In vitro emergence of rifampicin resistance in Propionibacterium acnes and molecular characterization of mutations in the rpoB gene

Objectives Activity of rifampicin against Propionibacterium acnes biofilms was recently demonstrated, but rifampicin resistance has not yet been described in this organism. We investigated the in vitro emergence of rifampicin resistance in P. acnes and characterized its molecular background. Methods P. acnes ATCC 11827 was used (MIC 0.007 mg/L). The mutation rate was determined by inoculation of 109 cfu of P. acnes on rifampicin-containing agar plates incubated anaerobically for 7 days. Progressive emergence of resistance was studied by serial exposure to increasing concentrations of rifampicin in 72 h cycles using a low (106 cfu/mL) and high (108 cfu/mL) inoculum. The stability of resistance was determined after three subcultures of rifampicin-resistant isolates on rifampicin-free agar. For resistant mutants, the whole rpoB gene was amplified, sequenced and compared with a P. acnes reference sequence (NC006085). Results P. acnes growth was observed on rifampicin-containing plates with mutation rates of 2 ± 1 cfu × 10−9 (4096× MIC) and 12 ± 5 cfu × 10−9 (4× MIC). High-level rifampicin resistance emerged progressively after 4 (high inoculum) and 13 (low inoculum) cycles. In rifampicin-resistant isolates, the MIC remained >32 mg/L after three subcultures. Mutations were detected in clusters I (amino acids 418-444) and II (amino acids 471-486) of the rpoB gene after sequence alignment with a Staphylococcus aureus reference sequence (CAA45512). The five following substitutions were found: His-437 → Tyr, Ser-442 → Leu, Leu-444 → Ser, Ile-483 → Valand Ser-485 → Leu. Conclusion The rifampicin MIC increased from highly susceptible to highly resistant values. The resistance remained stable and was associated with mutations in the rpoB gene. To our knowledge, this is the first report of the emergence of rifampicin resistance in P. acne

Interaction of ascending magma with pre-existing crustal fractures in monogenetic basaltic volcanism: an experimental approach

International audienceMagma transport through dikes is a major component of the development of monogenetic volcanic fields. These volcanic fields are characterized by numerous volcanic centers, each typically resulting from a single eruption. Therefore, magma must be transported from source to surface at different places, which raises the question of the relative importance of (1) the self-propagation of magma through pristine rock and (2) the control exerted by pre-existing fractures. To address this issue, we have carried out a series of analogue experiments to constrain the interaction of a propagating dike through a medium with pre-existing fractures. The experiments involved the injection of air into an elastic gelatin solid, which was previously cut into its upper part to simulate pre-existing fractures. The volume of the dikes, their distance from the fractures, and the ambient stress field were systematically varied to assess their influence on potential dike-fracture interactions. The results show that distance and angle between dikes and fractures influence these interactions and the dike trajectory. Dike geometry and dynamics are also affected by both the presence of the fractures and the dike volume; dikes propagating in between fractures tend to decelerate. In nature, interactions are expected for dikes and fractures separated by less than about 200 m, and dikes with a volume less than about 10 2 km3 would experience a velocity decrease. These results highlight the influence of pre-existing fractures on the mechanics and dynamics of dikes. These heterogeneities must be considered when studying the transport of magmas within the crust

A modelling investigation into the impacts of the convective parameterization on the tropical circulation

Many studies have shown that the tropical circulations (Walker and Hadley circulations) will weaken in a warmer world. This is sometimes attributed to changes in the tropical mean water cycling rate (driven by convective mass flux), which does not increase as fast as boundary layer water vapour in the tropics. However, this theory is only valid for the large scale upward convective mass flux in the tropics, not necessarily to the local circulations, which are not as energetically constrained. Here, we show that there is also a potential regime in which this argument does not hold by simply changing the convective scheme in a climate model. This regime is one in which the tropical mean convective mass flux can actually increase with warming, provided the precipitation efficiency decreases significantly. Our work supports the theory that the uniform tropical mean static stability increase is the physical driver of the weakening of the tropical circulations with climate change, which is mainly driven by the tropical mean SST increase, regardless of the change in strength of convective mass flux. The local changes in tropospheric diabatic heating from heating are shown to influence the magnitude of the weakening of the Walker circulation. We find that the precipitation efficiency decreases in an increased sea surface temperature AMIP-type experiment using the CAM4 AGCM with an alternate convective scheme using a unique mass flux closure, leading to a plausible scenario where tropical mean convective mass flux may increase, while the large-scale tropical circulations still weaken. While large-scale upward motion and convective mass flux are closely correlated spatially, the nature of this relationship can change in a warmer world if the precipitation efficiency changes. A decrease in precipitation efficiency can allow for increased upward convective mass flux, but the same tropospheric heating rate response, as the increased rate of condensational heating is offset by increased evaporational cooling. A decrease in precipitation efficiency leads to a lower heating rate per unit of upward mass flux due to a compensating increase in evaporation. The large tropical mean evaporation response seen with this scheme allows for stronger tropical mean convective updrafts, especially of the shallow variety, to balance where the evaporational cooling response is maximized

