collisions in massive asteroid-belt analogs. After introducing the science case and technical requirements, we will review the architecture of standard and extreme AO systems, before presenting a few selected science highlights obtained with recent AO instruments.Comment: 24 pages, 14 figure