Cell surface properties of two differently virulent strains of Acinetobacter baumannii isolated from a patient

The aim of this study was to unravel, by focusing on cell surface properties, the underlying virulence factors contributing to the difference in the pathogenicity observed in two Acinetobacter baumannii strains isolated from the same patient. The two strains were phenotypically different: (i) a mucoid strain (AB-M), highly virulent in a mouse model of pneumonia, and (ii) a nonmucoid strain (AB-NM), moderately virulent in the same model. The study of the cell surface properties included the microbial adhesion to solvents method, the measurement of the electrophoretic mobility of bacteria, the analysis of biofilm formation by calcofluor white staining, the adherence to silicone catheters, and scanning electron microscopy. The AB-NM strain was more hydrophobic, more adherent to silicone catheters, and produced more biofilm than the AB-M strain. Scanning electron microscopy showed bacterial cells with a rough surface and the formation of large cell clusters for AB-NM whereas the AB-M strain had a smooth surfa..., Le but de cette etude était d’étudier, en se focalisant sur les propriétés de surface des bactéries, des caractères potentiellement impliqués dans la différence de pouvoir pathogène de deux souches d’Acinetobacter baumannii isolées chez un même patient. Ces souches étaient phénotypiquement différentes : une souche mucoïde (AB-M) caractérisée par un pouvoir pathogène élevé dans un modèle expérimental murin de pneumopathie, et une souche non mucoïde (AB-NM), plus faiblement pathogène dans le même modèle. L’étude des propriétés de surface a utilisé la méthode d’adhésion des bactéries aux solvants, la mesure de la mobilité électrophorétique des bactéries, l’analyse de la formation de biofilm par marquage au calcofluor, l’adhésion à des cathéters en silicone, et la microscopie électronique à balayage. La souche AB-NM est apparue plus hydrophobe, plus adhérente aux cathéters, et plus productrice de biofilm que la souche AB-M. L’observation en microscopie électronique à balayage a montré des bactéries à surface ..

The Arabidopsis thaliana-Alternaria brassicicola pathosystem: A model interaction for investigating seed transmission of necrotrophic fungi

Seed transmission constitutes a major component of the parasitic cycle for several fungal pathogens. However, very little is known concerning fungal or plant genetic factors that impact seed transmission and mechanisms underlying this key biological trait have yet to be clarified. Such lack of available data could be probably explained by the absence of suitable model pathosystem to study plant-fungus interactions during the plant reproductive phase

Viability of osteocytes in bone autografts harvested for dental implantology

Bone autograft remains a very useful and popular way for filling bone defects. In maxillofacial surgery or implantology, it is used to increase the volume of the maxilla or mandible before placing dental implants. Because there is a noticeable delay between harvesting the graft and its insertion in the receiver site, we evaluated the morphologic changes at the light and transmission electron microscopy levels. Five patients having an autograft (bone harvested from the chin) were enrolled in the study. A small fragment of the graft was immediately fixed after harvesting and a second one was similarly processed at the end of the grafting period when bone has been stored at room temperature for a 20 min ± 33 s period in saline. A net increase in the number of osteocyte lacunae filled with cellular debris was observed (+41.5%). However no cytologic alteration could be observed in the remaining osteocytes. The viability of these cells is known to contribute to the success of autograft in association with other less well-identified factors

Impact of the unfolded protein response on the pathogenicity of the necrotrophic fungus Alternaria brassicicola

The unfolded protein response (UPR) is an important stress signalling pathway involved in the cellular development and environmental adaptation of fungi. We investigated the importance of the UPR pathway in the pathogenicity of the plant necrotrophic fungus Alternaria brassicicola, which causes black spot disease on a wide range of Brassicaceae. We identified the AbHacA gene encoding the major UPR transcription regulator in A. brassicicola. Deletion of AbHacA prevented induction of the UPR in response to endoplasmic reticulum stress. Loss of UPR in mutants resulted in a complete loss of virulence and was also associated with a cell wall defect and a reduced capacity for secretion. In addition, our results showed that the UPR was triggered by treatment of mycelia with camalexin, i.e. the major Arabidopsis thaliana phytoalexin, and that strains lacking functional AbHacA exhibited increased in vitro susceptibility to antimicrobial plant metabolites. We hypothesize that the UPR plays a major role in fungal virulence by altering cell protection against host metabolites and by reducing the ability of the fungus to assimilate nutrients required for growth in the host environment. This study suggests that targeting the UPR pathway would be an effective plant disease control strategy

Behaviour studies of new strains of Venturia pirina isolated from "conference" cultivar on a range of pear cultivars

2 Vol.Behaviour studies of new strains of [i]Venturia pirina[/i] isolated from "conference" cultivar on a range of pear cultivars. Xth International Symposium on Pear Growin