Étude numérique des instabilités de flammes prémélangées en régime laminaire

Les flammes laminaires prémélangées hydrogène/air sont susceptibles de développer des instabilities dues à des effets hydrodynamiques (connues sous le nom d’instabilités de Darrieus-Landau) et dues à des effets thermodiffusifs. Le premier est dû au changement de masse volumique du fluide tandis que l’autre est dû aux proprieties thermodiffusives des espèces. L’instabilité de la flamme se traduit par l’apparition de zones de combustion localisées que l’on appelle cellules qui se caractérisent par leur comportement auto-accélérant. Cette étude a été réalisée afin d’étudier l’influence de plusieurs paramètres sur le phénomène de cellularité : la cinétique chimique, la loi de mélange, la pression et enfin la condition initiale de perturbation. Pour ce faire, un modèle numérique a été mis en place : les équations de Navier-Stokes sont résolues en régime compressible, laminaire et instationnaire via le logiciel STAR-CCM+. Le domaine de simulation utilisé est un carré 2D de 160 000 cellules, le schema de discrétisation temporelle utilisé est un schéma implicite de second ordre alors que le schema de discrétisation spatiale est un schéma explicite de second ordre. Dans un premier temps, quatre cinétiques chimiques furent testées. Malgré un comportement global du front de flamme similaire pour chaque cinétique, des différences au niveau du nombre de cellules et de leur taille demeurent, probablement dues aux mécanismes de réaction associés à chaque cinétique. L’impact de la loi de mélange sur la cellularité fut étudié au travers de deux lois de mélange : une loi de mélange basée sur la fraction massique et la loi de mélange Mathur-Saxena, basée sur la fraction molaire. Une forte influence de ce paramètre fut observée, du fait que la conductivité thermique du mélange était modifiée et donc le nombre de Lewis également. L’impact de l’augmentation de pression se traduisit par une croissance du nombre total de cellules avec l’augmentation de pression, ainsi qu’un front de flamme de plus en plus chaotique et dentelé. Les paramètres de la perturbation initiale furent étudiés dans un dernier temps (amplitudes de perturbation et fréquence d’oscillation) et indiquèrent un fort impact de ces paramètres sur la cellularité, avec notamment une modification importante du front de flamme et de la taille des cellules. Cette étude a permis d’étudier l’influence de plusieurs paramètres sur le phénomène de cellularité, en utilisant un modèle simple d’ordre 2

Diversity in Acinetobacter baumannii isolates from paediatric cancer patients in Egypt

Acinetobacter baumannii is an important nosocomial pathogen, commonly causing infections in immunocompromised patients. It is increasingly reported as a multidrug-resistant organism, which is alarming because of its capability to resist all available classes of antibiotics including carbapenems. The aim of this study was to examine the genetic and epidemiological diversity of A. baumannii isolates from paediatric cancer patients in Egypt, by sequencing the intrinsic blaOXA -51-like gene, genotyping by pulsed-field gel electrophoresis and multi-locus sequence typing in addition to identifying the carbapenem-resistance mechanism. Results showed a large diversity within the isolates, with eight different blaOXA -51-like genes, seven novel sequence types and only 28% similarity by pulsed-field gel electrophoresis. All three acquired class-D carbapenemases (OXA-23, OXA-40 and OXA-58) were also identified among these strains correlating with resistance to carbapenems. In addition, we report the first identification of ISAba2 upstream of blaOXA -51-like contributing to high-level carbapenem resistance. This indicates the presence of several clones of A. baumannii in the hospitals and illustrates the large genetic and epidemiological diversity found in Egyptian strains

Interaction of Cutibacterium (formerly Propionibacterium) acnes with bone cells: a step toward understanding bone and joint infection development

Cutibacterium acnes (formerly Propionibacterium acnes) is recognized as a pathogen in foreign-body infections (arthroplasty or spinal instrumentation). To date, the direct impact of C. acnes on bone cells has never been explored. The clade of 11 C. acnes clinical isolates was determined by MLST. Human osteoblasts and osteoclasts were infected by live C. acnes. The whole genome sequence of six isolates of this collection was analyzed. CC36 C. acnes strains were significantly less internalized by osteoblasts and osteoclasts than CC18 and CC28 C. acnes strains (p ≤ 0.05). The CC18 C. acnes ATCC6919 isolate could survive intracellularly for at least 96 hours. C. acnes significantly decreased the resorption ability of osteoclasts with a major impact by the CC36 strain (p ≤ 0.05). Genome analysis revealed 27 genes possibly linked to these phenotypic behaviors. We showed a direct impact of C. acnes on bone cells, providing new explanations about the development of C. acnes foreign-body infections

Cutibacterium acnes (Propionibacterium acnes) and acne vulgaris: a brief look at the latest updates

While the commensal bacterium Propionibacterium acnes (P. acnes) is involved in the maintenance of a healthy skin, it can also act as an opportunistic pathogen in acne vulgaris. The latest findings on P. acnes shed light on the critical role of a tight equilibrium between members of its phylotypes and within the skin microbiota in the development of this skin disease. Indeed, contrary to what was previously thought, proliferation of P. acnes is not the trigger of acne as patients with acne do not harbour more P. acnes in follicles than normal individuals. Instead, the loss of the skin microbial diversity together with the activation of the innate immunity might lead to this chronic inflammatory condition. This review provides results of the most recent biochemical and genomic investigations that led to the new taxonomic classification of P. acnes renamed Cutibacterium acnes (C. acnes), and to the better characterisation of its phylogenetic cluster groups. Moreover, the latest data on the role of C. acnes and its different phylotypes in acne are presented, providing an overview of the factors that could participate in the virulence and in the antimicrobial resistance of acne-associated strains. Overall, this emerging key information offers new perspectives in the treatment of acne, with future innovative strategies focusing on C. acnes biofilms and/or on its acne-associated phylotypes